737 runs off runway at Midway Chicago

[Brett327]

No reverse thrust, plus a snowy, short runway ... bad day for all.

FOX NEWS - Investigators: Reverse Thrusters Didn't Kick In Before Midway Accident

The plot thickens. Is that an area that is susceptible to ice build-up? Any airline guys have any amplifying info?

Brett

 

[A4sForever]

The plot thickens. Is that an area that is susceptible to ice build-up? Any airline guys have any amplifying info?

Brett

Reversers on the 737 (I'm typed) or any other turbojet transport that I am aware of are not "susceptible" to in flight ice build-up .... but in any case, reversers cannot be used for the calculated stopping distance on the runway --- so the AP/Fox News reverser report is of little import in the decision to shoot the approach and land.

That is, reversers are a bonus and while highly desirable, your calculations and those of dispatch have to assume they don't exist. The runway @ Midway was certainly "contaminated", i.e., anytime the runway has a visible "sheen" from precip in any form it is wet; contamination would include snow. This alone should have INCREASED the required stopping distance, if I am understanding what is going on here. And did they use auto brakes?? Don't hear any mention of it.

Again, short runways, bad WX, winds, contaminated runways, night operations, and the company breathing down your neck (perhaps not overtly -- but don't think it doesn't happen) .... leads to ..... what??? You gotta' use your judgment and your experience. It always cracks me up during a post-mortem when the FEDS, the airline, or the airport says anything like ... "conditions were acceptable" .... or other such tripe. That kind of bull-smoke is for the lawyers.

Remember, the FAA only requires a score of 70% on the test to pass --- that's "acceptable" to them --- we used to say the FAA standard was "70 and fly" for obvious reasons.

You, however, are required to be 100% in the cockpit. Nice, huh ???

 

[Brett327]

Good info, thanks good buddy.

Brett

 

[PropStop]

Hey A-4's, not being a jet guy I'm a bit confused about how the whole thrust reverser thing works (at least in terms of figuring your ground roll distance). How do you stop the plane if you're not using thrust reverse? Do you use the brakes at high speed or do you use aerodynamic braking?

I strive to make landings WITHOUT using brakes, at all. That’s also how I like to taxi. If I had a really short runway, of course I’d use brakes as needed, but if I don't have to, I don't.

How effective are thrust reversers compared to beta on a prop?

 

[HAL Pilot]

The plot thickens. Is that an area that is susceptible to ice build-up? Any airline guys have any amplifying info?

Brett

Not ice build up on the reversers, but maybe a failure of the air-ground switch (weight on wheels) on the main strut. If that switch failed in the air position (or was frozen during the approach?) the reverse thrust would have been rendered inop. No way for the pilots to know this until they try going into reverse.

I too am typed in the 737 but have never flown it (can you say Southwest?). In the DC-10, B-727 and Twin Otter if the reverse thrust is MELed (known inop) we take significant added runway length or max weight penalties. So while landing distance is calculated w/o reversers, we take an extra "hit" if they were known inop. We also plan on using the brakes from touch down vice doing a normal landing and plan on landing in the front portion of the touchdown zone. On a normal landing, we go into reverse on touchdown and slow to around 90 knots. By 80 knots we are out of reverse and now using brakes. If they did this, there might have been enough of a delay in their reaction time before braking to use up a lot of runway. Couple in the contaminated runway, the short runway, maybe having obscured runway markings and landing at the end of the touchdown zone, etc. I could see where this led to going off the end.

 

[mules83]

I had a friend who worked at flight safety in Wilmington and I got to ride in a G4 sim. The flight was practicing V1 cuts and they did it with and without thrust reversers. It was amazing to see how much thrust reversers affected your stopping distance.

 

[A4sForever]

.....How do you stop the plane if you're not using thrust reverse? Do you use the brakes at high speed or do you use aerodynamic braking?.......?

Brakes, BRAKES, BRAKES !!! And of course, idle power and speed brakes .... we don't aerodynamic brake the Whale --- although some idiots do in other airlines, usually foreign. It's too much metal to be screwing around with doing an aerodynamic "dance" down the runway after you touch down. Get down (weight on wheels) , slow down (idle, speed brakes, wheel brakes, reversers) and get stopped is always the name of the game. Jet transports are certificated for stopping/landing without reversers --- it makes sense as failures on touchdown are not uncommon. Auto brakes are very nice when it's not too hot outside. JAL uses them all the time and consequently they blow a lot of tires and melt a lot of heat plugs. "We" usually only use auto brakes with appropriate WX conditions and/or short runways.

I don't know about the A/G switch failing in "air" position ... although anythings possible. You'd think they would have gotten a horn if it failed in "flight/air" position when the gear/flaps were set for landing (?) Speculation: he also could have "greased it" on and/or landed long, thus delaying spoiler deployment and reverse thrust availability ---- increasing stopping distance when no more distance was actually available. Not kibitzing the accident, just trying to examine all possibilities.

As HAL and mules pointed out, you increase your stopping distance without reversers. But you can dispatch with a reverser INOP, based on the destination, predicted runways, and forecast WX. But you can't get a dispatch release with two reversers INOP .... guess the FEDs figure you ought to maintain your birds better than to launch with TWO inop???

