Southwest B737 Overrun @ Chcago MDW [Archive] - Page 2

TheShadow

18th Dec 2005, 23:51

From Belgique's post: d. Have the autobrake cut-in dependent upon G/A sensing circuit #1 plus G/A sensing circuit #2 (which is nosewheel oleo depression micro-switch actuation by NLG ON). That stops brakes cutting in while NLG is still airborne and causing a heavy nose hit de-rotation. And there is a difference between maximum wheel-braking and maximum effective aircraft braking. For the former, standing on the toe-pedals will just produce wheel-lock and tire-skid on a contaminated runway (i.e. ineffectual for stopping). In the latter case, minimizing the brakes release time of the anti-skid by maximizing the weight on the wheels will stop you in the shortest distance. Despite the NTSB finding on the 182kt Burbank touchdown, that max wt on wheels will be achieved by an autobrake married to some hefty back-stick introduced after the nose-gear is on. MLG braking produces a strong nose-down pitching moment and the backstick counters that. The important and oft-overlooked nett effect is that the MLG gets pushed into the deck...... for the very best auto-braking on slick runways.

e._Increase spoiler panel size and deployment rate => increased effectiveness for lift-dumping, => earlier weight-on-wheels for avoiding aquaplaning and maximizing tire rotational torques (which minimizes auto-brake cycling). The less frequent the brake-valves have to modulate to permit continued wheel-spin, the more effective is the auto-braking. This would also make for safer take-off aborts. To blow the tire you must first stop the wheel (is the practical aspect). That's least likely to happen if you maximize weight-on-wheels courtesy of the spoilers. What else can you do to maximize weight-on-wheels? Per d. above, use back-stick once you are on to stay and braking is heavy. Up elevator forces the main-gears down into the ground. Conversely, forward stick (down elevator) would induce wheel-barrowing. Stopping effectively is a real science.

The bits in blue (increasing effective weight on wheels via backstick under braking) is something I'd not thought about or been taught. T'would seem quite logical and valid as far as techniques go.

Thoughts?

Airbubba

19th Dec 2005, 00:42

>>Thoughts?

Kinda like aerodynamic braking, might work in lightplanes, don't believe I'd try it on a modern widebody where tailstrikes are soooo easy...

barit1

19th Dec 2005, 00:53

Kinda like aerodynamic braking,

In a sense I suppose...

Except instead of going for mainplane lift (Cl + Cd), you are using tailplane lift (negative) to increase the MLG load. As long as the nosegear remains on the deck you don't put the wing to work, and you get whatever nosegear steering is available.

Airbubba

19th Dec 2005, 01:19

What I meant was it is a technique that may work on smaller aircraft but does not always scale up well to larger ones. The longer widebodies are notorious for wanting to do a tailstand on rollout if you're not careful, particularly with the fuel efficient aft cg that many operators strive to achieve in their loading.

At least that's how it works on my MS Flight Simulator <g>...

UNCTUOUS

19th Dec 2005, 02:24

Works for me as advertised.

There's no CofG effect as the nose-down pitching moment due to an effective weight-shift forward (due braking) keeps the nose-gear pinned. It's taught in the military - at least it was when I went through advanced flight school.

It effectively increases the MLG footprint and weight on wheels - and so stops the anti-skid from cycling excessively. The end result is much more effective braking - particularly on slippery runways in the wet.

I recall seeing a study on aquaplaning where it was a recommended braking technique.

Airbubba suggests that it's an effect that cannot be scaled up to heavy metal. Don't think so.........

And it's got nought to do with aerodynamic braking because that's all about holding the nose-gear off...... and generating some aerody drag.

Dream Land

19th Dec 2005, 05:30

amos2

19th Dec 2005, 09:01

barit1 & UNCTUOUS have a neat little discussion going on here about,err, I'm not sure what!

Strange don't you think that neither Boeing or Airbus say anything in their manuals about this "new revelation" of aerodynamic theory that they're going on about!

As a matter of fact, I can't remember Douglas, Convair, Fokker, or anyone else for that matter, being aware of this amazing radical landing technique for heavy jets!

Still, we're never too old to learn are we? :ok:

tribo

19th Dec 2005, 11:18

I guess the "Stopping on Slippery Runways" info from Boeing on this link should be of interest:

http://rds.yahoo.com/_ylt=AnYEH_.rO9p9u4MSrsLJohhXNyoA;_ylu=X3oDMTE2Mzl0bXAxBGNvb G8DdwRsA1dTMQRwb3MDMQRzZWMDc3IEdnRpZANERlg1XzMw/SIG=12otd6no0/EXP=1135080805/**http%3a//www.pilots.or.kr/upfile/aip/9AAAA_StoppingonSlipperyRwys2.ppt

TheShadow

19th Dec 2005, 11:18

amos2

Maybe go back a page and look at the post upon which their discussion is based (by Belgique - as part-quoted in highlit blue and commented upon by "TheShadow" and later by UNCTUOUS). It's pretty fundamental stuff - but so often overlooked. Perhaps that's because it's just not in some syllabi.

Despite your perhaps not being able to comprehend the concept, it's in no ways revolutionary - so maybe try going back to first principles. Then if you have a valid reason why it's aerodynamically unsound, well let fly with some specifics matey. There's no point ranting about obscure abstractions.

It's interesting to pose the question: "I wonder how many airplanes have gone off the end over the years just because their pilots have no idea how to brake most effectively?". My answer would have to be: "A helluva lot, particularly in the more ignorant areas of the world."

I doubt that Boeing, Airbus, Embraer, Fokker or any of the other makers would take contest with what is, after all, just a fundamental, but very easily overlooked, flight-control technique.

tribo

19th Dec 2005, 12:00

The Airbus perspective on contaminated runways operations can be found at this link:

http://www.wingfiles.com/files/safety/gettingtogripswithcoldweatheroperations.pdf

UNCTUOUS

19th Dec 2005, 12:04

Good Reference tribo - even though it fails to mention the advantages of post nosewheel-on backstick. The need to increase weight on wheels is evident throughout however.

Effectiveness of wheel-brakes: (page 25)
"Lift reduction due to spoiler deployment contributes greatly to the generation of effective stopping force due to wheel brakes" - pity they didn't add "as does rearward control column pressure (used to increase the effective weight upon the main-gear wheels")

Effectiveness of wheel-brakes: (page 27)
"Slippery runway - thrust reverser and aerodynamic drag become dominant stopping force as runway slipperiness increases". Graph shows clearly how brake effectiveness drops off as the degree of incipient aquaplaning increases. Backstick is the only method of countering this - it forces the MLG wheels into the runway, breaking through the viscous film.

Effectiveness of Auto-brakes: (page 28)
"Autobrake performance capability is limited by the runway friction capability"

Flare and Touchdown (page 35)
Flare should lead to a firm touchdown
Extended flare will extend touchdown and delay braking
Lower the nose as soon as main gear touches down
(Increases load on the gear)
Raise spoilers as soon as possible after touchdown (confirm auto spoiler deployment)
(Increases load on the gear)
Initiate braking once spoilers have been raised and nose wheels have contacted the runway
Apply brakes smoothly and symmetrically
suggested addition:
Once braking is under way, progressive back-pressure on the control column will increase the effective weight-on-wheels, minimize anti-skid cycling and thus maximize wheel-braking effectiveness.

Target the rollout to stop well short of the end of the runway
Initiate reverse thrust as soon as possible after touchdown
Leave margin for unexpectedly low friction due to wet rubber deposits or hydroplaning

alf5071h

19th Dec 2005, 21:03

Belgique thanks for the technical details. More issues; is the Rad Alt susceptible to errors when over strong reflective surfaces such as water / ice?

Further thoughts, what if one or both the Rad Alts is above 10ft due to error / failure? Is the reverser / spoiler logic then solely dependent on leg compression, or vice versa?

Can the reverser ‘baulk’ be trapped in the engaged state if the thrust levers are forced rearwards?

tribo thanks for the Boeing link, most enlightening. This restates the problems / unreliability of Mu measuremnt:

“If runway is reported to have slush/standing water covering, the flight crew should be suspicious of braking action reports and measured friction.”

“Ground friction measuring vehicles are unreliable when the runway is covered with a depth of contaminant that exceeds: Water - 1 mm. Slush/wet snow - 3 mm. Snow - 2.5 cm”

The presentation runs into the problems of reported braking action: numerical values of Mu are associated with the definitions “good, fair, medium, poor, nil” when calculating the landing distance, but Boeing refers pilots to PIREP’s (pilot reports). I cannot see any way of a pilot being able to give a quantifiably accurate report of braking action that relates to a performance figure, especially where different types of aircraft are involved. The presentation shows the wide variation in unfactored stopping distance due to technique or systems used on just one type.

Do the issues above mean that the industry operates on contaminated runways with a high probability that the reported braking conditions do not reflect the actual conditions? It appears that the best information would come from a report of what is on the runway - snow, wet, slush, standing water, etc and the crew then evaluate the situation (as recommended by Boeing). However, this gives opportunity for erroneous judgment, with potential for further error in the presentation of landing distance (factored / unfactored); thus, the risk of landing on a contaminated runway is much higher than we appear to realize.

It is interesting to note that manual braking gives the best unfactored stopping distance, but Boeing recommend the use of A/B Max on a slippery runway (another definition of surface condition?).

The 1000 ft air distance (737) appears somewhat short in comparison to JAA assumptions:- a 7 sec flare time with a 7% speed loss. Even if the average speed was 100 kts then the resultant 1125 ft exceeds the Boeing allowance.

--------------------
Unless specifically authorized everything else is forbidden.

Mad (Flt) Scientist

20th Dec 2005, 04:09

Maybe go back a page and look at the post upon which their discussion is based (by Belgique - as part-quoted in highlit blue and commented upon by "TheShadow" and later by UNCTUOUS). It's pretty fundamental stuff - but so often overlooked. Perhaps that's because it's just not in some syllabi.

Despite your perhaps not being able to comprehend the concept, it's in no ways revolutionary - so maybe try going back to first principles. Then if you have a valid reason why it's aerodynamically unsound, well let fly with some specifics matey. There's no point ranting about obscure abstractions.

It's interesting to pose the question: "I wonder how many airplanes have gone off the end over the years just because their pilots have no idea how to brake most effectively?". My answer would have to be: "A helluva lot, particularly in the more ignorant areas of the world."

I doubt that Boeing, Airbus, Embraer, Fokker or any of the other makers would take contest with what is, after all, just a fundamental, but very easily overlooked, flight-control technique.

You'd be surprised. The first thing the OEM will tell you is "please don't use your revenue service as an opportunity to flight test a technique that we haven't used and validated ourselves"

If there were no pitfalls to applying back stick during the landing, it WOULD be in the recommended procedures, because if one OEM found it saved even 5% off distances you can be damn sure THEY'D take credit for it if they could, and that everyone else would have no choice but to follow suit for competitive reasons.

Some of the pitfalls:

You're applying a nose-up moment, not just a download. That's going to raise the nose (or prevent it sinking so far, if you prefer). That means that you're going to generate less downforce from the wings, because they will be at a slightly higher AoA. Since the wings are far more powerful than the tail in generating lift, you may find that you are actually REDUCING the MLG download, if the wing lift increase beats out the tail downforce change.

Also, if your braking effectiveness is weak to start with, you may not have a very high decel. Which means there isn't much 'throwing the weight forward' effect to start with. In which case you ARE risking unloading the nosegear, which may cause nosewheel steering issues (either loss of effectiveness or total unload). If you start to lift the nose you also risk tailstrikes (as noted) and changes to handling characteristics. (Loss of fin effectivess, perhaps).

Can I PROVE from first principles that it's a bad idea? No. But there are negatives as well as positives, and an airliner with pax isn't the place to see which one outweighs the other.

Incidentally, aerodynamic braking on military aircraft is approved on a type-specific basis as a procedure on the basis of test and validation - and not all types can, or should, use it, for various reasons.

amos2

20th Dec 2005, 04:25

It's all in the manual, fellas...

just read the manual!

That's all you gotta do!

Simple, isn't it?

OVERTALK

20th Dec 2005, 06:49

You're applying a nose-up moment, not just a download. That's going to raise the nose (or prevent it sinking so far, if you prefer).
Also, if your braking effectiveness is weak to start with, you may not have a very high decel. Which means there isn't much 'throwing the weight forward' effect to start with. In which case you ARE risking unloading the nosegear

Not sure that I'd agree with those comments at all. The cumulative nose-down pitching moment is much stronger (and increasing as speed decreases and braking effectiveness increases). The nose-up moment able to be induced by any back-stick input is at a maximum at nosewheel touchdown and rapidly reducing thereafter (due spoiler deployment and elevator loss of effectiveness as speed reduces and braking effectiveness increases).

It's not a new technique, it's just a logical way of handling the flight controls that will achieve the best retardation in slippery conditions. Wouldn't it be nice if somebody did go to the trouble of "validating" it - and it did prove to be the answer to the (usually) only irritrating "off the far end" excursions.

Don't know where aerodynamic braking comes into it. The technique has nothing to do with holding the nosewheel off before touchdown at all. It's more about planting the nosewheel and getting the autobrake and anti-skid to work most effectively by doing what BOTH Airbus and Boeing advocate i.e. loading up the mainwheels as much as possible. The advocated technique does just that - and most effectively.

Sometimes you only need a little EQUALIZER to stop you from going off the end/ or to make up for any slight errors of judgment. The suggested technique is that and more.

tribo

20th Dec 2005, 07:54

alf5071h

From the Norwegian AIP:

A numerical expression regarding the quality of the friction levels reported in the SNOWTAM can not be provided. Tests show that the accuracy indicated in the table can not be provided using todays friction measuring devices. While the table use numbers with two digits, the tests show that only numbers with one digit can be of operational value. Utmost caution should therefore be taken when using the reported friction levels, and the use of the table must be based upon the aircraft operators own experience.

In this context:

Friction measuring devices and acceptable conditions

2.6.1 The following friction measuring devices are accepted for use at Norwegian aerodromes:
GRT - Grip Tester
SFH - Surface Friction Tester, High pressure tyre
SKH - Skiddometer BV 11, High pressure tyre
RUN - Runar
VIN - Vertec Inspector
TAP - Tapleymeter

2.6.2 In general there is great uncertainty related to measurement carried out under wet conditions. The snow and ice is then at its melting point. For instance is TAP not accepted under wet conditions. Ref. is made to item 2.7 below for more information.

2.6.3 A measured friction level is associated with the measuring device and can not be used as an isolated number. The acceptable conditions for the measuring devices are:

SKH/SFH:
- Dry snow up to 25 mm.
- Dry compact snow - any thickness
- Dry ice - any thickness
- Slush up to 3 mm.
- Wet snow up to 3 mm.
- Wet ice.

GRT/RUN/VIN:
- Dry snow up to 25 mm.
- Dry compact snow - any thickness
- Dry ice - any thickness
- Slush up to 3 mm.
- Wet snow up to 3 mm.

TAP:
- Dry snow up to 5 mm.
- Dry compact snow - any thickness.
- Dry ice - any thickness.

2.7 SNOWTAM format item H

The table used under item H, with associated descriptions, was developed in the early 1950’s from friction data collected only on compact snow and ice. The friction levels should not be regarded as absolute values and they are generally not valid for other
surfaces than compact snow or ice. Nevertheless it is accepted that friction level may be reported when conditions with wet snow or slush up to 3 mm depth are present and a continuous measuring device is being used. A numerical expression regarding the quality of the friction levels reported in the SNOWTAM can not be provided. Tests show that the accuracy indicated in the table can not be provided using todays friction measuring devices. While the table use numbers with two digits, the tests show that
only numbers with one digit can be of operational value. Utmost caution should therefore be taken when using the reported friction levels, and the use of the table must be based upon the aircraft operators own experience.

vapilot2004

20th Dec 2005, 08:01

The Boeing perspective (previous ppt presentation link) includes a discounting of friction testing equipment results when the runway has more than 2.5cm of Snow. hmmm.....

