SWA overrun NTSB preliminary facts.

[USMCmech]

Here ya go.

http://www.ntsb.gov/Pressrel/2005/051215.htm

Basicly they needed 5,300ft to stop and touched down with 4,500 to go.

For some reason the pilot couldn't get the TR levers to move right away.

31C was used even with a tailwind because it had lower mins for the aproach. The aproach for 13C would have been below mins.

 

[B767Driver]

Thrust reversers have no affect on FAA calculated landing distance. Their deployment or lack thereoff is not an input in stopping distance. They could have caused directional control problems, however.

 

[bob loblaw]

Are the thrust reversers activated by a squat switch which is activated by weight on the wheels? If so, the snow and aircraft speed could have been enough to keep the weight off the squat switch and rendered the reversers unusable until switch had enough weight on it to activate the thrust reversers. Just speculation though I do base this on an accident involving the Dallas Cowboy's LearJet which hit a dear on landing and damaged the squat switch which disabled the thrust reversers.

 

[AZBigDog]

Are the thrust reversers activated by a squat switch which is activated by weight on the wheels? If so, the snow and aircraft speed could have been enough to keep the weight off the squat switch and rendered the reversers unusable until switch had enough weight on it to activate the thrust reversers. Just speculation though I do base this on an accident involving the Dallas Cowboy's LearJet which hit a dear on landing and damaged the squat switch which disabled the thrust reversers.

There must be weight on the main landing gear wheels in order to deploy the thrust reversers on 737s. This also applies to the speed brakes.

AZ

 

[cime_sp]

For the CRJ you also need a certain number of the following (I think it's 3 but don't quote me...)

Weight on wheels
Wheel spin-up
Throttles @ idle
RA below a certain number of feet

...It's not uncommon to have diffuculty getting the TR's out. Sometimes it takes a few seconds. I also doubt that these pilots mashed the brakes. The approved stopping distances are for "maximum braking"...which basically means standing on them.

 

[Ophir]

which hit a dear on landing

Oh dear me!

I think you mean deer.


Hmm, this doesn't look good for the Capt.

"The flying pilot (Captain) stated that he could not get the reverse thrust levers out of the stowed position. The first officer, after several seconds, noticed that the thrust reversers were not deployed and activated the reversers without a problem."

You know what else seems fishy is that the stated length of the runway is "6522 x 150 ft.", subtract 500 ft to begin touchdown zone, and then have your legal 3000ft of precision landing distance and hmmm....

 

[Philip]

what does the area aside the runways look like there? Could he have put it off into the dirt in order to slow faster?

Either way, landing on a runway with what was it, 7" of snow? wasn't a good decision. The captain should take some heat for it.

 

[casey]

what does the area aside the runways look like there? Could he have put it off into the dirt in order to slow faster?

Either way, landing on a runway with what was it, 7" of snow? wasn't a good decision. The captain should take some heat for it.

http://maps.google.com/maps?q=mdw&ll=41.785521,-87.748446&spn=0.015048,0.048964&t=h&hl=en

'putting it in the dirt' would have involved making a turn on a surface that sounds like it didnt have a lot of traction. Once the nosewheel left the runway and into the snow you would probably have an airplane sliding sideways and when it impacted the perimiter wall the result could have been much worse.

Also, when you look at the image above, the maximum distance available to avoid a wall is down the runway, any deviation and you are decreasing distance to impact.

Where are you reading there was 7" of standing snow on the runway? My undestanding is that 31C and associated taxiways were plowed, with fair braking action at touchdown.

Personally, i'll wait for the NTSB final before making any judgement calls.

 

[Kingairer]

what does the area aside the runways look like there? Could he have put it off into the dirt in order to slow faster?

Either way, landing on a runway with what was it, 7" of snow? wasn't a good decision. The captain should take some heat for it.

7-12 inches is how much snow feel that nite. Not whats on the runway. Thats also like saying, why didnt he just stop on the runway and turn off on a taxiway.

 

[SteveC]

There must be weight on the main landing gear wheels in order to deploy the thrust reversers on 737s. This also applies to the speed brakes.

AZ

I have seen contrary reports on other web sites.

One indicated that " On the 737 the reversers will deploy when the air/ground safety sensor (squat switch) is in the Ground mode or either Radio Altimeter is less than 10 feet. A skip on the landing will not prevent reverser deployment. The pilot may choose to delay reverser deployment until on the ground to avoid a rapid return to earth."

Another said "The two squat switchers WERE on the PI 737-200s for a while but were removed after a loud response from the pilots about having to wait for the nose to be on to deploy the speedbrakes. Opening prematurely could cause the -200 buckets to scrape.

On the -300/400 one of the locks was the radio altimeter which would bias out below 50ft and you could open the reversers on the -300 in the air below 50ft AGL. Do not ask me how I know..."

I cannot verify, but believe both of these responses to be from current 737 pilots.

(edit to add: I do not know if this information applies to the model of 737 that was involved at MDW.)

