Southwest B737 Overrun @ Chcago MDW

[tribo]

Re: Southwest B737 Overrun @ Chcago MDW

An "old" update at this link:

http://abcnews.go.com/Business/Flyin...ory?id=1412384

[handflying]

Re: Southwest B737 Overrun @ Chcago MDW

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]

Re: Southwest B737 Overrun @ Chcago MDW

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]

Re: Southwest B737 Overrun @ Chcago MDW

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]

Re: Southwest B737 Overrun @ Chcago MDW

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]

Re: Southwest B737 Overrun @ Chcago MDW

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]

Re: Southwest B737 Overrun @ Chcago MDW

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]

Re: Southwest B737 Overrun @ Chcago MDW

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]

Re: Southwest B737 Overrun @ Chcago MDW

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]

From USA Today:
http://www.usatoday.com/news/nation/...warnings_x.htm
http://www.usatoday.com/news/nation/...ay-skids_x.htm

[d192049d]

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]

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]

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]

Forum readers and others may benefit as well

- well, I certainly will. Thanks to the team for some useful insights.

[tribo]

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]

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]

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]

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?

[jondc9]

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

[Tanker]

Originally Posted by jondc9

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.