The Airbus 'Getting to Grips' series on cold weather guide indicates a distrust of the friction measurement results as well. (The French translation gives this one some 'spunkiness in the read' - I give it - - :ok: :ok: - )

I fully expect the NTSB to find more within the data-rich FDR secrets than the already known late reverser deployment.

Perhaps as already mentioned here, newly-formed ice at the moment of landing will become a factor - couple this with what looked like an increased groundspeed just before flare and touchdown - perhaps an added tailwind gust - neither would have been good considering the margins that existed on 31C at the time.

Airbubba

21st Dec 2005, 16:41

From the 'What took them so long to file?' department:

December 20, 2005

Southwest Sued Over Chicago Plane Crash

By REUTERS

Filed at 4:58 p.m. ET

NEW YORK (Reuters) - Two passengers on a Southwest Airlines plane that skidded off a runway earlier this month, killing one person, have sued the airline, Boeing Co. and the city of Chicago, their lawyer said on Tuesday.

The passengers, Mariko Bennett and Stanley Penn, claim to have sustained injuries when the Boeing 737-700 aircraft plunged through a fence-like barrier and onto a busy street, killing a child riding in a car.

Southwest spokeswoman Linda Rutherford said the company had not yet received the lawsuit, which accuses the airline of negligence and conscious disregard for safety.

``The NTSB investigation is ongoing and no cause has been determined yet,'' she said.

Boeing spokesman Jim Proulx said the planemaker had not yet seen the complaint and that in any case it had a policy of not commenting on lawsuits.

SpiralDive

21st Dec 2005, 21:00

Agree with boofhead ,

Where I'm at our company too has adopted a use auto brake for all landings policy, unfortunately I have yet to find a runway turnoff that corresponds with the braking that takes place, LOW is too low and MED is too much too soon for normal dry and wet runways. I am always forced to manually intervene.

D.L

Directly from the Boeing NG Flight Crew Training Manual: Boeing recommends that whenever runway limited, using higher than normal approach speeds, landing on slippery runways or landing in a crosswind, the autobrake system be used

This would seem to allow use of Autobrake OFF when landing on a good day with a long runway, but in the case of this accident the Captain seems to have made a good decision with respect to autobrake useage, despite the apparent management policy for manual braking. At least two of the conditions relevant to Boeing recommending autobrake were present.

The following paragraph from the NG systems manual is also interesting and possibly relevant to this accident and has been mentioned in part before:

The thrust reverser can be deployed when either radio altimeter senses less than 10 feet altitude, or when the air/ground safety sensor is in the ground mode. Movement of the reverse thrust levers is mechanically restricted until the forward thrust levers are in the idle position.

Although it is possible to deploy the reversers any time below 10' RA, it would not have been immediately possible if the thrust levers weren't completely closed before attempting reverser deployment.

flybubba

22nd Dec 2005, 01:45

Interesting discussion about whether to apply back pressure on the yoke to improve braking. I don't think that this would work. I believe the center of gravity and center of lift are close to where the main gear are mounted. Once on the ground, I think the main gear wheel/ground contact point is just a pivot point about which the tailplane forces work. At this point, changing the tail plane force can work two ways: If you apply foward force on the yoke, you reduce the main wing AOA, reducing lift, increasing the main gear WOWs and thus increasing friction. IF you apply back force on the yoke, you are increasing AOA, lift, thus reducing WOW and friction force. In addition you reduce the nosewheel force thus reducing steering effectiveness. I think this idea is not correct.

OK, upon further thought here are things to ponder:
The question is where is the center of lift and center of gravity relative to the main gear footprint. By changing the tailplane force here is what happens: The main wing lift is changing. This does two things. There is a change in the lift force vector, but there is also a change in the torque due to this lift force vector acting about the main wheel footprint. Anyone care to comment?

RatherBeFlying

22nd Dec 2005, 02:52

This is how I see the basic physics:

Once you are on the ground, back stick produces a couple about the main gear and downforce on the tailplane which adds to the weight on the main gear.

Of course back stick produces a subtraction of downforce at the nosewheel, but that is more than countered by the couple and downforce produced by braking at the main gear. Reverse from engines below the wing will also produce another couple about the main gear that adds downforce to the nose gear.

So back stick, once reverse and braking are applied, has to work against considerable forces that are not present in the air before the nosewheel will come up. Until the nosewheel starts coming up, the AOA remains constant.

The physics behind Belgique's suggestion of back stick during braking looks perfectly sound to me.

What I do not so far see is any manufacturer data on its effects and limitations which can then be passed on to the crews.

Airbubba

22nd Dec 2005, 02:52

>>Any opinions on the above SOP in relation to the topic?

Uh, this is pretty much boilerplate everywhere I've ever worked. What do you propose? Ducking under a couple of dots to hit brick one?

Airbubba

22nd Dec 2005, 04:01

>>BTW, Last time I checked the approach ended at the DH/DA. Beyond that landing is a visual maneuver.

May I presume you don't fly large airplanes for a living? Like I said...

Ysatis

22nd Dec 2005, 04:19

... where do you come from folks. If you think worth talking about an accident that is still under investigation, as pilots or "professional pilots", humm questionnable. That you start wondering about physic laws rather than simply applying manufacturer recommendations, humm questionnable. but please, stop flying, but if you happen to be involved in an accident, "smarter than test pilots" individuals might do silly things to you without even knowing what they're talking about.
KR

XL5

22nd Dec 2005, 05:38

"On runways served with an electronic glideslope, maintain on or above the glidepath until transitioning to flare."

Any opinions?

Since you asked.

A threshold crossing heigt of 50 feet on a 3 degree glide slope puts the Battle of Hastings (1066 ft of runway) behind the aircraft at the touchdown point with no flare. Note that this figure assumes holding a constant sink rate, say about 700fpm to impact - more of an arrival than a landing.

The heavy dinosaur I flew was best handled under certain circumstances by being one dot low on GS with no more speed than Ref (and hopefully slowly decaying) when crossing the threshold. True, it isn't written that way in the book but it's equally true that short slippery runways are just one example in which following the book will get you into trouble.

Holding the GS at Ref +5 isn't always the best strategy.

Dagger Dirk

22nd Dec 2005, 10:41

RatherbeFlying said
the basic physics:

Once you are on the ground, back stick produces a couple about the main gear and downforce on the tailplane which adds to the weight on the main gear.

Of course backstick produces a subtraction of downforce at the nosewheel, but that is more than countered by the couple and downforce produced by braking at the main gear. Reverse from engines below the wing will also produce another couple about the main gear that adds downforce to the nose gear.

So back stick, once reverse and braking are applied, has to work against considerable forces that are not present in the air before the nosewheel could come up. Until the nosewheel starts coming up, the AOA must remain constant.

The physics behind Belgique's suggestion of backstick during braking looks perfectly sound to me.

Looks perfectly sound to me too.

The next step is for the manufacturer(s) and FAA to validate it, measure it and advocate it. Then maybe we will see fewer airplanes going off the end.

However it might need to sit on the NTSB's "list of desired fixes" for a few qualifying years first.

jondc9

22nd Dec 2005, 13:24

OK

any pilot will tell you that the ILS glideslope is virtually sacred in bad weather conditions. Regulations do allow for descent below the glideslope when required for a safe landing.

somewhere around the middle marker...but MDW doesn't have a middle marker.

I will tell you right now during good weather many pilots "duck" the glideslope to land closer to the threshold of the runway.

BUT on a dark, snowy, stormy night you simply must stay on the glideslope until the wheels are over the concrete.

SADLY, I think that southwest procedures and calculations may assume that you land at the displaced threshold...this would have given the extra 800 odd feet to stop.

the trouble with that theory is that you coudn't see the threshold and the glideslope leads you almost 1000' down the runway from there. ON top of all of that the concept of flare delays touchdown. By the way, an airplane can handle a firm touchdown to about 600fpm...more than that requires a "hard landing inspection".

the chicago tribune is reporting today that southwest had a visibility wavier to allow approaches with 1/4 mile LESS visibility than
published.

a mistake if you ask me. while it is one thing to land in lower visability with calm or head wind on a good runway, add ICE, and tailwind and 3 strikes your out!

jon

flybubba

22nd Dec 2005, 15:07

Rather be flying:
I think your point about aft yoke working as long at the nose wheel stays down is important. You must assume that the nose wheel strut is compressed and that it doesn't change for aft yoke to work. If the nose strut compression changes at all, the AOA will change, thus working against you.

regards,
flybubba

RatherBeFlying

22nd Dec 2005, 17:38

fb

I suspect that during heavy braking and reverse there is a surplus of force to keep the nosewheel strut fully compressed and the AOA constant.

Until back stick reduces that force below the force to keep it fully compressed, it ain't gonna come up and the AOA will stay put.

Certainly the downforce on the nosewheel strut varies with a/c type, weight, cg, speed, trim/elevator position, spoilers, braking couple, reverser couple.... those with the data might be able to work out the moments and couples and put it into tables. This data may or may not be in the simulator software -- it would be interesting to know.

The institutional question is what does / can a line pilot do with this technique until the manufacturer, authorities and airlines work it into the SOPs and distances.

I don't really think this is a technique that should be used by dispatch to shave margins further. I'd rather keep it in the back pocket for when something extra is needed to stop before going off the end because the runway ain't what I was expecting.

regards,
rbf

JW411

22nd Dec 2005, 18:34

I don't know if this has anything to do with the price of butter but I do remember an overrun accident at LAX involving a DC-10 which abandoned take-off at a fairly high speed.

The SOP in such an event was for the PNF to apply stick pressure "forward of neutral" to ensure good nosewheel contact.

On this occasion, the PNF stuffed the control column fully forward into the instrument panel (a matter of interpretation)?

The horizontal stabiliser on the DC-10 had the same wing span as a DC-3. This had the result of raising the tail to the extent that the main gear trucks were lifted off the ground initially and so the braking action was considerably less than the performance engineers had imagined.

You will be astonished to learn that the aircraft ended up in the overrun and an emergency evacuation was the result. Fortunately I believe there was only one casualty.

I therefore have found it valuable to brief my F/Os exactly where I want them to put the control column vis a vis fore and aft as well as into wind etc for every take-off or on landing when they take the control column on a rejected take-off or at 80 knots on landing.

Clarence Oveur

22nd Dec 2005, 18:36

Why is this then not more prominently featured in the training material from the two major manufacturers?

JW411

22nd Dec 2005, 18:51

Well I seem to remember that advice did indeed come from MDC but then they were absorbed into Boeing so maybe you should ask the question of them and Airbus?

barit1

22nd Dec 2005, 19:41

ysatis sez: That you start wondering about physic laws rather than simply applying manufacturer recommendations, humm questionnable.

I think this discussion is more along the lines of observing differences in mfgr's recommendations, and reconciling these with Newtonian physics.

Of course - if you merely want to fly "by the book" and ignore the physics, my best to you... :ugh:

Dagger Dirk

23rd Dec 2005, 03:17

I don't really think this is a technique that should be used by dispatch to shave margins further. I'd rather keep it in the back pocket for when something extra is needed to stop before going off the end because the runway ain't what I was expecting.

Except for a few hold-outs who apparently:

a. Haven't been able to reconcile the aerodynamics

b. Slavishly adhere to manufacturer recommendations only

c. Can't believe that (if it's a fact) somebody would've been recommending it already

OR

d. prefer a free-floating control column under braking as a safer form of non-commital (with concessions for some aileron into any crosswind)

...............then we have some believers.

But I personally wouldn't leave it until the end was looming fast BEFORE deciding to adopt this braking technique (i.e. suck the stick back into my gut and expect a miracle turnaround in my stopping power). I'm instead guessing that it's best used early and throughout - to avoid those "looming situations"

dallas dude

23rd Dec 2005, 03:28

Airbubba,

quote..."Uh, this is pretty much boilerplate everywhere I've ever worked. What do you propose? Ducking under a couple of dots to hit brick one?"

Err...don't you mean "shingle one?".

Cheers, dd.

Ignition Override

23rd Dec 2005, 05:19

What about the fact that the Midway Controllers only allowed approaches with a tailwind to a snow-covered runway?

If this was true, then it made no sense, that the airport could not be "turned around", so to speak.

Would an aircraft need to declare an emergency in order to land at MDW (on snow) with a headwind?

It makes no sense that the only option was to divert to nearby O'Hare Airport-but it was a good option, as long as they had decent (jet), new braking action reports.

How will the NTSB factor the MDW tailwind only operation into the cause of the accident?

PaperTiger

23rd Dec 2005, 16:53

If this was true, then it made no sense, that the airport could not be "turned around", so to speak.When 14R/14L are in use at KORD (O'Hare) which they were at the time, KMDW 13C is unavailable due to approach conflicts.

Shore Guy

23rd Dec 2005, 21:30

Airbubba

23rd Dec 2005, 23:26

>>Various news media in the states are reporting that the approach and landing were accomplished under an FAA Waiver (published mins 3/4 - weather was at 1/2).

I think they had at least RVR 4000 according to the wx sequences earlier in this thread, that would give them published mins on a RW 31C ILS without a waiver I believe.

Shore Guy

24th Dec 2005, 00:07

Doesn't SW have HGS in some of their aircraft?

Airbubba

24th Dec 2005, 00:35

>>Doesn't SW have HGS in some of their aircraft?

Yes, over 400 Southwest planes have HGS, don't know about the MDW plane.

SeniorDispatcher

24th Dec 2005, 00:58

Various news media in the states are reporting that the approach and landing were accomplished under an FAA Waiver (published mins 3/4 - weather was at 1/2).

Does anyone know specifically which waiver authorized this?

Back in January of 2003, ATA (the airline, not the industry group) got FAA approval for an ILS-Z to 31C taking the minimums down to 5/8SM RVR 3000 by virtue of the HGS they had installed on their 738 and 753 aircraft. SWA later got the same authorization, since they also were starting to install HGS...

If I recall correctly, the guy at ATA who led the charge on developing the new procedure for ATA had been recently been hired away from FAA. I'm sure that Googling various terms would probably result in a press release...

Ignition Override

24th Dec 2005, 03:29

Paper Tiger-yeah, that looks familiar. But with those weather conditions, could they not vector planes with different intercept angles, or give a go-around from ORD 14R with an immediate right turn etc?

Tanker

24th Dec 2005, 16:50

The landing performance penalty is only in the AIII mode. You can do the ILS-Z at MDW in the IMC mode with no landing penalty. That is because the AIII mode is the only mode that has a flare command.

Mad (Flt) Scientist

24th Dec 2005, 18:58

As one of the "holdouts", may I just point out that the recommended procedure on many of my company's products is to apply some (not full) forward stick force to ensure that the nosewheel does not lift when braking and applying reverse thrust. Those people convinced that they can apply back force without raising the nose at all can perhaps ponder this piece of advice - which has been validated during several flight test programmes and is not in the recommended procedures because we were bored and wanted to fill some white space in the books.

Explaining post-accident why you decided to do something different to, or contrary to, the manufacturer's recommendations would be, I suspect, an unpleasant experience. Especially if it were shown that your inventiveness had contributed to the event. (For example, you're probably postulating this technique for contam runways; what about with a xwind component? Won't be fun if you start to unload the nosewheel and lose steering. Going off the side of the runway is no better than off the end)

Airbubba

24th Dec 2005, 20:02

>>As one of the "holdouts", may I just point out that the recommended procedure on many of my company's products is to apply some (not full) forward stick force to ensure that the nosewheel does not lift when braking and applying reverse thrust.

I have to agree, this is what most of us do in the real world...

jondc9

24th Dec 2005, 23:55

I had the great pleasure of knowing a very fine pilot named Bill Giannotti. He used to teach pilots how to fly B17's and B24's during ww2.