 

[SteveC]

You know what else seems fishy is that the stated length of the runway is "6522 x 150 ft.", subtract 500 ft to begin touchdown zone, and then have your legal 3000ft of precision landing distance and hmmm....

That runway has a 696 foot displaced threshold as well. Available landing distance is 5,826 feet.

 

[Kingairer]

Add a tail wind, snow, etc etc and things start to add up.....or subtract.

 

[SteveC]

I still think that there is more to be learned before any conclusions can be reached.

If I understand what I have read (here and other locations), Southwest landing data is based on touchdown within 1500 feet of the beginning of the available runway. In this case, that would be with 5,826-1,500=4,326 feet left. According to the NTSB report, they touched down with 4,500 feet left, which should be within spec, assuming that their original calculations were correct.

It's interesting that the report mentions that the on-board computer, and the dispatcher, both agreed that the available landing distance was acceptable, yet the NTSB apparently calculated that 5,300 feet was needed for "stopping distance", and that "actual stopping distance was 5,000 feet". Pure conjecture here, but maybe the problem was in the tailwind component not being known, or factored in to the landing distance correctly? That additional 1,000 feet (mentioned in the report) would have made the difference.

Another interesting point that I haven't heard a definitive anwer for, is "does SWA's landing data include thrust reverse, or not". I believe that often the published data is based on braking only, no thrust reversers, but I don't know for sure. It might come into play in figuring out whether the problem with getting the reversers deployed in this case should have been, or was, the deciding factor.

Time will tell I guess.

 

[derg]

I'm not sure why the media (not the NTSB) is focusing on thrust reversers. As none of the calculated landing distances are based upon thrust reverser deployment. They really don't do much besides make a lot of noise on most aircraft.

 

[JaceTheAce]

Hmm, I'd rather not speculate and wait until the NTSB comes out with their report in a year (or less hopefully).

 

[AZBigDog]

I have seen contrary reports on other web sites.

One indicated that " On the 737 the reversers will deploy when the air/ground safety sensor (squat switch) is in the Ground mode or either Radio Altimeter is less than 10 feet. A skip on the landing will not prevent reverser deployment. The pilot may choose to delay reverser deployment until on the ground to avoid a rapid return to earth."

Another said "The two squat switchers WERE on the PI 737-200s for a while but were removed after a loud response from the pilots about having to wait for the nose to be on to deploy the speedbrakes. Opening prematurely could cause the -200 buckets to scrape.

On the -300/400 one of the locks was the radio altimeter which would bias out below 50ft and you could open the reversers on the -300 in the air below 50ft AGL. Do not ask me how I know..."

I cannot verify, but believe both of these responses to be from current 737 pilots.

(edit to add: I do not know if this information applies to the model of 737 that was involved at MDW.)

I haven't heard of the radio altimeter being involved in the deployment of TRs/speed breaks. Perhaps this is a modification on newer models of the 737. I'll have to read up on it.

 

[bob loblaw]

I'm not sure why the media (not the NTSB) is focusing on thrust reversers. As none of the calculated landing distances are based upon thrust reverser deployment. They really don't do much besides make a lot of noise on most aircraft.

My thinking about the thrust reversers question is if there wasn't enough weight on the wheels to deploy them, then there wasn't enough weight on the wheels for braking to have any effect due to the build up of snow on the runway. Kind of like hydroplaning except on snow. Also, If an airliner follows the glideslope all the way to touchdown, it should touchdown 1,000 feet down the runway. It sounds like the pilot was right on glideslope. I wonder who landed before the Southwest jet, and amount of time between their landing, and the Southwest landing.

 

[flyover]

On the -300/400 one of the locks was the radio altimeter which would bias out below 50ft and you could open the reversers on the -300 in the air below 50ft AGL. Do not ask me how I know..."

edit to add: I do not know if this information applies to the model of 737 that was involved at MDW.)

That was true of the -800 version. I would guess as well for these airplanes.

Thrust reverse is not required to calculae stop distances but we all know that in marginal braking the difference between being pushed down the runway by forward thrust (even at idle) and being able to use reverse thrust is a big factor.

Also, by electing to stand on the brakes they were probably getting less braking than they were on max auto-brakes, although with anti-skid cycling it may have been a tie. But in general if you can have the fortitude to let the auto-brakes do their "thang" it's supposed to be more effective.

 

[derg]

On the news here in PHX, they have a small newsticker that scrolls on the bottom of the screen. l think I've seen the most thought-inspiring, objective news nugget today:

"Airplane experts say that jet involved in deadly crash needed more runway to land"

Thank you channel 12... I'm sure your reporters were up late fact-checking THAT one. Bonuses all around.

 

[JaceTheAce]

On the news here in PHX, they have a small newsticker that scrolls on the bottom of the screen. l think I've seen the most thought-inspiring, objective news nugget today:

"Airplane experts say that jet involved in deadly crash needed more runway to land"

Thank you channel 12... I'm sure your reporters were up late fact-checking THAT one. Bonuses all around.

LOL! The classic "experts say" news media phrase.