Southwest B737 Overrun @ Chcago MDW
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These data indicate that the accident airplane would have required about 5,000 feet of runway length after touchdown to stop using maximum autobrakes and about 4,700 feet of runway length after touchdown to stop using maximum manual brakes.
But what happens if there's some finger-trouble, or a moment's human hesitation on the flight deck?
I reckon I'd back the Autobrakes to stop me quicker than manual, more often than not. I'm sure the Boeing test pilot can glean a better result under test conditions. But these conditions were more test-ing, than test conditions, weren't they?
They must have invented the Autobrakes for a reason, and I'm sure it wasn't just to push up the price of an airframe.
VHCU
I believe that after Cranbrook, the reverser logic was altered to prevent in flight deployment. Reports that the crew had difficulty selecting reverse indicate that the reverser interlock logic may have got in their way.
As far as pedal vs. auto brakes are concerned, the end result is an integration over distance of:
brake pressure modulated by ABS
times
available friction.
Over the last few days I have had occasion to experience ABS in the car over a number of contaminated surfaces.
The absolute worst surfaces are those that have been partially treated in temperatures near the freezing point. The snow melts and then coaleases into what I can only characterise as grease over an ice layer. There ain't any braking action period on that stuff
It seems there were pilot reports of poor braking action at the departure end -- which does seem consistent with only some 90 kt of deceleration over some 5000 ft. I'm wondering if a V1 reject with partial reverse would have ended up in about the same place.
As far as pedal vs. auto brakes are concerned, the end result is an integration over distance of:
brake pressure modulated by ABS
times
available friction.
Over the last few days I have had occasion to experience ABS in the car over a number of contaminated surfaces.
The absolute worst surfaces are those that have been partially treated in temperatures near the freezing point. The snow melts and then coaleases into what I can only characterise as grease over an ice layer. There ain't any braking action period on that stuff
It seems there were pilot reports of poor braking action at the departure end -- which does seem consistent with only some 90 kt of deceleration over some 5000 ft. I'm wondering if a V1 reject with partial reverse would have ended up in about the same place.
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Sure, on the assumption everything went well and the manual braking was commenced at the optimal, i.e. earliest possible, time in the roll-out.
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Dec. 11, 2005, 3:56PM
Auto-braking shut off on Southwest jet that crashed
Associated Press
CHICAGO - The Southwest Airlines Co. jet that skidded off a snowy runway and into a Chicago street, killing a 6-year-old boy in a car, was equipped with automatic brakes, but the carrier's chief executive says the system was turned off so that the pilot could manually control the plane's landing. Chief Executive Gary Kelly also said the plane had been serviced the day before Thursday night's crash and showed no mechanical problems.
It was the first fatal crash in Southwest's 35-year history.
During a news conference at Southwest's Dallas headquarters before he left for Chicago, Kelly said it was too early to pinpoint the cause of the accident, which occurred during a snowstorm that reduced visibility at Midway Airport to between one-fourth and one-half mile.
Kelly said the role, if any, of the brakes won't be known until federal officials finish their investigation, which could take many months. The National Transportation Safety Board began its investigation within hours of the accident.
Kelly, however, defended the airline's policy of having pilots turn off the automatic braking system.
"We let our flight crews make the determination to brake the aircraft," he said. "It's just a choice, and we think that it's been obviously very, very successful over a long period of time."
Automatic brakes have been used on commercial airliners for many years, but they are not on all planes. For example, JetBlue Airways Corp. operates Airbus jets with auto-brakes and Embraer planes without them.
Jenny Dervin, a spokeswoman for JetBlue, said the airline requires pilots to use auto-braking under some low-visibility and bad-weather situations but declined to say whether that would have included Thursday night's conditions in Chicago.
At Delta Air Lines Inc., "They are on our fleets, and yes, they are used," said spokeswoman Gina Laughlin. She said pilots had some discretion in when to use the auto-brakes.
Officials at other carriers did not return calls or declined to comment on their policies.
On the Boeing 737-700, the automatic brakes are accompanied by an anti-skid system. They work like the antilock brakes on a car, using sensors to apply and release brakes quickly to prevent a skid.
Modern airliners are highly automated — on autopilot, they can take off, fly and land without human intervention — but pilots frequently override the automated systems.
Boeing does not tell airlines when pilots should use auto-brake systems, said spokeswoman Liz Verdier.
"There is not a right or a wrong way to do that," Verdier said. "They are used or not used in accordance with conditions or airline operational procedures." She said she saw nothing unusual in Kelly's statement that Southwest doesn't use automatic brakes.
At the federal safety board's request, Boeing on Friday sent an investigator and a systems engineer to help with the probe into the cause of Thursday night's accident.