He was giving me my checkride for CFI way back when and the subject of pulling back or pushing forward came up to get best braking.

its as simple as this. if you are flying a big modern jet, get on the ground, get your spoilers out and push forward a bit, reverse and brakes. having flown a jet that when selecting reverse the nose would come up ,this is good advice.

if you are flying a light single or twin (think piper arrow or seneca) get down, retract flaps and pull back a bit.

I have also flown the 737 (into midway too) I would plant it, make sure spoilers deployed, keep the nose down and get on brakes and reversers pronto especially that snowy night. IF YOU ARE NOT STOPPING firewall reverse (risking some damage to engines, compressor stalls, even kicking up sooooo much snow you might not see) and hold brakes until the anti skid cycles and keep on them to a complete stop.

Normal stopping has reverse out and not on the brakes till about 100 knots, increase brakes as you bring the engines to idle, be sure you are at idle before cancelling reverse.

sadly, there are visual illusions that might make a pilot think he is slowing down, when this happens a pilot MIGHT, repeat MIGHT cancell reverse too early.

sometimes you have to keep reverse till you are going backwards ;-)

jon

tribo

2nd Jan 2006, 09:20

An "old" update at this link:

http://abcnews.go.com/Business/FlyingHigh/story?id=1412384

handflying

2nd Jan 2006, 10:45

quote from jonDC9:"sometimes you have to keep reverse till you are going backwards ;-)"

Sorry jon but effectiveness of reverse at low speeds is greatly reduced (don't know if you remember formula of thrust produced by reverse=depends on the amount of ramair through engine and thus speed). Below 60 kts thrust is still something but at taxi speed as good as nil so this was a little exaggerated I think. Also you could suck in gasses having been burnt allready...

BOAC

2nd Jan 2006, 10:53

hand - slightly misleading post? - the advantage in keeping reverse in to a stop if needed is that you are, apart from producing SOME braking effect, removing most elements of forward thrust which can spoil your day even more. In an emergency, ingesting exhaust gases is a minor consideration put against ingesting mud, grass or worse.

handflying

2nd Jan 2006, 11:00

BOAC: taxi speeds are not more then 20 kts.

At 10 kts it doesn't take a lot of braking energy to stop the AC with brakes if you are not in the grass emergency yet...If it really is an emergency your tires should be by that time exploding.

BOAC

2nd Jan 2006, 12:41

At 10 kts it doesn't take a lot of braking energy to stop the AC with brakes if you are not in the grass emergency yet...If it really is an emergency your tires should be by that time exploding.- don't wish to drag this out into pedantry, but the thread is about an incident where the brakes were probably almost ineffective so personally in such a situation I would like to improve my chances of stopping. Also, if as you say, you fly 767, you will have noticed the small 'kick forward' as you deselect reverse at low speed? Hopefully, also, MY tyres will not 'explode' until a little while after I stop:)

handflying

2nd Jan 2006, 13:17

With all due respect this is about the efficiency of using reverse at taxi speeds less then 20 kts: no there is no feeling of forward thrust on the 767when cancelling reverse at 10 kts eg (maybe it has more inertia then a 737-don't know because never flew 737). Also I will read boeing FCTM again but almost sure that it says reverse should be cancelled before reaching idle in NORMAL ops.

Point is: reason for the overrun is NOT lack of reverse thrust at speeds less than 20 kts even if you do what you can in an emergency!! Yes you can use it if you think it helps!!But I think it is too late by that time!!

Anyway if that is the way moderators consider appropriate to respond to a subscribers opinion very willing to unsubscribe. Good luck and happy landing.

jondc9

2nd Jan 2006, 13:31

Dear HAND:

Regarding reverse thrust at low speeds:

You are talking about taxi speeds below 20 knots. Hooray. The southwest airliner went off the end of the runway at more than 40 knots.

I mentioned keeping reversers extended and developing thrust because there is a certain visual illusion which makes pilots think they are stopping when they are not doing so. said pilots often cancel reverse early with the engines still producing significant thrust. when canceled the thrust is no longer reversed and accelerates the plane. IF YOU HAVEN'T ever felt this on the 767 or any plane either you are: allowing the engines to come to idle prior to cancelling reverse (GOOD FOR YOU) or you haven't actually flown an airplane with reverse.

IN THE simulator ( and I am not talking microsoft) the rule of thumb is to keep reverse until the image in the sim shows you are going backwards. AS silly as this may sound to the uninitiated, it keeps you on the runway, which is the name of the game.

OH and by the way, I have seen perfectly good landings on snow covered runways only to be spoiled by slipping on the taxiway. The only saving grace was REVERSE at speeds below 10 knots.

If you have flown the 767, I encourage you to read, "Handling the Big Jets" by DP Davies (former certification test pilot for UK's CAA). Even he says to keep reverse in if there is doubt about stopping on the runway and not to worry too much about gas ingestion.

So, HAND, I hope I have made myself clear.

jon

handflying

2nd Jan 2006, 14:24

Completely agree with you jon:in extreme adverse conditions (poor braking action, snow...) you can use reverse thrust at speeds less then taxi speeds and more interesting yet as you say on slippery tawiways because very true indeed I have seen people sliding as well.

So I can agree with the "sometimes" you can use it till going backwards; also probably you are more confronted with heavy winter conditions then we (rarely) have in Europe. (Still never felt fwd thrust when cancelling reverse at 10 kts, even when light; theory is right though).

Thereby ending this parenthesis as it is not the reason why it went off the end of the rwy at 40 kts.

jondc9

2nd Jan 2006, 14:36

HAND:

of course I agree with you that in normal situations one would not hold reverse till going backwards. Thank you for clarifying this. But on that sad night in Chicago, I hope that the crew had "firewall reverse". You may not have heard that it took 18 seconds after touchdown to properly select reverse!

I am sure you are enough of a pro to properly cancel reverse and you probably have not felt the forward "kick" as some have called it.

I have flown into Midway airport on dark and stormy nights...even doing a circling approach while snowing one night in a 737 (our company requires circling at or above minimum VMC condidtions) but it was still tough.

I hear the wx in europe can be tough though!

jon

tribo

23rd Jan 2006, 13:59

From USA Today:
www.usatoday.com/news/nation/2006-01-22-runway-warnings_x.htm
http://www.usatoday.com/news/nation/2006-01-22-runway-skids_x.htm

d192049d

23rd Jan 2006, 16:12

Handflying....example of the truth disproving the rule

Whilst not directly related to the aircraft type involved I have personally witnessed the effective use of Reverse at slow taxi and from standstill. Both cases were TU154's one to do a "three point turn" at EGBB in te days before parallel taxi ways and one was to move off blocks when no tow bar available.

Perhaps todays modern jets are less able??

innuendo

23rd Jan 2006, 17:17

Handflying, I would suggest that there is still a fair bit of reverse effect even at a standstill. I say this from experience having done a lot of powerbacks off the gate in the 727. Our company also used powerback on the DC-9 fleet for some time.

westhawk

26th Jan 2006, 03:15

Bonger:

Thanks for posting that letter From SWAPA. Well written in that it provides valuable information which can be used as an aid in decision making by the SWA pilots. Forum readers and others may benefit as well. All while avoiding the subject of any investigative conclusions. Kudos to the safety commitee for getting this out. It was the right thing to do.

Westhawk

BOAC

26th Jan 2006, 07:30

Forum readers and others may benefit as well- well, I certainly will. Thanks to the team for some useful insights.

tribo

26th Jan 2006, 22:30

From SWA Pilots Association Winter WX Safety Alert
The formula for these equations appears to have come from a 1961 Convair 880 test that was conducted by the FAA.
These “mythical” test are published in the:
Final report, Project No. 308-3X.
Runway slush effects on the takeoff of a jet transport
May 1962
FAA, System Research & Development Service, Experimentation Division
Atlantic City, New Jersy, USA
The reports summary:
The extent and damage and decrease in takeoff performance of a jet transport from encounter of runway slush was determined from full-scale tests with a Convair 880 Model 22M aircraft.
Tests were conducted on a slush-covered section of a 10,000.foot runway at depths of 0 to 2.0 inches and velocities of the order of 80 to 160 knots.
Retardation forces were calculated from the deceleration of the aircraft as it coasted through the slush test area at idle power. Position and velocity of the aircraft were determined by tapeswitches and phototheodolites. Deceleration was determined by an airborne accelerometer. Wheel slippage for all ten landing wheels was obtained from the antiskid braking system. Extensive photographic coverage on the ground, in the air, and from the aircraft provided the slush spray-pattern data. The retardation forces measured from the deceleration data were considerably greater than those predicted from earlier wheel and tire drag tests and theoretical studies which neglected the factor of slush spray impingement and aquaplaning. Impingement of slush against the aircraft and landing wheels contributed significantly to slush drag forces. Aquaplaning occurred and resulted in reduced slush drag forces on the test aircraft at velocities above 120 knots.
An analysis was made of the various factors contributing to the total slush drag force measured on the aircraft. Future areas of study and research are indicated to develop generalized slush formulas for other types of aircraft. Physical damage to the aircraft from slush impingement was slight; however, accumulation of slush in various recessed areas indicated the possibility of an operational hazard with subsequent freezing after takeoff and climb to altitude.
Test program:
The test program was conducted at the National Aviation Facilities Experimental Center, Atlantic City, N. J., from September 15, to October 8, 1961, with braking tests being conducted subsequent to slush drag tests. Results of the braking tests are contained in a seperate report:
J.J. Shrager, Vehicular Measurement of Effective Runway Friction, FAA/ARDS Report, June 1962. (Can anyone provide me with that report?)
The ice used for slush was delivered to the test strip in 300-pound blocks by insulated trailer truck vans of 20-ton capacity. A crusher-slinger machine was attached to the rear of the van during the slush-laying operation. As the van moved along the test strip, the 300-pound blocks of ice were fed to the crusher in a continuous operation. A stream of crushed ice was discharged from a nozzle and sprayed onto the test strip. To achieve a more uniform depth of slush, temporary wooden forms were used to divide the 1000-foot test bed into four long narrow strips. The depth of the slush was regulated to the height of the forms by dragging a levelling board across the top of the forms. To speed up operation, eight crushing machines, with a total rated capacity of 400 tons of ice per hour, and eight crews were used for laying slush.
.
.
The time required for slush laying varied from 25 to 90 minutes, depending on the depth and length of the slush bed. The maximum depth of snow/ice laid for a test was approximately 3.0 inches over the 1000-foot test area, and 1.5 inches over the 3000-foot test area.High ambient temperatures made it necessary that slush-laying be completed rapidly to reduce the amount of ice melting prior to the test run. For this reason, the slush-laying was completed before sunrise when air temperature and disturbance were minimum.

The depth and desity of slush were obtained frome samples taken at fixed stations over the entire area of the slush bed. The maximum nuber of samples of slush taken was 36.
.
.
Sample points were located along the center of the runway and 9.5 feet to each side of the centerline.
Tests:
Testbed 1000ft long.
Deceleration test runs (100 – 140 Knots)– speed entering and exiting the testbed are given. Slush depth is an average of 6 readings.
No. 1 – 25.09.1961 – 111.6 kt – 107.5 kt – Dry condition
No. 2 – 25.09.1961 – 111.9 kt – 107.8 kt – Dry condition
No. 3 – 26.09.1961 – 125.8 kt – 120.7 kt – Dry condition
No. 5 – 28.09.1961 – 129.8 kt – 125.2 kt – Dry condition
No. 7 – 04.10.1961 – 112.3 kt – 108.1 kt – Dry condition
No. 8 – 26.09.1961 – 115.7 kt – 101.8 kt – 0.90 inches slush
No. 8A – 27.09.1961 – 115.4 kt – 101.5 kt – 0.85 inches slush
No. 8B – 09.10.1961 – 115.8 kt – 102.4 kt – 1.21 inches slush
No. 9 – 29.09.1961 – 130.5 kt – 114.0 kt – 1.15 inches slush
No. 11 – 09.10.1961 – 115.8 kt – 97.3 kt – 1.48 inches slush
No. 12 – 01.10.1961 – 134.9 kt – 122.1 kt –1.08 inches slush
No. 14 – 29.09.1961 – 119.2 kt – 93.0 kt – 2.03 inches slush
No. 15 – 01.10.1961 – 136.1 kt – 116.3 kt – 1.61 inches slush
No. 19 – 06.10.1961 – 115.0 kt – 98.2 kt – 1.34 – 1.43 inches slush
No. 20 – 05.10.1961 – 101.4 kt – 88.9 kt – 1.25 inches slush
No. 20A – 06.10.1961 – 97.5 kt – 75.4 kt – 1.97 inches slush
Deceleration test runs – 160 Knots:
No. 4 – 27.09.1961 – 153.8 kt – 149.3 kt – Dry condition
No. 10 – 05.10.1961 – 157.6 kt – 149.7 kt – 0.92 inches slush
No. 13 – 05.10.1961 – 156.6 kt – 143.3 kt – 1.14 inches slush
Acceleration and takeoff tests runs
No. 17 – 07.10.1961 – 100.1 kt – 130.9 kt. – 1.14 inches slush in the first 1500 ft. of the 2960 ft. long testbed. Rotation and liftoff outside the testbed.
No. 18 – 08.10.1961 – 127.9 kt – 129.3 kt – 1.38 inches slush. Testbed 1460 ft long. Rotation and liftoff inside the testbed.

jondc9

27th Jan 2006, 16:12

Will the FAA react?

I hope so!

========

************************************************************
NTSB PRESS RELEASE
************************************************************

National Transportation Safety Board
Washington, DC 20594

For Immediate Release: January 27, 2006 SB-06-06

************************************************************
NTSB URGES FAA TO PROHIBIT AIRLINES FROM USING THRUST
REVERSER CREDIT IN DETERMINING RUNWAY STOPPING DISTANCES

(Safety Recommendation A-06-16)
************************************************************

WASHINGTON, D.C. - The National Transportation Safety Board
today urged the Federal Aviation Administration to prohibit
airlines from using credit for the use of thrust reversers
when calculating stopping distances on contaminated runways.

The urgent safety recommendation is the result of
information learned by the NTSB during its investigation
into a fatal runway overrun in Chicago last month.

"We believe this recommendation needs the immediate
attention of the FAA since we will be experiencing winter
weather conditions in many areas of our nation for several
more months to come," NTSB Acting Chairman Mark V. Rosenker
said.

On December 8, 2005, Southwest Airlines flight 1248, a
Boeing 737-7H4, landed on runway 31C at Chicago Midway
Airport during a snow storm. The aircraft failed to stop on
the runway, rolling through a blast fence and perimeter
fence and coming to rest on a roadway after striking two
vehicles. A 6-year-old boy in one of the automobiles was
killed.

While approaching Chicago on a flight from Baltimore,
the pilots used an on-board laptop performance computer
(OPC) to calculate expected landing performance.
Information entered into the computer included expected
landing runway, wind speed and direction, airplane gross
weight at touchdown, and reported runway braking action.
The OPC then calculated the stopping margin. Depending on
whether WET-FAIR or WET-POOR conditions were input, the
computer calculated remaining runway after stopping at
either 560 feet or 30 feet.

Both calculations were based on taking a stopping
credit assuming engine thrust reverser deployment at
touchdown. Flight data recorder information revealed that
the thrust reversers were not deployed until 18 seconds
after touchdown, at which point there was only about 1,000
feet of usable runway remaining.

The FAA does not allow the use of the reverse thrust
credit when determining dispatch landing distances; in fact,
historically decreases in stopping distances due to thrust
reverser deployment were used to offset other variables that
could significantly degrade stopping performance. However,
the FAA does permit thrust reverser credit for calculating
en-route operational landing distances for some transport
category aircraft, like the 737-700 series, but not for
others, like the 737-300.