I may move this thread to commercial aviation since that's what's going on ..... ??? My new policy is "No AW smiles ) ) for Christmas. A lump of coal for all those who like them ....

 

[HAL Pilot]

I don't know about the A/G switch failing in "air" position ... although anythings possible. You'd think they would have gotten a horn if it failed in "flight/air" position when the gear/flaps were set for landing (?)

On both the 727 and DC-10, initial indications of a failure of the A/G switch to go to "ground" are things like reversers failing to deploy and aircraft not fully depressurizing. There is no specific horn or warning light. It is a matter of things not working right and figuring out what they all have in common. It's been a while since my 737 systems classes, but I think it is basically the same.

On takeoff, failure of the A/G switch to go to "air" will give you such things as a T/O warning horn when you start retracting slats and flaps. The recent Greek 737 crash has been attributed to the pilots thinking the cabin altitude horn was a malfunction of the T/O warning horn (same horn used for both). While they were busy trying to figure out why they were having a T/O horn at altitude (and the A/G switch was discussed), everyone passed out from lack of oxygen. Got to love those foreign carriers and their training programs. A Captain and FO flying together, neither of whom had more then a very basic knowledge of ATC and checklist English and no common language.

But you can dispatch with a reverser INOP, based on the destination, predicted runways, and forecast WX. But you can't get a dispatch release with two reversers INOP .... guess the FEDs figure you ought to maintain your birds better than to launch with TWO inop???

This is why I think it might be something like the A/G switch failing. It has to go to "ground" for the reversers to deploy. The paper said there wer eno known mechanical descrepancies with the reversers/engines and for both to fail would be extremely strange. The A/G switch is the only thing I can think of that might cause this. Who knows - pure speculation.

 

[A4sForever]

.......It's been a while since my 737 systems classes, but I think it is basically the same......... I think it might be something like the A/G switch failing. It has to go to "ground" for the reversers to deploy. The paper said there wer eno known mechanical descrepancies with the reversers/engines and for both to fail would be extremely strange. The A/G switch is the only thing I can think of that might cause this. Who knows - pure speculation.

You have a point --- and it's been a while for me, too on the 737. It's possible. In any case, I think the most likely cause is just landing "long" .... i.e., just a little is too "long" at Midway --- short runways, bad WX, little/no braking, etc. ... in general a bad day.

Does anyone know what model 737 this was .... ???

 

[ChuckMK23]

You have a point --- and it's been a while for me, too on the 737. It's possible. In any case, I think the most likely cause is just landing "long" .... i.e., just a little is too "long" at Midway --- short runways, bad WX, little/no braking, etc. ... in general a bad day.

Does anyone know what model 737 this was .... ???

N471WN is the N Number in question

FAA shows it as a 737-700

http://registry.faa.gov/aircraftinquiry/NNumSQL.asp?NNumbertxt=471WN&cmndfind.x=19&cmndfind.y=18

737-700 stats:

http://www.airliners.net/info/stats.main?id=95

 

[selmacf7]

Anybody know how power settings are flown on that thing? EPR or N1 or something else? Just a thought, but the Air Florida Accident back in the 80's at DCA was caused by Icing of the Pt1 sensor (I think) in the fan cone. Pilots had false high on their EPR and never adjusted power... ended up on one of the bridges into DC.

That being a thought, probably not likely that a sensor would ice in flight... I've never heard of it. As for the 'reverse thrusters' being ised up, I would doubt it. Possible WOW switch was FUBAR, but I'm not sure how they work. I think he landed long with a slight tailwind (think his limit was 10kts) and it was just barely too much to get stopped. Sh*t happens, sucks that he killed a girl. Bunch of people will probably take a bunch of heat but I doubt much will change in terms of SW flying in and out of Midway.

 

[Gatordev]

I remember when that happened. I lived in Maryland at the time, and that was one nasty storm.

 

[A4sForever]

......think his limit was 10kts) and it was just barely too much to get stopped. ....

It is 10 knots .... in this case, my personal tailwind limit would be zero knots . Not second guessing the Captain --- that's what my limit would be under the circumstances in evidence and usually in MOST cases -- unless their was no other alternative. Obviously, I have not a clue if this was the situation here .... just talking generically.

I've gone against Dispatch more than once in my career when I thought they were making a bad call, and I'm still here to talk about it --- accident free. Cross fingers.

 

[codtanker]

SWA until yesterday also had a policy of not using Auto Brakes. This stems from the old days on the 737-200 they had that didn't have them. It was a standardization issue that they felt was bett not to use them company wide. I'm with A4's though, tailwind, poor weather and who knows what pireps the crew got just before landing on braking action.

I've had friends run the numbers for the -700 flying for other carriers and the numbers are very close to runway available. So close that there was no room for error, long landing or just poor braking.

 

[KBayDog]

I watched the show "Airline" last night, where the SW flight from Baltimore to Manchester, N.H. was diverted due to Wx at/below mins at Manchester. I found it amusing how the passengers were b!tching about it, and saying that the pilots could have landed in the weather, they have landed in worse, etc. etc. etc.

My question: Is it normal practice to take off at Baltimore, fly to Manchester, hold for a while, then divert all the way back to Baltimore (instead of landing somwhere closer to the destination)? Or does it have to do with Baltimore being a SW hub?