The crash was reminiscent of a March 2000 accident in which a Southwest jet overran a runway at Burbank airport in Los Angeles, stopping just short of a gas station. The safety board said the accident was probably due to the crew landing the plane at too fast a speed.
In its final report on the Burbank accident, the safety board said the pilots probably could have kept the plane inside the airport fence had they applied maximum manual brakes immediately on touchdown.
The plane involved in Thursday night's accident was delivered to Southwest in July 2004. Southwest operates only Boeing 737s, and the 700 is the latest update to that model.
The plane had undergone a routine maintenance check Wednesday in Phoenix, Kelly said.
"There were no indications that the aircraft was experiencing any kind of maintenance problems," he said.
Southwest has no immediate plans to change operations at Midway, one of the carrier's largest operations with 196 daily departures. Southwest had operated there for 20 years without a previous incident, said Kelly, who termed the 6,500-foot runway adequate.
Still, the accident raised questions about Southwest's operations at smaller airports, some of which, like Midway, are surrounding by houses and commercial buildings.
Some Dallas residents have raised safety arguments against Southwest's plans to expand long-haul flights from Love Field. Kelly said Thursday's accident should have no bearing on the debate in Congress over expanding Love Field, which has an 8,800-foot runway.
"They are obviously different airports with different runways and different configurations," he said.
Auto-braking shut off on Southwest jet that crashed
Associated Press
CHICAGO - The Southwest Airlines Co. jet that skidded off a snowy runway and into a Chicago street, killing a 6-year-old boy in a car, was equipped with automatic brakes, but the carrier's chief executive says the system was turned off so that the pilot could manually control the plane's landing. Chief Executive Gary Kelly also said the plane had been serviced the day before Thursday night's crash and showed no mechanical problems.
It was the first fatal crash in Southwest's 35-year history.
During a news conference at Southwest's Dallas headquarters before he left for Chicago, Kelly said it was too early to pinpoint the cause of the accident, which occurred during a snowstorm that reduced visibility at Midway Airport to between one-fourth and one-half mile.
Kelly said the role, if any, of the brakes won't be known until federal officials finish their investigation, which could take many months. The National Transportation Safety Board began its investigation within hours of the accident.
Kelly, however, defended the airline's policy of having pilots turn off the automatic braking system.
"We let our flight crews make the determination to brake the aircraft," he said. "It's just a choice, and we think that it's been obviously very, very successful over a long period of time."
Automatic brakes have been used on commercial airliners for many years, but they are not on all planes. For example, JetBlue Airways Corp. operates Airbus jets with auto-brakes and Embraer planes without them.
Jenny Dervin, a spokeswoman for JetBlue, said the airline requires pilots to use auto-braking under some low-visibility and bad-weather situations but declined to say whether that would have included Thursday night's conditions in Chicago.
At Delta Air Lines Inc., "They are on our fleets, and yes, they are used," said spokeswoman Gina Laughlin. She said pilots had some discretion in when to use the auto-brakes.
Officials at other carriers did not return calls or declined to comment on their policies.
On the Boeing 737-700, the automatic brakes are accompanied by an anti-skid system. They work like the antilock brakes on a car, using sensors to apply and release brakes quickly to prevent a skid.
Modern airliners are highly automated — on autopilot, they can take off, fly and land without human intervention — but pilots frequently override the automated systems.
Boeing does not tell airlines when pilots should use auto-brake systems, said spokeswoman Liz Verdier.
"There is not a right or a wrong way to do that," Verdier said. "They are used or not used in accordance with conditions or airline operational procedures." She said she saw nothing unusual in Kelly's statement that Southwest doesn't use automatic brakes.
At the federal safety board's request, Boeing on Friday sent an investigator and a systems engineer to help with the probe into the cause of Thursday night's accident.
The crash was reminiscent of a March 2000 accident in which a Southwest jet overran a runway at Burbank airport in Los Angeles, stopping just short of a gas station. The safety board said the accident was probably due to the crew landing the plane at too fast a speed.
In its final report on the Burbank accident, the safety board said the pilots probably could have kept the plane inside the airport fence had they applied maximum manual brakes immediately on touchdown.
The plane involved in Thursday night's accident was delivered to Southwest in July 2004. Southwest operates only Boeing 737s, and the 700 is the latest update to that model.
The plane had undergone a routine maintenance check Wednesday in Phoenix, Kelly said.
"There were no indications that the aircraft was experiencing any kind of maintenance problems," he said.
Southwest has no immediate plans to change operations at Midway, one of the carrier's largest operations with 196 daily departures. Southwest had operated there for 20 years without a previous incident, said Kelly, who termed the 6,500-foot runway adequate.