If the thrust reverser credit had not been allowed in
calculating the stopping distance for flight 1248, the OPC
would have indicated that a safe landing on runway 31C was
not possible. "As a result," the Board said in its
recommendation letter, "a single event, the delayed
deployment of the thrust reversers, can lead to an unsafe
condition, as it did in this accident."

Although the recommendation would prohibit the thrust
reverser credit on all runways, its practical effect would
be felt on planned landings only on contaminated runways,
which is when the credit is included in stopping distance
calculations.

Therefore, the Board is recommending that the FAA:

Immediately prohibit all 14 Code of Federal
Regulations Part 121 operators from using the reverse thrust
credit in landing performance calculations. (A-06-16)
(Urgent)

A copy of the recommendation letter may be found at
the following link on the Board's website:
http://www.ntsb.gov/recs/letters/2006/a06_16.pdf

-30-

westhawk

27th Jan 2006, 19:41

Will the FAA react?
I hope so!

Indeed. If only it were that simple. Somebody had to advocate for this procedure of determining required landing distance while taking credit for the effect of thrust reversers. Boeing and Southwest would both have had to be involved in getting approval to take credit for reverser use. To end that advocacy now may be perceived as admitting a mistake. That is something that the companies involved may be advised by legal council to be wary of, considering the pending litigation. In that the FAA gave their approval to use this procedure, it will place them in a similar conflict of competing interests. Do the right thing or protect yourself against the repercussions of your past actions?

The landing distance calculation used appears to have been pretty accurate. Had the reversers deployed 10 seconds earlier, we would probably not be discussing it. Most of the time, nothing bad happens because things go nearly according to plan. Here, they did not. The question lies in whether or not it is an acceptable risk for an airliner to land when a single error or failure of any of the stopping system components is likely to result in exceeding the ALD. At the time of dispatch, under current rules, landing distances must be factored to provide an additional safety margin. While it may be reasonable to allow the elimination of landing distance factoring if conditions at the airport change while enroute, allowing unfactored landing distance to be used WITH credit for reverse thrust removes all remaining built in margin for error or failure. Regardless of what actions the FAA does or does not take, under current rules, PICs will still have to decide whether to land at the scheduled airport or divert. I would tend to believe that the diversion option will now be given greater consideration by airlines and their crews. At least for awhile. And if airport operators are unable to keep their runways free of contamination for any reason, the airlines may find it prudent to consider that before they dispatch.

Taking advantage of the built-in loopholes in the regulations may be seen as either an allowable business cost-control measure or an invitation to a mishap. Depends upon the outcome and which table you sit at in the courtroom. In reality, it is both. Obviously, unnecessary diversions are not desirable from a business standpoint. Nor are accidents. Even the bean counters should feel they have some safety responsibility in the performance of their duties just as all other employees have some fiscal resposibilities in the performance of their duties. Setting the priorities is a leadership function which requires an intimate knowledge of the factors involved in order to implement a reasonable and prudent policy.

In this particular case, at least one thing did not occur as planned for and the outcome is now history. The investigation of this accident will answer many of the questions about how it occured. But one question will still remain: How much safety margin is enough? In my personal opinion, the NTSB recommendation posted above is reasonable and prudent. Operators should consider adopting it immediately regardless of whatever actions the FAA does or does not take in this matter. Any worries about competitive disadvantage may be offset by considering the potential consequences of a similar accident in the future. The next one would be widely considered to have been even more "foreseeable" than this one. I hope all involved parties make the right decision.

Best regards,

Westhawk

punkalouver

28th Jan 2006, 00:03

jondc9

28th Jan 2006, 00:12

Tanker

28th Jan 2006, 00:30

midway is an odd little airport. if you flew the ILS Glideslope perfectly to touchdown you would have 4927feet of runway remaining. Even the test for a commercial pilot cert. requires you to show that you can land within 200 feet of your selected spot.
they landed longer than that, plus a bounce of unknown distance.
also note that the ILS OM is much closer to the runway than most.
j
From what the NTSB is saying there was no bounce, the landing was firm. Also the FAA requires 121 aircraft when on glideslope to land within the first 1000 feet. From what the NTSB is reporting they landed within 750 feet. So there was no long landing or bounce.

jondc9

28th Jan 2006, 00:52

Ignition Override

28th Jan 2006, 05:44

A few years ago a DC-9 slid off of the end of the runway at Traverse City, Michigan.
From what I read about it, the airport either had no current braking action readings (Saab, Tapley, Bomonk etc) and gave the flightcrew information which was incorrect. Based on the information which was given, if it had been accurate, the plane would have had a much better chance of stopping before the end.
The flying pilot landed (following a non-precision approach) well within the required touchdown zone and on speed. The Captain was not faulted-the airport was!
Years before that, a crew had a Captain on board who had never flown the DC-9 as First Officer, and was new in the left seat: nice combination (and no automation :uhoh: ). The Grand Forks (N.D.) Airport was supposed to spray chemicals on the runway and then sand. But NO chemicals were sprayed-only some sand was thrown onto either thin ice or snow. The rudder lost effectiveness because of tail-mounted engines and the plane slid sidways into the grass, and some crosswind might have been involved.
Be aware that the airport information might be far from accurate.

In the era of not just airline, but government budget cuts, anything is possible.

Did the Southwest crew ask Midway Approach for an approach with a headwind component?

westhawk

28th Jan 2006, 07:37

Woukd you consider it to be two things did not occur as planned. 1. delay in reverse thrust. 2. Landing 2000 feet down the runway?

punkalouver:

The delay in achieving reverse thrust was, in my estimation, the most critical factor that did not go according to plan. The NTSB update of Dec 15, 2005 stated that touchdown occurred with aproximately 4500' of runway remaining. While this is 2000' less than the total runway length, it is only 1300' less than the available landing distance due to to the 696' displaced threshold. This means that assuming that they touched down with 4500' remaining, they were about 1300' beyond the landing threshold. Considering the low ceiling and visibility conditions that were in effect at the time of the approach, it would have been prudent to stay on glideslope all the way to roundout. Even if the aircraft were flown on to the runway with no roundout at all, (That was no landing, that was an ARRIVAL!) it would impact with the runway abeam the G/S antenna. I think it's safe to say that the G/S intercepts the ground at a point somewhere beyond the landing threshold of 31C. Perhaps someone who has access to Jeppview from home could post the distance available beyond glideslope. This distance minus the NTSB's estimated 4500' remaining at touchdown would represent the distance beyond the glideslope at which the aircraft touched down. This may not necessarily be as excessivily long of a landing as it first appears. Rather, it is about what one would expect if the glideslope were followed to around 50', followed by partially arresting the decent to an acceptable rate prior to touchdown. Especially with an 8 kt tailwind component. Even though dispatch and the laptop tool aboard the aircraft agreed that this landing was within limits, it was just barely so and consequently, if anything went wrong....... Well, it seems it did, at least in the form of not getting T/R deployment until 18 secs after touchdown for whatever reason. Any distance beyond the G/S antenna that the touchdown occurred would also contribute. To what extent that is a factor, I do not know. The investigation continues.

Best regards,

Westhawk

Danny

28th Jan 2006, 11:12

What I find quite disturbing is the following from the NTSB statement/recommendation (my emphasis):...The OPC then calculated the stopping margin. Depending on whether WET-FAIR or WET-POOR conditions were input, the computer calculated remaining runway after stopping at either 560 feet or 30 feet.Either of those two numbers would give me great cause for concern. To expect such a short distance of runway to be remaining under normal good weather conditions, never mind those being experienced and forecast at the time would leave me with a serious doubt about using that runway in anything except a no-option emergency.

No doubt there are other pilots on here who have a bit more faith in their own piloting skills and accuracy that will have a go at me for being so cautious but we do this job in the knowledge that we will be minimising the risks as much as possible. If there is a tailwind component we factor everything by 150%. The touchdown zone is not the runway threshold but much further down the runway. We have contingency and alternate fuel in case of problems. Shouldn't we also factor in the amount of runway that should be left after coming to a complete stop should be something similar to the amount we leave behind us on touchdown? By all means, we can use the total amount available but we should only ever plan to use the total amount of runway available in an emergency and we have no alternative runway available within the limits of fuel remaining.

Safety Guy

28th Jan 2006, 11:50

Spot on, Danny. I too was befuddled by the notion that anyone would try to land a perfectly good airplane under those circumstances. No doubt some of that is a function of culture (Southwest's emphasis on OTP), and some of it may end up being that they were influenced by the success of the preceding flights whose pilots got lucky and made it in.

As is typical in accident investigation reports, the investigators will no doubt look for ways to address the causal factors through changes to the regulations. It will be very interesting to see how the final report addresses the legalities involved in this case. I wonder if they will require similar "buffering" to be applied to actual landings on contaminated runways as many regulators do when flight planning is done.

Willit Run

28th Jan 2006, 12:39

Early on in 2005, there were 2 747-200's that over ran runways due to snow contaminated runways. Both were short runways. Thats 3 in one year!
We all like to complete the trip as planned, but at some point, we must say,
" Ain't hapenin today"; or "We'll take another runway thank you" or " We'll be diverting, have a nice day"
Lets look at past history along with the runway data, then make your decision to land.
If it can happen to someone else, it can happen to you!

canyonblue737

28th Jan 2006, 13:24

Very interesting post. To quote...
"In this particular case, at least one thing did not occur as planned for and the outcome is now history. "
Woukd you consider it to be two things did not occur as planned. 1. delay in reverse thrust. 2. Landing 2000 feet down the runway?

they did not land 2000 feet down, they landed 1300 ft from the displaced threshold and 300 ft beyond the 1000 ft mark that the GS brings you to.

sounds like a spot on touchdown zone landing to me, some could argue you should duck under but that isn't SOP and the landing numbers are based on landing in the touchdown zone which they did.

Tanker

28th Jan 2006, 14:49

dear tanker:
I have seen other NTSB reports stating that the plane "bounced" on landing. Reported by the PILOTS.
if you have other data, please post.
Also 4927-750= 4177 feet remaining to stop. that is not alot. especially when thrust reverser deployment was delayed by 18 seconds to a point with only 1000' remaining.
And if thrust reverser deployment was delayed because thrust levers were not at IDLE STOPS, then the plane's engines were developing forward thrust at IDLE PLUS power.
j
The NTSB reports I've seen about the landing being firm and with no bounce were on the SWAPA pilot only website. All indications are that the thrust levers were at idle and the reversers should have deployed. The reason they didn't is still being investigated. I'm sorry that I'm not computer literate enough to provide the link:ugh:

jondc9

28th Jan 2006, 18:50

some questions about runway 31 center and there answers:

4927' remain if you follow the ILS glideslope to touchdown. There is a very slight downslope to the runway further confounding the stopping of a jet.

NTSB says plane landed at 4500' remaining which would be 427' past glideslope touchdown.

I indicated that a commercial pilot (cert) would have to demonstrate landing within 200' of a pre selected spot (at least I had to demo that to get my ticket).

BUT the NTSB has also said that you needed some 5300' to stop.

One question, does the handy dandy laptop computer with reversers figured it make its calculation from the THRESHOLD of the runway or from GS touchdown? I would bet "threshold" is the answer.

As someone indicated, it would be prudent in reduced visibility, night, snow and everything else to be right on the GS. As another pilot indicated, a ''non-flare'' landing to PLUNK it on at the GS intercept point of the runway would be prudent too.

AND to the great debate about "ducking" the Glideslope. And whether it is SOP or not. THE Federal Regulations are quite specific in that a Turbine powered plane must remain at or above the Glideslope. BUT IT ALSO SAYS THAT YOU CAN GO BELOW THE GLIDESLOPE WHEN REQURIED TO MAKE A SAFE LANDING. Generally this is regarded as the MM or equivelent position on the approach.

I recall an old joke at Midway. A jet was being towed off the runway after a virtual over run (not as deadly as the incident in question). The copilot said to the captain, "what happened?". The captain's reply was, "he followed the glideslope".

I have landed many times in 737's and DC9's (and once in a piper arrow!@) at Midway airport. EACH landing is a unique adventure and the criticality of the landing and approach (and indeed any operation there) must be studied.

Sometimes I would "duck" the glideslope in accordance with regulations, other times I would not. BUT each time I did, I had briefed this with the other pilot and verbally declared, "departing glideslope visually".

In retrospect this plane should not have landed on this runway in this wx.

IF reverse is to be credited towards landing distance (and I don't think it should be) then there must be an emergency memory item for "reversers fail to deploy".

1> are you above 100knots? if so, retract spoilers and firewall throttles FORWARD thrust and takeoff again.

2> are you below 100 knots, verify throttles idle, spoilers extended max toe braking and re attempt reverser deployment...if reversers deploy firewall REVERSE thrust to complete stop even if this damages the engines.

regards

jon

Clandestino

28th Jan 2006, 20:38

My local CAA allows thrust reverse to be used for ALD calculations on wet/contaminated runways but still LDA has to be 67% longer than ALD at destination or 42% at alternate. 560 or 30 ft on 4927ft long runway doesn't sound like 67% margin to me but then I'm no expert on FARs. Perhaps FAA allows lesser margins. Anyone on the other side of the pond care to comment?

Empty Cruise

28th Jan 2006, 20:55

Clandestio,

Can be overcome by dispatcing with a destination that is within the 1,67 planning margin when dry, but not when cont.

Now, due to the contamination, the runway is "below minima", and you dispatch with 2 alternates. Whopla, suddenly you're into "operational" requirements, not "planning" requirements.

Sad but true - and has happened!

Clandestino

28th Jan 2006, 22:02

Still don't get it but perhaps that is because our local interpretation is that prescribed margins must exist at touchdown i.e. they are operational and not dispatch margins. There is a bit silly situation when destination rwy has between 42 and 67 percent margin so it can be used as alternate but not as destination. To rectify it, 67% will be abolished soon.

punkalouver

28th Jan 2006, 22:17

they did not land 2000 feet down, they landed 1300 ft from the displaced threshold and 300 ft beyond the 1000 ft mark that the GS brings you to.
sounds like a spot on touchdown zone landing to me, some could argue you should duck under but that isn't SOP and the landing numbers are based on landing in the touchdown zone which they did.

Are you sure? I'm not sure. Looking at online approach plates, I got the airport chart for MDW which shows that there is a displaced threshhold of 696 feet. The airport chart shows a threshhold crossing height(TCH) of the 3.00° glideslope of 51 feet. Is this TCH for the beginning of the runway or is it for the displaced threshhold. I don't know. The approach plate doesn't say.
However, the 6869' long runway 01 at Washington National(chosen because of similar length) with no displaced threshhold has it's 3.00° glideslope TCH at 51 feet as well. Is an assumption being made on where the GPI(ground point of interception) is for the glideslope at MDW. Is it being assumed that it is 1000 feet beyond the displaced threshhold. The government approach chart doesn't say. Perhaps the Jeppesen chart does. It may very well be approximately 300 feet beyond the displaced threshhold.
If the DCA GS brings you to a 1000' touchdown point, I am assuming so does the MDW 31C GS does as well. If that TCH at MDW is over the very beginning of the runway, it would leave 5522' remaining instead of the "about 4500" feet of runway that the NTSB says actually did remain at touchdown. It would be nice to have this clarified.
However my original statement of landing 2000 feet down the runway would appear to be incorrect from a displaced threshhold point of view. It came from this Flight International quote "The Southwest Airlines Boeing 737-700 that overran Chicago Midway airport’s runway 31C onto a road landed about 620m (2,000ft) along the 1,990m snow-contaminated runway with a tailwind".

barit1

29th Jan 2006, 00:39

It might be good data to compile a list of which authorities permit the R/T stopping credit (under what circumstances, and when implemented), and which do not.

Inasmuch as reversers do not have the same degree of deployment redundancy as (e.g.) brakes, it seems a weak link in the system (as evidenced at KMDW)

bubbers44

29th Jan 2006, 14:21

Most of the time we operate out of 8,000+ runways so can be very conservative but if you always fly into Midway you have to rely on the charts to say yes or no.

