Southwest B737 Overrun @ Chcago MDW
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I guess the "Stopping on Slippery Runways" info from Boeing on this link should be of interest:
http://rds.yahoo.com/_ylt=AnYEH_.rO9...pperyRwys2.ppt
http://rds.yahoo.com/_ylt=AnYEH_.rO9...pperyRwys2.ppt
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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.
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.
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The Airbus perspective on contaminated runways operations can be found at this link:
http://www.wingfiles.com/files/safet...operations.pdf
http://www.wingfiles.com/files/safet...operations.pdf
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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
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
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.
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.
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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.
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.
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.
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A Response to Mad (Flt) Scientist
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
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.
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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.
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.
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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 - -
- )
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.
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 - -
- )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.
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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.
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.
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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
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
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.
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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?
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?
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.
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.
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>>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?
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?
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>>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...
May I presume you don't fly large airplanes for a living? Like I said...
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Pilots,Physics, and AOC
... 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
KR
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"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.
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.
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What they call Immutable Logic Methinks
RatherbeFlying said
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.
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.
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.
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.
Join Date: Dec 2005
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ILS GLIDESOPE
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
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