Still, the accident raised questions about Southwest's operations at smaller airports, some of which, like Midway, are surrounding by houses and commercial buildings.
Some Dallas residents have raised safety arguments against Southwest's plans to expand long-haul flights from Love Field. Kelly said Thursday's accident should have no bearing on the debate in Congress over expanding Love Field, which has an 8,800-foot runway.
"They are obviously different airports with different runways and different configurations," he said.
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On the Boeing 737-700, the automatic brakes are accompanied by an anti-skid system. They work like the antilock brakes on a car, using sensors to apply and release brakes quickly to prevent a skid.
As pointed out by Willie Everlearn
applying manual braking can and does result in one unconsiously varying the pressure to the pedals. This trait is magnified in a crosswind where one is at times walking the rudder more than normal to maintain directional control. I always use 'em and in 16 plus years they've never let me down.
Oh and did anyone see the SLF interviewed the next day who in addition to the usual "terrifying ordeal " stuff so beloved by CNN said that "We could feel the pilot pumping the brakes" Duh!! Bet he will be the first to sue his car company when he pumps his ABS equiped brakes in a skid!!
studies would suggest and validate the ABS to be far more efficient and effective than manual braking. By this I mean the ABS applies a more constant [pressure] than the human. We tend to adjust or vary pressure over the nano seconds, as we gain a feel for the pedals and braking. (That's what the scientists suggest, not me, I just think it stands to reason so I've accepted their suggestion on this). So it would seem to me an interpretation as to when and how we apply brakes under varying conditions which could prove disasterous. Timing must be everything, eh?
Oh and did anyone see the SLF interviewed the next day who in addition to the usual "terrifying ordeal " stuff so beloved by CNN said that "We could feel the pilot pumping the brakes" Duh!! Bet he will be the first to sue his car company when he pumps his ABS equiped brakes in a skid!!
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Clampers
The anti-skid does work with manual braking to aid the pilot in directional control and reduce stopping distances on wet or slippery runways. For manual braking pilots are taught to apply constant brake pressure and allow the antiskid to do its' job when runways are slick or when stopping distance is critical.
The anti-skid does work with manual braking to aid the pilot in directional control and reduce stopping distances on wet or slippery runways. For manual braking pilots are taught to apply constant brake pressure and allow the antiskid to do its' job when runways are slick or when stopping distance is critical.
Just a numbered other
One thing I've noticed flying the 737 is that the shorter the runway/worse the conditions, the quicker pilots want to get reversers deployed, with the inevitable result that their first attempt at reverse is baulked by the interlock.
Frantic battles ensue which, had a moment's hesitation been employed after touchdown, would not be needed.
Try this whilst trying to remember to apply full manual brakes, and it is unlikely that your stopping distance will be the shortest possible.
These observations are in no way a comment on this accident.
My thoughts are with the family of that poor child.
Frantic battles ensue which, had a moment's hesitation been employed after touchdown, would not be needed.
Try this whilst trying to remember to apply full manual brakes, and it is unlikely that your stopping distance will be the shortest possible.
These observations are in no way a comment on this accident.
My thoughts are with the family of that poor child.
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I am intrigued as to why an approach was made.
Braking action medium, 55,000 kg, Flap 40, 8 knot tail, Vref40+5:
AB3 = 7125'
ABMAX = 6975'
If braking action poor, then it's 9214' with ABMAX. Add 1265' if you only have one reverser, add 3335' for no reversers.
All these include 1150' of air distance, so should be compared with the 6500' of available runway. Sure, they include a 15% factor, but I (unless in an emergency) would like a touch more than 15%. So why was an approach made?
Even if they did a perfect "testpilot" (no flare) landing, it would overrun.
If they decided to go for max manual braking (totally mad on a contaminated runway - how do you slam on the brakes on touchdown AND steer at the same time?) then the figure is 6735' (8909' if braking action poor). Still too far.
A common error in the -700 when landing Flap 40 is a slightly extended flare (due to the unusual attitude). This was a particular problem when light (as they were). The grappling with the reversers problem only ever ocurred for me on the -300 (I suspect because of the 10' RA on the -700).
The -700 lands well on short runways. It also lands well (when using AB) on contaminated runways.
But I wouldn't like to try and combine the two.
Braking action medium, 55,000 kg, Flap 40, 8 knot tail, Vref40+5:
AB3 = 7125'
ABMAX = 6975'
If braking action poor, then it's 9214' with ABMAX. Add 1265' if you only have one reverser, add 3335' for no reversers.
All these include 1150' of air distance, so should be compared with the 6500' of available runway. Sure, they include a 15% factor, but I (unless in an emergency) would like a touch more than 15%. So why was an approach made?
Even if they did a perfect "testpilot" (no flare) landing, it would overrun.