My last seven years at AA I flew into Tegucigalpa, TGU, and a lot of times one degree or one knot of tailwind determined if the takeoff or landing was legal and if it was wet or dry. We couldn't put in an extra 500 feet for the kids. Why have charts approved by the FAA if you don't go by them. Either you are legal or you are not. Extreme circumstances like braking action poor to nil require judgement as to believing the charts but operating into marginal airports a standard method of operation is required. They were legal to land but I think the FAA will change the rules so thrust reverse won't be allowed to calculate landing distance like on all equipment I have ever flown.

Tanker

29th Jan 2006, 14:31

the NTSB has also said that you needed some 5300' to stop.
One question, does the handy dandy laptop computer with reversers figured it make its calculation from the THRESHOLD of the runway or from GS touchdown? I would bet "threshold" is the answer.
jon
The OPC makes it calculations from GS touchdown and not the threshold. You lose the bet.:)

jondc9

29th Jan 2006, 14:52

The OPC makes it calculations from GS touchdown and not the threshold. You lose the bet.:)

I am happy to lose this bet. It seems that you have special insight into this OPC system.

I will assume that you are a 737-700 pilot for this question then:

given a report of Fair braking action first 2/3 of runway and poor braking action the last 1/3 of runway would YOU enter ''wet poor'' or ''wet fair'' into your OPC?

who knows, you might even fly for SW. I don't want you to get in any trouble for answering the question.

AND if you did enter wet-poor and saw you would have a 30' margin, would YOU have made the approach?

punkalouver

29th Jan 2006, 16:26

The OPC makes it calculations from GS touchdown and not the threshold. You lose the bet.:)

Could you please tell us how far the GS touchdown point is from the end of the runway? Thanks.

AirRabbit

29th Jan 2006, 18:14

Good discussions, these. The thing that should be recognized is that there is a GPI and an RPI; Ground Point of Interception and Runway Point of Interception, and they are not necessarily the same. The GPI is where the glide slope intercepts the level plane of the runway threshold; and the RPI is where the glide slope intercepts the surface of the runway. If there is a slope on the runway, these points will differ, and they may differ quite a lot. It may seem like they shouldn’t be much different, but when you consider the shallow angle of the glide slope (3.00-degree, 2.88-degree, etc.) the difference can easily be in the hundreds of feet. And, as the glide slope shack is displaced off to the side of the runway, by varying distances, and the true glide slope (more of a parabola than a straight line) does not, or should not, intersect the runway (or even the plane of the threshold) the actual "glide slope intercept point" is always a good discussion issue.
_______
AirRabbit

jondc9

29th Jan 2006, 22:46

I actually think we have a good discussion going.

For the RECORD (please respond if incorrect)

CHICAGO MIDWAY runway 31Center usable length landing beyond GLIDESLOPE is:

4927feet.

landing beyond the displaced threshold of 31 Center is 5826 feet usable length.

899 feet between the displaced threshold and glideslope touchdown (theoretical touchdown if we want to be technical).

The runway itself is 6522 feet long ( like for takeoff man) 1595 feet that on an instrument approach could really not be used. (though read my discussion of ducking the gs above)

the NTSB says the plane landed with 4500 feet remaining. With my primative brain this means that the plane landed 427 feet beyond GS touchdown. 2022 feet of runway (concrete) that wasn't used due to legit reasons (displaced threshold.

I did make a comment that a commercial pilot has to demonstrate in his practical test landing within 200 feet of a spot. (of course this is done visually).

A casual glance would tell a novice pilot that the runway was 6522' long. But there are so many factors that really lead you to think you are lucky to have 4927' on a dark and stormy night with very low visability. would that 427 feet have been useful? I would say yes. Plane still might have gotten pranged up but not have gone onto roadway enough to hit car? But again, we still don't have all the facts.

I have a call into NTSB asking if spoilers deployed automatically. STILL no answer.

Remember folks this media (forum) does not do justice to any of our thoughts.

over

jon

punkalouver

30th Jan 2006, 00:16

"For the RECORD (please respond if incorrect)
CHICAGO MIDWAY runway 31Center usable length landing beyond GLIDESLOPE is:
4927feet."

Could you please tell me where you got this information from?

jondc9

30th Jan 2006, 01:00

"For the RECORD (please respond if incorrect)
CHICAGO MIDWAY runway 31Center usable length landing beyond GLIDESLOPE is:
4927feet."

Could you please tell me where you got this information from?

Do you know what a Jeppesen 10-9 page is? for those who don't, it is a very nice diagram of the airport in question along with (on the back) useable runway lengths including beyond gs.

So that's where I got the info. Anyone who has different info, please post. The runways haven't changed at MDW in a heck of a long time, but as my charts are slightly out of date (this century though!) someone might have newer info.

regards

jon

punkalouver

30th Jan 2006, 01:27

"Do you know what a Jeppesen 10-9 page is? for those who don't, it is a very nice diagram of the airport in question along with (on the back) useable runway lengths including beyond gs.
So that's where I got the info. Anyone who has different info, please post. The runways haven't changed at MDW in a heck of a long time, but as my charts are slightly out of date (this century though!) someone might have newer info."

Thanks. I don't have access to Jepp's for a few more days. This would seem to imply that the Threshhold crossing height of 51 feet for runway 31C is for the displaced threshhold. Possibly misleading to some pilot's using government charts if landing distance beyond the glidepath isn't mentioned somewhere else.

barit1

30th Jan 2006, 01:29

Count me, and my entire lunchbunch, in that 99.99%. I would REALLY like to known who/when/where the r/t credit originated. Was it -

Boeing?
A (potential) customer airline?
A Boeing competitor?
An external (foreign) jurisdiction?

Someone is responsible, right?

westhawk

30th Jan 2006, 05:02

Hi Punkalouver.

I was trying verify that figure as well. I have been off the last several days, so have not been around the Jepps to check this out. The only place I am accustomed to seeing distance remaining beyond glideslope is on the Jeppesen 10-9 pages along with the runway specifics. Now I see that Jondc9 has verified that as the source of his stated figure. (Easy, big Jon, I think Punkalouver just wanted to know the source of that info! Thanks for the verification.)

I do think that if they touched down some 400' beyond the rwy/ G/S intercept point, it is indicative of a minimal flare, sufficient only to reduce the impact with the runway to a moderate 5.0 on the Richter scale! Flying it into the ground with no flair might (at the ROD required to stay on glideslope at their groundspeed) likely have exceeded the certified structural limts of the airplane. (part 25 calls for 10 fps (600 fpm) at max ldg wt) And going below the G/S in minimum visibility conditions doesn't have much of a future in it either. So it seems entirely possible under the above assumptions that:

1) The approach was begun with the belief that it could be completed according to regulation and policy. I would also, giving this crew the benefit of any doubt, tend to think that they believed it could be safely accomplished. (albeit with no margin for error or failure)

2) The approach was flown accurately enough to put it down about where the most ideal profile that could be planned under the prevailing visibility conditions and allowing for a minimal sink rate reduction prior to touchdown would put it. Just for reference, 400' goes by in about two seconds at touchdown speed. Not much float there!

3) Had the reversers deployed when first commanded, a successful stop on the runway would likely have been completed. It is important to learn why they did not.

I'm not trying to say that any of this is proven fact. Indeed it it not yet that. Need more data (such as a CVR transcript and FDR traces) for that. But I do want to challenge this idea that this was a long landing or that they floated way down the runway just because there was 2000' of runway surface behind them at touchdown. Based upon what is apparent so far, this idea should at least be viewed with suspicion if it is not discarded alltogether.

Finally, This idea of allowing landings to be planned down to a gnat's behind, with no built-in safety margin, taking credit for the effect of reversers, to an icy runway in minimal IMC conditions, is at the least, deserving of a thorough audit. It must be determined if this procedure provides the desired level of safety margin appropriate for public transport aircraft service. Even if there is no intent to do so on the part of SWA or the FAA, allowing the procedure used to determine the required runway for this landing could have placed a subtle kind of pressure to "make it happen" on that crew. Most pilots are honest working folks who want to get it done if they can. Rules and company safety culture set the limits. Consideration must be given to the possibility that eliminating the "reverse credit" in the future may reduce the chances for a repeat occurance. In it's letter to crews regarding this issue, the SWAPA safety committee gave some very carefully worded, yet useful suggestions on dealing with the issue. Especially if you read between the lines a little. PICs are being called upon to earn their Captain's pay by using their command judgement to make the tough calls. The letter suggests some ways to justify it.

Best regards,

Westhawk

fepate

30th Jan 2006, 09:27

But I do want to challenge this idea that this was a long landing or that they floated way down the runway just because there was 2000' of runway surface behind them at touchdown. I must second this assertion. In the conditions that night, near minimums for the approach with a tailwind, the touchdown point seems entirely reasonable.

jondc9

30th Jan 2006, 15:58

barit1,

The SWAPA safety alert says reverse thrust credit is also used in RTO calculations.

This accident was a tragedy for the family of Joshua Woods (the 6 year old boy).

What concerns me even more is the aborted takeoff scenario at MDW (rto). Especially with the idea of TR's included in calculations. I grew up thinking that reverse was icing on the cake. Counting on reverse is something we shouldn't do!

But imagine taking off at max weight for runway 31center. AT V1 plus one knot BANG, massive engine vibrations, uncontained failure. The courage to FLY the plane shaking like hell will be the penultimate test of any pilot's mettle. To reject the takeoff at v1 or beyond will most certainly make the accident we have been discussing look like a picnic.

Legal and SAFE are spelled differently.

By the way, an engine failure departure procedure at MDW is no cinch, neither is the standard departure. Rapid turn within restricted airspace.

Be on your toes those who fly at MDW.

jon

Buster the Bear

30th Jan 2006, 22:02

So Joshua Woods, driving in his parents car, was killed by a rogue Boeing 737 landing at an airport. The on board Boeing computer calculated that an approach and landing could be easily conducted when the crew input the available data that they had access to.

As a mere by-stander, this is shocking! To potential Boeing passengers this must be awful, to read that on board computers, after years of use, are NOT fail safe?

Executive summary: the thrust reversers did not deploy properly, causing the plane to overshoot the end of the runway.

A point of contention right after the accident was that the pilots had apparently activated the automatic brake system in violation of Southwest policy, but the NTSB concluded the crucial factor was the unanticipated
18-second delay in the thrust-reversers deploying. As a result, NTSB is urging the FAA to to prohibit allowing for thrust-reversers in onboard stopping-distance calculations. (Before landing, the crew had used the onboard computer to calculate stopping distance for "wet-poor" conditions; those calculations assumed the thrust reversers would deploy normally.)

The risks here appear to be two of the most common ones: trusting an automatic system to activate within specification 100% of the time, and allowing that trusted system to be the critical margin between success and catastrophic failure -- even in the successful-landing scenario represented by the onboard computer's figures, the plane was anticipated to stop within
30 feet of the end of the runway after a rollout of over 4000 feet, a margin of error of less than 1%.

FACT or FICTION?

barit1

30th Jan 2006, 22:04

I went to www.faa.gov and did a Google of that site for "reverse thrust"- and found 259 hits.

But virtually all of them were related to Part 150 - Community Noise, placing restrictions on R/T to provide noise relief.

Is the airports side of the FAA talking to the aircraft side???:eek:

flown-it

31st Jan 2006, 00:07

This just in. 'bout time too!

National Transportation Safety Board
Washington, D.C. 20594
Safety Recommendation
Date: January 27, 2006
In reply refer to: A-06-16
Honorable Marion Blakey Administrator
Federal Aviation Administration
Washington, D.C. 20591

On December 8, 2005, about 1914 central standard time,
Southwest Airlines flight 1248, a Boeing 737-7H4,
N471WN, landed on runway 31C at Chicago Midway Airport
(MDW), Chicago, Illinois. The runway was contaminated
with snow. The airplane departed the end of the runway
and rolled through a blast fence and a perimeter fence
and then into traffic on an off-airport street. The
airplane came to a stop after impacting two cars,
which resulted in the death of a child passenger in
one of the vehicles. Of the 2 flight crewmembers, 3
flight attendants, and 98 passengers aboard the
airplane, 5 reported minor injuries, and the airplane
was substantially damaged. The flight was operating
under the provisions of 14 Code of Federal Regulations
Part 121 as a commercial passenger flight from
Baltimore/Washington International Thurgood Marshall
Airport, Baltimore, Maryland. Instrument
meteorological conditions prevailed for the flight.
The National Transportation Safety Board believes that
the urgent recommendation contained in this letter
requires immediate attention to restore landing safety
margins on contaminated runways.

Snow began to fall in the area surrounding MDW about 5
hours before the accident. While the flight was en
route and holding to land at MDW, the flight crew
obtained updated weather information and runway
braking action reports from air traffic control. On
the basis of this information, the flight crew planned
for fair braking action on landing on runway 31C. The
runway was last cleared and treated about 45 minutes
before the accident. About 30 minutes before the
accident, airport ground personnel performed a runway
friction measurement, which indicated that the runway
friction was â€œgood.â€ About 1/8 to 1/4 inch of
scattered snow was on the runway when the airplane
touched down.

Expected Landing Performance on Contaminated Runways

The flight crew used an on-board laptop performance
computer (OPC) provided in the cockpit of Southwest
Airlinesâ€™ airplanes to calculate expected landing
performance. For landing performance calculations,
flight crews enter flight specific data into the OPC,
including the expected landing runway, wind speed and
direction, airplane gross weight at touchdown, and the
reported runway braking action. The 737-700 OPC is
programmed to assume that the engine thrust reversers
will be deployed on touchdown1 and to calculate the
stopping margin (the runway distance remaining from
the front of the nose wheel to the end of the runway
pavement after the airplane comes to a stop). The OPC
then alerts flight crews if the remaining runway
distance is not sufficient for the airplane to land
and completely stop on the runway under the selected
weather and runway conditions.

The flight crew entered weather data into the OPC and
input WET-FAIR as the runway braking condition. The
OPC calculated that the airplane would be able to land
and completely stop on runway 31C under the selected
weather and runway conditions with about 560 feet of
runway remaining.2 During post accident interviews,
the flight crewmembers told Safety Board investigators
that they considered 560 feet to be an acceptable
safety margin and, therefore, decided to execute the
landing.

The assumption that engine thrust reversers would be
deployed on touchdown is consistent with Southwest
Airlinesâ€™ Flight Operations Manual, which states that,
when landing under less than good braking conditions,
the thrust reversers are to be used as soon as
possible during the landing roll and are to be applied
with the brakes. However, flight data recorder data
revealed that about 18 seconds passed from the time
the airplane touched down to the time the thrust
reversers were deployed; at that point, only about
1,000 feet of usable runway remained. During post
accident interviews, the captain stated that he
attempted to immediately deploy the thrust reversers
but that he was unable to do so. According to the
first officer, at some point during the rollout, he
noticed that the thrust reversers were not deployed,
and he then reached over and deployed them. The late
deployment of the thrust reversers almost completely
negated the stopping distance benefit that had been
expected because of the use of the thrust reversers.
The airplane departed the end of runway 31C at a
ground speed of about 50 knots.

Reverse Thrust Usage Credit

The Federal Aviation Administration (FAA) does not
allow the use of the reverse thrust credit when
determining dispatch landing distances. Further, the
decrease in stopping distance resulting from thrust
reverser use (which increases the safety margin) had
typically been used to offset other variables that
could significantly degrade stopping performance.

However, the FAA allows the reverse thrust credit to
be used in calculating en route operational landing
distances for some transport-category airplanes, such
as the accident airplane, a 737-700. Accordingly, when
using the reverse thrust credit for contaminated
runways, the required runway length for 737-700 model
airplanes is about 1,000 feet less than the required
runway length without the reverse thrust credit. The
OPCs of Southwest Airlinesâ€™ 737-300 and -500 model
airplanes do not use the reverse thrust credit;
therefore, these model airplanes have a greater
landing safety margin. In this accident, when the
thrust reversers were not (or could not be) used in a
timely manner, the airplane could not be stopped on
the runway because of the absence of this extra safety
margin.

1 Boeing 737-300 and -500 model airplanes are not
programmed with this assumption.
2 The flight crew also input WET-POOR as the runway
braking condition. The OPC calculated that a 30-foot
runway margin would remain.

If the reverse thrust credit had not been factored
into the stopping distance calculations made by the
OPC, it would have indicated that a safe landing on
runway 31C was not possible under a braking condition
of either fair or poor. The Safety Board is concerned
that the landing distance safety margin is
significantly reduced on a contaminated runway when
the reverse thrust credit is allowed in landing
stopping distance calculations. As a result, a single
event, the delayed deployment of the thrust reversers,
can lead to an unsafe condition, as it did in this
accident. The Safety Board concludes that the safety
margin must be restored to those airplanes for which
the reverse thrust credit is currently allowed in
landing performance calculations.

Therefore, the National Transportation Safety Board
recommends that the Federal Aviation Administration:
Immediately prohibit all 14 Code of Federal
Regulations Part 121 operators from using the reverse
thrust credit in landing performance calculations.

(A-06-16) Urgent

Acting Chairman ROSENKER and Members ENGLEMAN CONNERS,
HERSMAN,
and HIGGINS concurred with this recommendation.
By: Mark V. Rosenker
Acting Chairman
as70co/Midway/Midway Urgent Rec.doc
KSears drafted 1/9/06; revised 1/12/06;revised 1/20;
final 1/26/06

canyonblue737

31st Jan 2006, 00:18

One question, does the handy dandy laptop computer with reversers figured it make its calculation from the THRESHOLD of the runway or from GS touchdown? I would bet "threshold" is the answer.

Bzzz. Wrong answer. Calculations are made from GS touchdown aim point with further penalties for anticipated float due to flare dependent on if flying a flare visually or with HUD flare cue and set in the software by the pilot.

Also the 5300 stopping figure from the NTSB was based on not using TRs for 18 seconds as in accident case. Obviously TRs were predicted by the software and the pilots in their decision making to be deployed immediately so the predicted stopping figure would be well under 5300 ft, and under the 4900 or so feet available beyond the GS touchdown. Why the TRs were not able to be deployed is still being investigated obviously.

canyonblue737

31st Jan 2006, 00:21

I have a call into NTSB asking if spoilers deployed automatically. STILL no answer.

They absolutely did. Spoilers and Autobrakes both worked normally and immediately upon touchdown.

canyonblue737

31st Jan 2006, 00:22

Count me, and my entire lunchbunch, in that 99.99%. I would REALLY like to known who/when/where the r/t credit originated. Was it -
Boeing?
A (potential) customer airline?
A Boeing competitor?
An external (foreign) jurisdiction?
Someone is responsible, right?

The data is Boeing's, why they ran numbers that way is anyone's (good) guess.

Ignition Override

31st Jan 2006, 03:55

Pardon the editing/duplication errors. It is hard enough choosing the correct keys for the "control page" which should enable the Sturmovik combat game "Forgotten Battles" to extinguish a Bf-110 or P-38 "simulated" engine fire.:O

Ignition Override

31st Jan 2006, 05:28

Barit1: Check #333. Even if airports were to communicate openly with airline Flt. Ops Departments and Union Safety Officers, mistakes regarding runway treatment and/or braking action evaluations might still happen. Problems in controller 'shift change' created communication problems at DFW (microburst), Charlotte (different Approach frequencies during weather) and other places. Not to mention the problems verifying, between Tower Controllers and Ground Staff, what was done to the runways during winter weather with snow and ice on all surfaces.

It still interests me to find out whether the Southwest crew requested an ILS in the opposite direction, so that a headwind could have been possible.
Some advice to us has been to find out when the latest braking action report was made (was it a jet? or did the plane have props which can mostly use ground fine/reverse blade angles to slow down?), was the runway treated with chemicals, are the turnoff areas treated at all ;) , how much snow has fallen since the latest jet report?

A tailwind was never adviseable-even with just water on the runway. Next door to Midway, (ORD) O' Hare's runway 09R can feel like fair braking at best, with only light rain, and I made a PIREP to the Tower controller after we took the high speed (at a fairly low speed) exit. Even the big airports can have lots of rubber deposits- on the MIDDLE of the runways!

In the countries where most of you guys (and gals) live, airports operate by the book, therefore, these lessons are only for US pilots. Forget any "misson-oriented", "get-home-itis", desire to show the other (whether a guy or, especially a younger [female!]) pilot that you can handle anything. Don't land or takeoff if something does not seem quite right. Last leg of the trip-too da^^n$d bad. Who are they going to blame?

westhawk

31st Jan 2006, 06:29

It still interests me to find out whether the Southwest crew requested an ILS in the opposite direction, so that a headwind could have been possible.

Ignition Override:

If my memory serves me correctly, the reported visibility was less than the visibility minimums for the 13C approach, which were higher than the 31C approach. Subject to verification.

Best regards,

Westhawk

barit1

31st Jan 2006, 12:14

The data is Boeing's, why they ran numbers that way is anyone's (good) guess.

I'm sure the DATA comes from Boeing, and R/T accounting is fine for economics/statistical purposes - brake wear models, etc etc. It makes sense for the beancounter flying a desk.

My question is: Why did the FAA permit R/T accounting for flight planning? What made them change their minds? Who started down the slippery slope?
:ugh:

d246

31st Jan 2006, 13:25

Give it a rest boys, all this esoteric nonsense is all very well but, as those of us who operate commercial jets will tell you, putting one down on a runway of that length in those conditions is pushing one's luck to put it mildly.

jondc9

31st Jan 2006, 13:36

To CANYON BLUE:

You indicated that the auto spoilers deployed on landing and the auto brakes worked too.

How do you know?

The pilot reported no deceleration and started manual braking.

Were the throttles slightly forward of idle prohibiting deployment of thrust reversers?

Also, to all, the idea of using 13 Center has been brought up. some reported that the minimums were too high on that runway and the wx was not cooperating. I would just like to point out that one can hold for the wx to improve. One would have to wait awhile to get ORD to cooperate and the wx too. But still, it could have been done.

In fact, I have made the request going into midway. Initially I was told that I would have to hold for over half an hour. (this being an atc ploy I believe) As soon as I said I would hold for an hour if need be, amazingly I was vectored for the approach I wanted right away.

ALL pilots must remember that they (pilots) are the boss and the controllers are here to help the pilots, not the other way 'round.

jon

Tanker

31st Jan 2006, 15:17

I'm sure the DATA comes from Boeing, and R/T accounting is fine for economics/statistical purposes - brake wear models, etc etc. It makes sense for the beancounter flying a desk.
My question is: Why did the FAA permit R/T accounting for flight planning? What made them change their minds? Who started down the slippery slope?
:ugh:
For the same reason that a 2 engine jet is now capable of ETOPS certification, reliability. What seems like just a few year ago a 2 engine jet would never be certified for ETOPS. Now due to engine reliability they are. The same with the thrust reversers. Does better reliability means that safety is better. The aircraft manufacturers convinced the FAA that is the case.

canyonblue737

31st Jan 2006, 20:15

To CANYON BLUE:
You indicated that the auto spoilers deployed on landing and the auto brakes worked too.
How do you know?

intial NTSB press statements from FDR data revealed it. spoilers did deploy and autobrakes worked as designed. as for why the TRs didn't deploy i have no idea and no comment.

Tanker

31st Jan 2006, 21:39

2 engine jets still have one engine left if one fails. Using reverse thrust credit in this case is like flying over water in a single engine. If it fails you go down.
I'm not disagreeing with you. I was just pointing out that since engines are now more reliable that is why we have 2 engine ETOPs. Boeing must have used the same reliability logic to get the FAA to approve thrust reversers included in the landing data. IMO the logic is flawed, but is th only reason I and some of my co-workers can understand why it occurred.

jondc9

31st Jan 2006, 21:57

while the ntsb did say that autobrakes started to work and the PILOTS disengaged and went to manual braking I have seen NOTHING regarding the spoilers. If you have it, please post.

The captain has stated he went to manual braking because he didn't feel deceleration.

I spoke to the NTSB PR MAN and asked about the spoilers and they had no comment on that.

If I am wrong, please post NTSB DATA and I will appologize.

I will ask this question in the nicest way possible. Would southwest airlines have been the launch customer and / or made any purchase of the 737-700 series if reversers were not part of the stopping equation? That is, would a major redesign of the 737-700 have had to be made if it couldn't operate at MDW?

I once spoke to a guy hawking the BAE ATP (everyone remmber that plane?)

OUR little airline flew to TVL (south tahoe airport in california, KTVL for you across the pond). I asked if the BAE ATP could handle TVL on a hot day. the some 50-60 passenger plane could...but only with 2 passengers and NO luggage!!!!! The sales rep from BAE said, "well, you just won't go to TVL in this ".

Our airline didn't end up buying any BAE ATP's.

I wish I had the smoking gun on the -700...but until then I will just wonder...things that make you go, "hmmmmmm".

j

tribo

31st Jan 2006, 22:32

I guess this link would be of interest for this tread:
http://www.pprune.org/forums/showpost.php?p=2358633&postcount=43
Follow the links, open the document and make a search on any topic you want.
For this tread following keywords should be relevant: Southwest, Midway, thrust reverse, contaminated, +++++
You might learn something from the rulemaking process that could be useful

GregMagicQuist

1st Feb 2006, 06:59

All,

The 67% runway left discussions refer to PREFLIGHT, dispatch planning only. Upon arrival, you can "plan" to use ALL the runway if needed under the conditions, even if maximum stopping performance is required to have one foot left. (Not smart, perhaps, but legal). One "should" have some solid margin left upon arrival, though, BECAUSE OF that preflight planning requirement; which is the whole point of the preflight planning FAR with tons of "slop".

Approach end displaced threshold is NOT considered in landing distance math. TCH's are, therefore, AT the "threshold" where green lights and paint are. Displaced thresholds on the approach end are included for takeoff calculations only. Departure end displaced thresholds do "count" for landing and takeoff abort distances.

SWA OPC calculations assume ALL landings touch down 1500 feet from the "threshold" (not displaced threshold where takeoff roll starts). Following the HUD AIII mode WILL put you down 1500-2000 feet from "that" threshold unless "flare guidance" is ignored once visual. Hence, a 1000 foot additional margin is added to landing distance if "AIII" is selected for a real AIII low vis approaches with our 50 ft decision height. AIII published approaches only exist on long runways, so following flare cues in 700 ft RVR's is not a problem. It IS a problem at MDW. 31C ILS-Z is NOT an "AIII HUD" approach, but an "IMC HUD" approach (GS info goes away with no precision flare guidance at 35 ft). ILS-Z HUD only means IMC HUD (NOT "HUD AIII") and the new Jepps changes on the approach plate specifically disallow using the AIII approach. Heck, it is a CAT I approach requiring 3000 RVR! The special HUD use simply lowered the normal ILS DH from 250 ft AGL to 200 ft AGL in order to pick up the LDIN and threshold lites earlier.

It is EASY, and IMO, proper to "retarget" to the 500 ft point under such conditions using the HUD if one "had" to land at MDW for whatever reason (emergency, fire, etc). That gives one 1000 ft more stopping margin than OPC predicts!! Once visual at minimums, ease the HUD flight path marker (i.e. ground impact point!) onto the "real" threshold lites and drive in holding it there (on speed, of course) until the flare point at about 30 feet. If you do the trigonometry you get a 4.06 degree glideslope from 200 ft "on" the normal 3 degree glideslope (I.E. at normal DH) to the threshold (instead of to abeam the GS antenna at about 1000 ft from the threshold). There are no approach lites to "hit" anyway with the displaced thresholds. A 3 second or so flare "process" then makes you "miss" the threshold "impact point" and you safely touchdown around 500 ft down from it (with about a 20 ft TCH... no problem). IMO, this is perfectly safe, prudent, and legal by FAR's. It is “stabilized” also at just under 1000 fpm sink rate for average weights.

It is not SWA "SOP" to NEVER, EVER "duck under" or “retarget“ in any STRICTLY written verbiage (although it is in many pilot‘s minds). IMO, short, slick, runways make shortened “aim points” the SMART thing to do and there is wiggle room in "SOP" verbiage to do so (not to mention FAR's blatantly allowing it... see below). There is NOT an industry “land short problem”… there IS an industry “overrun” problem. If a 737 captain can't safely touchdown at the 500 foot point easily at any time you might need to -- IMO, that is problematic.

The regs allow a thinking pilot to do what is necessary after DH/MM glideslope-wise to ENSURE a safe landing. SWA removed (for unknown reasons... good, IMO) the short-lived 2004 revision language which stated we “fly the glideslope to the flare“ well before this accident. Here is the Reg:

FAR Part 91.129.e
“(2) A large or turbine-powered airplane approaching to land on a runway served by an instrument landing system (ILS), if the airplane is ILS equipped, shall fly that airplane at an altitude at or above the glide slope between the outer marker (or point of interception of glide slope, if compliance with the applicable distance from cloud criteria requires interception closer in) and the middle marker; and
(3) An airplane approaching to land on a runway served by a visual approach slope indicator shall maintain an altitude at or above the glide slope until a lower altitude is necessary for a safe landing.”

Respectfully,
GQ

jondc9

1st Feb 2006, 09:01

IF I were head of the FAA:

I would no longer allow "tail wind" operations at MDW. Its that simple. There are a few more airports in the country that would also take this hit, but its that simple.

Marginal airports for transport jets must have a number of safety factors :

All jets going into MDW would have to have operational thrust reversers if so equipped (the BAE 146 doesn't have thrust reverse but would be a great midway plane). Thrust reverse shall never be credited in landing distance.

MDW must have emas systems at the end of all runways used by transport jets.

MDW should have better approach lighting systems.

All "special" instrument approaches will hereby be cancelled.

MDW shall have better runway remaining alerting systems.

MDW airport shall have seperate and special alternate requirements and special holding fuel requirements. While alternate plus 45 minutes is OK for most airports, MDW shall have alternate plus 90.

j

jondc9

1st Feb 2006, 13:34

Mike

yes, caught between the devil and deep blue sea is right. But consider, pax want to go to Chicago, best damn alternate to MDW is ORD. BUT just try to get in line at ORD during a snow storm.

And to those who know Chicagoland, we must also wonder why the Mayor ordered bull dozers in to chop up and destroy MEIGS field and not Midway. If his logic had been used, Midway would be gone too. But $$$$ speaks louder than words.

Chicago is a great city. I love it! Its a todd'ln town. But if its going to have MIDWAY airport they should do it right and not half assed.

I recall how much they spent on the terminal to make it better, more modern and how little they did for the airport itself.

When I started flying to Midway in jets, the terminal looked just like it did in the movie "North by Northwest" (though with jetways).

j

tribo

2nd Feb 2006, 19:07

From - Southwest Airlines Runway Surface Condition Survey
November 1999 - May 2000 - I find that Southwest use the scale:

Dry
Wet-Good
Wet-Fair
Wet-Poor
0.25" clutter
0.50" clutter

The terms Wet-Fair and Wet-Poor where used the day of the accident.
In NTSB SIR-83-02 - Large Airplane Operations on Contaminated Runways, May 3-5, 1983, the 1980 edition of the Air Transport Association's Snow Removal Handbook describes Pilot terms for their members as follows:

GOOD - More braking is available than will be used in an average airline type deceleration. If a max energy stop were attempted, some distance in excess of certified stopping distance would be expected.
FAIR - Sufficient braking and cornering force is available for a well flown approach and landing using light braking. However, excess speed or long touchdown would result in an extremely low safety factor depending on runway length and crosswind component. Careful planning and good judgement are required.
POOR - Very careful planning, judgement and execution are absolutely essential. Crosswind becomes a "priority one" consideration. While a safe and successful approach, landing and stop can be accomplished if all factors are favorable, there is little room for error. Care must be exercised in every facet of the operation and a very careful evaluation of all existing conditions is necessary.
NIL - Extremely slippery with poor directional control even while taxiing. This is the kind of report we would envision during a freezing rain condition if nothing were done to the runways or taxiways.