If they decided to go for max manual braking (totally mad on a contaminated runway - how do you slam on the brakes on touchdown AND steer at the same time?) then the figure is 6735' (8909' if braking action poor). Still too far.
A common error in the -700 when landing Flap 40 is a slightly extended flare (due to the unusual attitude). This was a particular problem when light (as they were). The grappling with the reversers problem only ever ocurred for me on the -300 (I suspect because of the 10' RA on the -700).
The -700 lands well on short runways. It also lands well (when using AB) on contaminated runways.
But I wouldn't like to try and combine the two.
Last edited by Stu Bigzorst; 13th Dec 2005 at 19:16.
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Manual braking?
I never tried manual braking on an airplane. It seems to work okay on my motorcycle, on the front brake at least, but I find pedal braking works much better on an airplane. There are issues of access to the brake controls and maintaining visibility during roll-out that must be addressed when using manual braking that would seem to preclude the practice.
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Did the crew know of the 90 deg 10 knots wind the NTSB gave us in the press conference? Or did they get an older value like the 23003KT from the 0153z METAR?
KMDW 090053Z 10011KT 1/2SM SN FZFG BKN004 OVC014 M03/M05 A3006 RMK AO2 SLP196 R31C/4500FT SNINCR 1/10 P0000 T10331050
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>>...R31C/4500FT SNINCR 1/10 P0000 T10331050
I don't have my Microsoft Flight Simulator decoder ring handy. What does this secret stuff mean?
Hopefully nothing significant.
How many crashes do we need to get human readable notams and weather?
I don't have my Microsoft Flight Simulator decoder ring handy. What does this secret stuff mean?
Hopefully nothing significant.
How many crashes do we need to get human readable notams and weather?
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I believe that indicates an RVR of 4500' on rwy 31C. I wouldn't hazard a guess on the rest without a cheat sheet. If so, it confirms the other runways weren't available because the vis was below mins for them.
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The aircraft landing just prior reported "fair to poor" braking action.
In the meantime, heavy snow was falling. Braking isn't going to magically get any better since the report, more likely worse. We're paid to know this, and factor possible deterioration it into our decisions.
Midway (been there many times, summer and winter) = short runways = not a lot of margin for error even on good days.
Contaminated runway
Known tailwind
Autobrake vs. manual max braking.....semantics. The aircraft hit the fence past the end of the runway at 40kts.....in other words, it wasn't even close.
Every landing (or T/O) involves the use of numbers, but some numbers are really variables (tw higher than reported, that braking action reports involve some degree of subjectivity and/or coefficient instrumentation doesn't cover every inch of where your wheels will be). Remembering this fact....where the numbers come from and their inherent limitations with regards to accuracy....should be of prime concern when making decisions that allow NO room for error.
Maximum-effort landings are a rare thing in airline ops...the REQUIREMENT to make one due to tight book numbers even rarer. When faced with "assuming the best" in order to make the book numbers work, that's the time to get your head out of the book and recognize that your assumptions could easily be at odds with the reality, and how does it fit in with managing risk?
Assuming the best at Dulles or O'hare etc. and being wrong means you miss a turn-off and continue to the next one. Doing the same things at Midway is entirely different.
In the meantime, heavy snow was falling. Braking isn't going to magically get any better since the report, more likely worse. We're paid to know this, and factor possible deterioration it into our decisions.
Midway (been there many times, summer and winter) = short runways = not a lot of margin for error even on good days.
Contaminated runway
Known tailwind
Autobrake vs. manual max braking.....semantics. The aircraft hit the fence past the end of the runway at 40kts.....in other words, it wasn't even close.
Every landing (or T/O) involves the use of numbers, but some numbers are really variables (tw higher than reported, that braking action reports involve some degree of subjectivity and/or coefficient instrumentation doesn't cover every inch of where your wheels will be). Remembering this fact....where the numbers come from and their inherent limitations with regards to accuracy....should be of prime concern when making decisions that allow NO room for error.
Maximum-effort landings are a rare thing in airline ops...the REQUIREMENT to make one due to tight book numbers even rarer. When faced with "assuming the best" in order to make the book numbers work, that's the time to get your head out of the book and recognize that your assumptions could easily be at odds with the reality, and how does it fit in with managing risk?
Assuming the best at Dulles or O'hare etc. and being wrong means you miss a turn-off and continue to the next one. Doing the same things at Midway is entirely different.
Last edited by AMF; 14th Dec 2005 at 10:35.
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R31C/4500FT SNINCR 1/10 P0000 T10331050
I don't have my Microsoft Flight Simulator decoder ring handy. What does this secret stuff mean?
I don't have my Microsoft Flight Simulator decoder ring handy. What does this secret stuff mean?