Is there any description to the scale used by Southwest?
How does these scales relate to eachother?

tribo

3rd Feb 2006, 06:37

Thanks Bonger

Information from the NTSB letter to FAA dated January 27:
Snow began to fall in the area surrounding MDW about 5 hours before the accident. While the flight was en route and holding to land at MDW, the flight crew obtained updated weather information and runway braking action reports from air traffic control. On the basis of this information, the flight crew planned for fair braking action on landing on runway 31C. The runway was last cleared and treated about 45 minutes before the accident. About 30 minutes before the accident, airport ground personnel performed a runway friction measurement, which indicated that the runway friction was "good". About 1/8 to 1/4 inch of scattered snow was on the runway when the airplane touched down.
Under such circumstanses, would it not be more correct to use contaminated performance data THIN CLUTTER in stead of wet performance data WET-FAIR?

tribo

3rd Feb 2006, 11:34

Potuspilot

I was refering to the info in the NTSB letter - not what was actually passed on to the crew.
Thanks for the clarification of SCATTERED vs. THIN CLUTTER.
One could not read that from the scale as SCATTERED was not defined there.
Is there another scale including SCATTERED in existance?
Are there any guidance material related to the scale?

jondc9

3rd Feb 2006, 13:20

Perhap it is time to realize that all aviation enterprise must have safety backup in depth.

When a naval aviator attempts a landing on a carrier, he shoves throttle forward at touchdown just in case his hook misses the wire.

A backup plan must always exist. At MDW, there was no backup plan except perfection.

In depth safety:

1. EMAS overrun.

2. Emergency thrust reverser memory item checklist

3. higher approach minimums.

4. prohibition on tailwind operations.

5. Higher requirements for runway needed at MDW...instead of the 60percent rule, make it better at 50%.

While any airplane can over run any runway, MDW (lga, isp, sfo) all seem to need a bit more margin.

regards

jon

RatherBeFlying

3rd Feb 2006, 18:16

One press article mentioned that MDW had no room for EMAS and I can see that subtracting a few hundred feet from an already constrained runway has consequences on loadings and revenues.
So here's what to do: Convert the roads at the ends of 13-31C to underpasses
Put EMAS on top

barit1

3rd Feb 2006, 22:12

At the NW end, to gain more than a few hundred feet, you'd have to bury the rail lines too. Huge infrastructure cost.

How about some ATC refinements so that downwind landings aren't forced on the traveling public? Should be a whole lot cheaper & more efficient. :cool:

jondc9

4th Feb 2006, 00:09

<<<How about some ATC refinements so that downwind landings aren't forced on the traveling public?>>>

How about every pilot going to midway advises chicago center prior to handoff to approach control that they will not accept a downwind operation?

PILOTS its up to you, if you are still the commanders of your aircraft.

jon

tribo

6th Feb 2006, 07:44

Bonger
Thanks for the info with respect to the operational use of the THIN CLUTTER and 0.50 IN CLUTTER terms.
This info leads to the question:
How to make corrections for landing at a RWY contaminated with snow and ice (more than 25%)?
The description of the terms WET-GOOD, WET-FAIR and WET-POOR relates to wet runways.Note: “WET” runway conditions cover distances for braking actions only.

safetypee

6th Feb 2006, 16:19

tribo your question is at the centre of this accident and of many similar incidents.
There are industry wide problems with communication, assumption, and lack of knowledge.
Will the FAA’s failure to conform to ICAO Annex 14 be a contributory factor, or is it the general lack of standardisation for runway condition terminology involved? See Good - Fair - Poor – Nil (www.pprune.org/forums/showthread.php?t=201987) and Braking Action Table (www.pprune.org/forums/showthread.php?t=202109).
There appears to be a similar disparity in terminology between ATC, Operator, Dispatch, and Manufacturer (OPC), thus it should not be surprising that there are opportunities for error. In addition there are major issues relating to the accuracy of the runway friction measurement.
There appears to be a lack of knowledge as to what exactly is used to determine landing distance on contaminated runways and what safety margins exist or are required.
Historically the FAA has progressed from dry runways to factored wet, and now recommends an allowance for contaminated. JAA require measured or calculated contaminated data, but the safety margins may not be any better than for wet runways (JAR-OPS 1.520).
The Canadians have identified that a margin of 2.2 or 2.4 might be required to maintain an equivalent level of safety as opposed to the current 1.97 wet factor. Aircraft Braking Performance on Wet Concrete Runway Surfaces (www.tc.gc.ca/tdc/summary/14200/14273e.htm) and also see Benefit-Cost Analysis of Procedures for Accounting for Runway Friction on Landing (www.tc.gc.ca/tdc/summary/14000/14082e.htm). The latter PDF document includes the CRFI table and discusses risk and risk assessment (section 4), this is a ‘must read’ for all pilots.
Both the authorities and manufacturers place great responsibility on operators for interpreting the guidelines on landing distance.
Boeing (www.pilots.or.kr/upfile/aip/9AAAA_StoppingonSlipperyRwys2.ppt)
- If runway is reported to have slush/standing water covering, the flight crew should be suspicious of braking action reports and measured friction
- For landing, Boeing recommends the use of the data labeled ‘poor’ for slush/standing water due to the possibility of hydroplaning
- If runway conditions warrant, review the performance data to ensure the runway length exceeds the expected stopping distance by an adequate margin
There are also many human factors issues. The pilot is normally considered the last point of defense after all other defenses have failed, but for overruns there appears to be very few active defenses upstream of the pilot; it appears that the management of these or opportunity to implement them has already failed.
How to make corrections for landing at a RWY contaminated with snow and ice (more than 25%)?
For contamination with wet/slush/risk of aquaplaning, pilots should be balancing their choice of options on at least a safety factor of 2, i.e. double the sum of a ‘sporty’ 1000ft airborne distance from 50ft (landing at the correct speed), plus the published ground roll distance for the conditons. In addition there should be no tailwind or credit for reverse.

tribo

6th Feb 2006, 19:51

Safetypee et al
There are industry wide problems with communication, assumption, and lack of knowledge.There appears to be a similar disparity in terminology between ATC, Operator, Dispatch, and Manufacturer (OPC) the general lack of standardisation for runway condition terminology
I know the treads referred to (I started them) and I know the reports.
Please do not forget the ground staff who actually are the persons who identify the significant changes and report the conditions at the movement area.
I belive we all need to speak the same language and we should focus on that. There should be a standardised set of runway condition terminology across State borders used by:

Manufacturer - documentation
Authorities - sertification and operation
Airport operators - identifying significant changes and report them - (Main focus on getting rid of the snow and ice and then report)
Aircraft operators - SOPs

How can we achieve this?
ICAO is not "up to date" on the subject.
Who sets the agenda? (EASA? - GASR? http://www.airports.unina.it/home_eng.html)
(The Canadians and the Europeans (EASA) do make corrections for RWYs covered with more than 25% of snow and ice)

tribo

20th Jun 2006, 12:45

NTSB hearing at this link:
http://www.ntsb.gov/Events/hearing_sched.htm
FAA document at this link:
http://frwebgate.access.gpo.gov/cgi-bin/multidb.cgi?WAISdbName=2006_register+Federal+Register%2C+Vol ume+71+%282006%29&WAISqueryRule=%28%24WAISqueryString%29&WAISqueryString=landing+performance+assessments&WAIStemplate=multidb_results.html&Submit.=Submit&WrapperTemplate=fr_wrapper.html&WAISmaxHits=40

vapilot2004

20th Jun 2006, 22:36

Direct access links to CVR Transcript:
CVR (http://www.ntsb.gov/Events/2006/ChicagoIL%20SW/exhibits/349732.pdf)

Runway Friction Testing Log:

Link (http://www.ntsb.gov/Events/2006/ChicagoIL%20SW/exhibits/349245.pdf)

Aircraft Performance:
Link (http://www.ntsb.gov/Events/2006/ChicagoIL%20SW/exhibits/349734.pdf)

All released documents from NTSB on this:
Complete Exhibit List (http://www.ntsb.gov/Events/2006/ChicagoIL%20SW/exhibits/default.htm)

jondc9

20th Jun 2006, 23:53

Dear VApilot

Thank you for posting this information. I am on the mailing list for NTSB and still haven't gotten it that way.

My fellow aviators. I've read the CVR transcript. It is quite long, but every word gives insight.

(no jokes danny) I will refrain at this time from giving my views, as I would like to read this a number of times...I may even print it out and write notes on the side.

This is a rare opportunity to really get in the cockpit with this crew.

regards

jon

Ignition Override

22nd Jun 2006, 04:12

Jon DC-9: "Pilots it is up to you, if you are still commanders of your aircraft". Very good point.

One problem on various Pprune topics is that many of the "300-hour wonders" (or 500-) appear to be unsure, despite the fact that they are FOs (even as 'handling pilot') whether the pilot or the vnav/lnav/autothrottle is 'boss', or whether the automation is in command. The B-757 and the Airbus do require getting used to, but after that?

Part of the apparent confusion seems to be that their Flight Ops. policies seem to require the full use of all automation at almost all times, not just enroute but during takeoffs and approaches, as a substitute for lack of experience. With none or very little background flying planes such as the DHC-6 Twin Otter, Shorts 360, Emb-110 Bandeirante, Beech-1900 or SF-340 into major airports with a high traffic density (i.e. DFW or ORD), many airlines seem to be afraid of pilots experiencing what years ago, was quite normal.

Lufthansa has reportedly for many years had an excellent program at Goodyear, Arizona, where the ab initio student pilots even fly the high-performance Piper Cheyenne.
Jungs...AUSgezeichnet!

jondc9

22nd Jun 2006, 04:28

consider:

flying an automated plane, the pilot takes off, cleans up and engages the autopilot. what , about 3000 feet agl? climb to altitude, watching the autothrottles and the autopilot and yaw damper do their thing. We fly about 5 hours across the nation...descend on autopilot and click off, in trim, on glideslope and fly the last minute or so to touchdown (or an auto touchdown if you like).

ON a 5 hour flight, maybe, maybe 5 minutes of hand flying.

While I understand that southwest pilots hand fly a bit more, the whole idea is for the pilot to have a real feel for the plane.

to use the autobrakes, having NEVER trained on them, in a highly critical landing is akin to doing brain surgery without having held a scalpel before.

perhaps not, but somewhere the system failed. I understand the copilot is back to flying status, the captain is not, but is so close to the 60 retirement age, one can only imagine that he took his sick time and retired.

OPE

jon

FullWings

22nd Jun 2006, 08:33

I think that this sort of accident is fairly inevitable when many aeroplanes around the world are landing at restrictive airports in these kind of conditions.

There are too many variables involved in the actual line operation to be able to accurately predict stopping distances. You can work backwards from whatever happened to write the accident report and do it in great detail but it's very 'fuzzy' looking the other way.

There are many assumptions made when calculating landing performance but more importantly, the actual 'input' in the 'real world' is much more variable than, say, when taking off. If you had the same crew and aeroplane do a series of takeoffs and landings, using exactly the same technique each time, I would take a large wager that they would leave the ground in pretty much the same place each time but there would be far more 'scatter' in where they finally came to rest. I feel you would observe this effect on a dry runway in calm conditions, let alone in the middle of a snowstorm.

I think that it has become a matter of 'garbage in - garbage out' in some ways. If the wind and contamination state are not what you thought they were, you carry a few more knots over the threshold, float a bit, delay the reversers slightly, etc. these factors will soon erode all of your safety margin as they multiply up. If one of these things is causing the problem on it's own, it will be more obvious but a subtle combination of slightly exceeding a large amount of parameters will put you off the end just as surely.

My final point is that if you plotted calculated stopping distances against achieved stopping distances for a significant sample of flights, you would mostly likely end up with something approaching a 'normal distribution'. Once you have established that, it's only a matter of probability that someone will go off the end of a short, contaminated runway. It's the area under the tail of the curve, beyond the overrun point, that matters and that could be significant on the runway mentioned above.

I remember landing into ABZ (pretty comparable to Midway) one snowy night in a 737. We had done the calculations (using very conservative data), the runway friction had just been measured (we took a bit off to be on the safe side) and the wind was on the nose (we used nil). With full braking and max. reverse off a fairly firm touchdown, 'on the numbers', we eventually came to a halt 50m from the other end of the runway. Not an experience I wish to repeat.

captjns

22nd Jun 2006, 10:07

Boeing publishes, within the QRH advisory information for various regimes of flight.

As a rule of thumb, we use the “Normal Configuration Landing Distance” table, contained within our QRH, for the applicable landing flap setting to be used. The figures, corrections contained in the tables, such as weight, auto brake, wind, slope, etc. is then multiplied by two. The multiple is our reference for minimum desired runway length if the landing runway length is marginal. It is a very helpful tool.

Halfnut

27th Jun 2006, 23:22

http://www.aviationweek.com/avnow/news/channel_awst_story.jsp?id=news/aw062606p3.xml

FAA Policy Change Aimed at Ensuring Safe Landings

By: Frances Fiorino

06/25/2006 08:50:11 PM

MAKING LANDINGS SAFER

A proposed FAA policy revision--spurred by a fatal Southwest Airlines accident last winter--would require turbojet operators to establish methods of ensuring safer landings on contaminated runways.

On July 20, the FAA plans to issue a policy change dubbed "OpSpecs/MSpec Co82 Landing Performance Assessments." Under it, all turbojet operators are by Sept. 1 to submit to their principal operations inspectors proposed procedures that would assure a full-stop landing--with at least a 15% safety margin beyond the actual landing distance--could be made on the runway in the meteorological conditions at the time of arrival. Deceleration means and airplane configuration to be used must also be factored in. The procedures are to be in place by Oct. 1.

It means flight crews must make a specific calculation not before each landing, but only when they learn en route that conditions at a destination airport have deteriorated. In other words, the revised policy dictates that a pilot may not land an aircraft if a 15% safety margin is not available in the assessment, emergencies excepted, according to the FAA.

The policy affects all turbojet operators, Parts 91, 121, 125 and 135, who hold operations or management specifications or Part 125 letter of deviation authority. Foreign operators are excluded.

Southwest's runway overrun accident that spurred the changes occurred Dec. 8, 2005, at 7:14 p.m. CST. Flight 1248 was en route from Baltimore-Washington International to Chicago Midway, operating in instrument meteorological conditions. On landing on Midway's snow-covered Runway 31C, the Boeing 737-700 (N471WN) with 103 people on board, continued rolling through a jet blast deflector, an airport perimeter fence and onto a roadway.

It came to a stop there after hitting two cars and killing a six-year-old child in one of them. The accident injured another 12 people on the ground and four on board the aircraft.

The NTSB's June 20-21 hearing aimed at digging deeper for factual information about the accident--including runway friction measurement and methods used to relay those estimates to the flight crew, and aircraft landing performance on contaminated runways. Investigators continue to examine the braking system's effectiveness and the activation of thrust reversers.

The captain, who was flying the aircraft during landing, told the safety board the reversers were difficult to unstow. The flight data recorder readout indicates the first officer activated them, but not until 18 sec. after touchdown and 14 sec. before the collision with the jet blast deflector (AW&ST Dec. 19/26, 2005, p. 11). According to the NTSB documents, a pilot who flew the same aircraft prior to Flight 1248 said the brakes and reversers operated normally.

The cockpit voice recorder transcript indicates the tower advised the Flight 1248 crew Runway 31C conditions were "fair the first half," and "poor at the second half." By FAA definition, "fair/medium" conditions indicate "noticeably degraded braking conditions" and crews are to plan for long stopping distances. "Poor" indicates "very degraded" braking conditions with a potential for hydroplaning, and crews should plan for "significantly longer stopping distances."

The crew used an onboard laptop performance computer to calculate landing performance, based on factors such as wind speed and direction, aircraft gross weight at touchdown and reported braking action, according to the NTSB. The laptop, using "credit" for use of thrust reversers, calculated what remaining runway would be available after stopping under "wet-poor" and "wet-fair" conditions--and came up with 30-ft. and 560-ft. margins, respectively.

In January, the NTSB urged the FAA to prohibit airlines from using thrust reverser credit when determining stopping distances. If credit had not been included, the Flight 1248 laptop computer would have indicated a safe landing was not possible, according to the NTSB.

Following the accident, the FAA initiated an internal audit to assess the adequacy of current regulations and guidance information. The agency discovered about 50% of operators do not have policies in place to assess sufficient landing distances at time of arrival--even when runway conditions changed or had deteriorated from those forecast at departure. In addition, the FAA found that not all operators have procedures that account for runway surface conditions or reduced braking conditions. Thus the review led to the FAA's revised policy.

Meanwhile, the NTSB continues its probe, and acting Chairman Mark V. Rosenker says he hopes the final Flight 1248 report will be completed by year-end or early next year.

JustAnothrWindScreen

29th Jun 2006, 18:00

There are too many variables involved in the actual line operation to be able to accurately predict stopping distances.

I think that it has become a matter of 'garbage in - garbage out' in some ways.

Right on the mark FullWings. I don't think it has been said better. Now lets wait and see what the FAA in the USA comes up with. I do shudder at that thought.

flown-it

29th Jun 2006, 20:44

:ugh: Read the CVR transcript and weep. These guys had trouble working out a crossing restriction in the FMS, they struggled with the hold and they appear to be unsure of how to "clean up" the FMS for the final approach. Not to mention the question of the autobrakes and the unbelievable delay in activating reverse thrust.
Complex automated aeroplanes are here to stay. They will only get more automated. It's time to stop sticking our heads in the sand, wringing our wrists over how little stick time we get and acknowledge the real problem. We must understand the automation. We must train our crews to use that automation and we need to structure our sim instruction to that end. Endless V1 cuts, emergency descents and other time honoured checks make us great stick and rudder guys but don't prepare us for just such a scenario as this crew faced. They were a product of their training.
So read the CVR and weep..weep for this unfortunate crew who were given the tools but not the know how.

jondc9

29th Jun 2006, 22:34

flown it:

you make some excellent points. but there is one more point to be made...if they were excellent "stick and rudder" guys, they might have salvaged it...note:

"high on glideslope" call

no call outs of " spoilers deployed, reversers ready, no autobrakes, no calls of airspeed while decelerating (80 knots/60 knots)...

while southwest may have other callouts, I think something similiar to the above might be about right.

and TUNNEL vision...why didn't f/o scream, GET INTO REVERSE or something and not wait some 18 seconds. My gosh, that's the introduction and first strain of the "washington post march" in time!

and shame on southwest for putting a memo out about auto brakes and not training in the sim!

don't even get me started about tailwind landings at midway!

oh well

j

JustAnothrWindScreen

29th Jun 2006, 23:20

flown-it,

I agree with your assessment of learning the aircraft you are flying. That seems like a given and should not have to be explained. But at airports like MDW, no amount of automation or magic aircraft will help you if the conditions are against you and you decide to land. If you don't have "accurate information" to make an "informed decision", then accidents such as this will happen. The airport is safe but totally unforgiving when the conditions get tough. Operations will continue non stop out of MDW but this same accident or one very similiar will happen again as the airport has no room for error. There was a reason all the air carriers left MDW and moved to ORD many years ago. Just because we have LCC's trying to get an edge doesn't mean the airport is any different than it was 40 years ago.

jondc9

30th Jun 2006, 01:18

just another wind screen:

you are quite right. perhaps Chicago should have built ORD (orchard field) with the condition that MDW be non air carrier only. this could still be done by declaring the runways to be only 3800 feet long, with the rest as an over-run. not too many air carriers could make money at that field.

so too with the other metro area short fields that have been kept in use even thought JFK, IAD, DTW and the rest have been built.

j

barit1

30th Jun 2006, 11:36

... perhaps Chicago should have built ORD (orchard field) with the condition that MDW be non air carrier only...
j

With the beginnings of jet ops, MDW was phased out of sked ops in the early 60's. I rode a Lake Central DC-3 out of ORD in 1964 (with Stan Getz across the aisle); Before that, MDW was used by LCA, NCA, Ozark etc.

After deregulation, several carriers started moving back into MDW.

weasil

1st Jul 2006, 17:23

just another wind screen:
. this could still be done by declaring the runways to be only 3800 feet long, with the rest as an over-run. not too many air carriers could make money at that field.j

That would never happen while Richard Daley is in charge. He loves MDW, it makes money for the "outfit" that runs Chicago. And I personally love landing on that runway, you almost have to fly through the drive through to whitecastle as you cross the fence, but still, it's a hoot!

jondc9

1st Jul 2006, 19:49

weasil

I do agree with you that landing at MDW is a wonderful challenge to a pilot. One must be completely in the moment and one with the plane to plant it right where you want it and get the stopping drills underway.

But, how fun is the takeoff, and possible abort?!

j

West Coast

1st Jul 2006, 23:16

"perhaps Chicago should have built ORD (orchard field) with the condition that MDW be non air carrier only"

DFW had the Wright agreement to stifle competition. What would they call that one, the Daley agreement?

Ignition Override

5th Jul 2006, 00:44

A B-757 (300) ran off the end of what might have been a dry Midway runway, a few years ago. Because nobody was killed, thank God, I had almost no luck reading anything about the accident. A check of the NTSB website might help.

About five days ago during descent into Charlotte (CLT), near max landing weight (maybe 106,000#) for a 10,000' runway, 18R, I told the FO that if the tailwind component were to increase and go over 10 knots, we would immed. divert to GSP. No alternate fuel but had plenty of reserve + cont. This was a dry runway, but Charlotte Approach Control was not ready to "turn the airport around", as the wind direction was to improve. If the wind had increased, maybe ATC would have found the "commercial incentive" to allow planes to land on 36L and R.

Jon DC-9. Another top airport candidate on your list would also be DCA. Politics (world-class egos :cool: ) before safety. The FAA would never be allowed to consider closing it. Who appoints the top administrators? :hmm: Maybe "they" could allow some civilian charter flights into Andrews AFB, which has much longer runways. Security? A STAR into BWI takes you right over Andrews anyway-and BWI ops never required the ludicrous, former "daily secret code". Anybody could order Jepps. Maybe there is too much red tape for our enlightened bureaucratic "leadership" to sort out, as with the sad "Three Stooges Circus" after Hurricane Katrina. Too many bloated federal departments to "support"...

Never mind on many winter days at short runways such as Traverse City (TVC) MI. My company, due to incorrect airport runway treatments or past invalid braking action/RCR reports, has a detailed block of info in the Jepps for more than a few airports in the upper Midwest. Landing any jet, especially with no slats (CRJ), former DC-9 dash 10) into some of these places is seriously risking your career each time you go in, more so than with flaps and slatted wings.

Years ago, even at an airport (GFK) which has a very expensive, excellent university aviation school on location, some airport workers threw sand on an icy runway, but no chemicals, and a heavy jet slid off of the side, mostly due to the much reduced rudder ineffectiveness of tail-mounted engines. The Captain had never flown the plane as FO, for what it is worth-another trap.

Larry in TN

11th Jul 2006, 02:43

These guys had trouble working out a crossing restriction in the FMS

Southwest 737-700s have no VNAV nor autothrottles. About half of their fleet are 737-300s and 737-500s without the automation of the 737-700 so the guys get lots of hand flying. Low approaches are hand-flown by the Captain using the HUD. No autoland.

filejw

11th Jul 2006, 03:07

I believe you will find no 737-500's in the SWA fleet.

SeniorDispatcher

11th Jul 2006, 05:34

I believe you will find no 737-500's in the SWA fleet.

Actually, we have 25 of them, N501SW thru N528SW (skipping a few numbers)...

http://www.airliners.net/open.file/0917511/M/

3 in trail

11th Jul 2006, 05:42

Filejw

SWA fleet as of last week. 194 -300s, 25 -500s, and 243 -700s. 462 total

CaptainSandL

11th Jul 2006, 07:22

Does anybody know if the aircraft has been declared a write-off or will SWA be repairing it to save a hull-loss on their books?

SeniorDispatcher

11th Jul 2006, 08:31

As far as I know, N471WN will be repaired, but I don't if NTSB has released the aircraft yet so Boeing can commence the effort.

Shore Guy

11th Jul 2006, 13:07

An article in A.I.N. on the new FAA 15% rule states that the new computation would have only added 334 feet of required landing distance and asks the question “would that have made a difference” in the Southwest MDW accident.
http://www.ainonline.com/Issues/07_06/07_06_FAA_1.htm

flown-it

11th Jul 2006, 23:30

Larry in TN
Please read pages 66 and 66 of the CVR transcript.
Cross 30 South of Fort Wayne at FL 300 was the requirement. It appears to me they were trying to work out how to input that into the FMS in which case it's irelevant whether or not they had the ability to couple it to VNAV. They were using the FMS at the very least for SA.. and apparently having trouble doing that. THAT was my point.

Brian Abraham

25th Jul 2006, 04:50

FAA changes landing distance rules for commercial operators

By Matt Thurber “Aviation International News”, July 2006
After a Southwest Airlines Boeing 737-700 ran off a snowy runway while landing at Chicago Midway Airport on December 8 last year, the FAA launched an internal audit of factors related to that accident. One result of that audit is a new FAA policy that imposes mandatory 15-percent landing distance safety margins on Part 91K (fractional), 125, 121 and 135 jet operators. The rule was published in the Federal Register on June 7.

The new requirement is simple: no operator to which the policy applies is allowed to land on any runway without 15 percent more runway available than the actual landing distance. If weather conditions change en route, pilots will have to recalculate the actual landing distance needed, based on runway conditions and use of available equipment such as thrust reversers and spoilers, add 15 percent to that and determine if the destination runway is long enough. If not, they will have to find a suitable runway.

While the NTSB had not posted anything more than a brief preliminary report on the Southwest accident on its Web site, it did address the issue in a safety recommendation dated January 27. The flight crew’s calculation of runway needed to land, using the airline’s operational performance computer, showed that using the WET-FAIR runway braking condition parameter yielded a margin of 560 feet. In other words, if the condition of the runway actually matched the WET-FAIR parameter, then the pilots should have been able to come to a complete stop with 560 feet of runway remaining.
“During post-accident interviews,” the NTSB recommendation letter stated, “the flight crewmembers told Safety Board investigators that they considered 560 feet to be an acceptable safety margin and, therefore, decided to execute the landing.”

The NTSB didn’t take issue with the remaining runway length but criticized the FAA for allowing Southwest Airlines to consider thrust-reverser credit when determining landing distance in that model 737.
“The Safety Board is concerned that the landing distance safety margin is significantly reduced on a contaminated runway when the reverse thrust credit is allowed in landing stopping distance calculations. As a result, a single event, the delayed deployment of the thrust reversers [the NTSB said the flight crew waited 18 seconds after touchdown to deploy the reversers], can lead to an unsafe condition, as it did in this accident. The Safety Board concludes that the safety margin must be restored to those airplanes for which the reverse thrust credit is currently allowed in landing performance calculations.”

Most business jet operators don’t recognize thrust reverser credit when landing on contaminated runways, but the FAA’s new policy accepts that a variety of factors and equipment can be considered when calculating landing distance. Once that distance is calculated, the policy also requires adding the 15-percent safety margin, which probably would not have been obtainable in the Southwest Airlines case at Midway. (The runway used, 31C, is 6,522 feet long. Subtract 560 feet [the landing distance for the WET-FAIR wet-fair parameter] and that leaves 5,962 feet or a 9-percent margin. Add 15 percent–894 feet–and the total runway length with the new margin is 6,856. Would 334 extra feet have made a difference in this accident?)

The FAA requirements in the new policy are as follows: No later than Sept. 1, 2006, jet operators will be required to have procedures in place to ensure that a full-stop landing, with at least a 15-percent safety margin beyond the actual landing distance, can be made on the runway to be used, in the conditions existing at the time of arrival, and with the deceleration means and airplane configuration that will be used.

“This assessment must take into account the meteorological conditions affecting landing performance (airport pressure altitude, wind velocity, wind direction and so on), surface condition of the runway to be used for landing, the approach speed, airplane weight and configuration and planned use of airplane ground deceleration devices. Turbojet operators will be required to ensure that flight crews comply with the operator’s approved procedures. In other words, absent an emergency, after the flight crew makes this assessment using the air carrier’s FAA-approved procedures, if at least the 15-percent safety margin is not available, the pilot may not land the aircraft.”

The formal requirement for this new policy will come in OpSpec/MSpec C082, which will be available July 20. Operators must have procedures in place for complying with the new OpSpec/ MSpec by September 1, and the FAA expects all affected operators will be in compliance by October 1.

Both the National Air Transportation Association (NATA) and NBAA labeled the FAA’s release of the safety margin policy a quasi-rulemaking effort, noting that it was not subject to ordinary public comment and rule-drafting procedures.

“This proposal,” NBAA stated, “exceeds current regulations in place concerning landing procedures, and NBAA believes that, like all new proposals, this one should be subject to the time-tested federal rulemaking process for aviation regulations.”

NBAA also believes the policy is too narrowly focused. “By its nature, the proposal suggests that only one factor– runway landing distance–matters in aircraft landings. In fact, a whole host
of factors are involved, including pilot judgment, aircraft weight and other aspects of landing.” Although NBAA didn’t comment on the Southwest accident, some of the “host of factors” presumably could include proper use of thrust reversers and correct application of contaminated runway braking information, an issue the NTSB also raised.

“The FAA’s notice establishes a new regulatory requirement,” NATA explained, “bypassing the required rulemaking process, and is therefore unacceptable. The notice itself states that this is a new requirement, yet the FAA does not adequately explain why formal rulemaking was not conducted.”

NATA is more concerned about the FAA’s cavalier use of OpSpecs/MSpecs to impose new operational requirements. “The FAA attempts to sell this notice as ‘clarification’ of Parts 135.77, 125.351, 91.3 and 91.1009, which place responsibility for the safe operation of the flight jointly with the operator, pilot-in-command and dispatcher. The association submits that funneling new requirements through by claiming ‘clarification’ of these broadly worded regulations is an abusive interpretation of the regulations. The regulations cited by the FAA are general regulations intended to ensure that in all activities the aircraft is operated in a safe manner. They were not created to be used as an excuse for the FAA to impose specific requirements at any time, so that the agency can avoid the rigors of formal rulemaking.”

The FAR Part 91K and 135 regulation permitting operators of large transport-category airplanes to fly into airports where landing weight allows a full stop landing within 80 percent of available runway length shouldn’t be a factor in the safety-margin policy. If an airplane needs the full 80 percent of the available runway length, this still works out to be less than the amount required by the 15-percent margin policy.

For example, on Chicago Midway’s 6,522-foot-long Runway 31C, the 80-percent rule requires a full stop before reaching 5,217 feet. If 5,217 feet is the actual landing distance, adding 15 percent to that brings the required runway length to 6,000 feet, significantly less than the runway’s total length.

To view the new policy see
http://a257.g.akamaitech.net/7/257/2422/01jan20061800/edocket.access.gpo.gov/2006/06-5196.htm