OT - Southwest crash

[Guest D17S]

Interesting. So if the airplane touched down with 4500 ft remaining and it would have needed 5300 to stop even if everything had worked right, the rest is just about how many streets into the adjoining neighborhood did the airplane finally come to rest. While autobrakes were still the right choice, but it appears that ABs, TRs, a drogue chute even an anchor thrown out the window wouldn't have saved this landing. I guess I could plug it into my FMC right quick, but how long was that runway? Some of our real pilots might do a runway analysis to see how those numbers work out. The story will be there. As far as the ABs though, we have discussed that the system needs 'on the ground' (squat / tilt / etc) and wheel spinup. When it engages, the AB system will provide pressure to the antiskid control valves, but still no brakes will be applied until the antiskid system is happy. The AS system will look for an array of logic to allow any brake to engage. Both the AB system and the manual peddle action provide pressure to these same AS valves. The point is that during that initial brake engagement sequence, the pilot cannot get brake pressure to the wheels quicker than the AB system. The best he can hope for is a tie. With that argument considered, the discussion might continue:

[Guest tmetzinger]

> Interesting. So if the airplane touched down with 4500 ft>remaining and it would have needed 5300 to stop even if>everything had worked right, the rest is just about how many>streets into the adjoining neighborhood did the airplane>finally come to rest. While autobrakes were still the right>choice, but it appears that ABs, TRs, a drogue chute even an>anchor thrown out the window wouldn't have saved this landing.>I guess I could plug it into my FMC right quick, but how long>was that runway? Some of our real pilots might do a runway>analysis to see how those numbers work out. The story will be>there. >NO NO NO. The amount of braking/reverse thrust ACTUALLY used (with the reversers late) needed 5300 feet, not the amount of braking/reverse thrust available. (and they used 5000 of that, the distance was shortened by the impact with the fence, etc).If the reversers were activated sooner that the distance would have been decreased, but I can't say for sure whether it would have been decreased to less than 4500. I bet it would have.Looking at the chart I see that landing distance is 4900 feet past glideslope - so the pilot landed within the first 400 feet of his "available" runway. Again, nothing in the NTSB report indicates that the pilot was fast, high, or anything else. The only issue was that the pilot claims he couldn't get the reversers activated. The FO was able to do so when he tried without difficulty. But according to the FDR it was 18 seconds after touchdown before the reversers were engaged, which is a long time.I'll post the NTSB report in a new message.

[Guest tmetzinger]

************************************************************ NTSB ADVISORY************************************************************National Transportation Safety BoardWashington, DC 20594December 15, 2005************************************************************NTSB UPDATE ON SOUTHWEST AIRLINES RUNWAY OVERRUN AT MIDWAY AIRPORT************************************************************The National Transportation Safety Board today released the following update on its investigation into the accident involving Southwest Airlines flight 1248, a Boeing 737-700 on December 8, 2005, at Midway Airport in Chicago, Illinois. The airplane overran runway 31C during the landing rollout.The accident occurred about 7:14 pm central standard time. The airplane departed the end of the runway, rolled through a blast fence, a perimeter fence, and onto a roadway. The airplane came to a stop after impacting two automobiles. One automobile occupant was fatally injured and another seriously injured. The flight was conducted under 14 CFR Part 121 and had departed from the Baltimore/Washington International Thurgood Marshall Airport, Maryland. The on-scene portion of the investigation has been completed. Additional fact-finding, including tests and research, will be conducted at various component manufacturers. The Safety Board staff continues to examine the information provided by the flight data recorder and the cockpit voice recorder.Operations/Human PerformanceThe two pilots in the cockpit were interviewed on Saturday. Each interview took approximately three hours.The pilots stated that everything was normal through the point of touchdown. Approaching the airport, weather was of concern to them, and they listened to the ATIS (the recorded weather update) four times during the latter portion of the flight. They stated that they agreed with the dispatcher's assessment of the conditions for landing on runway 31C and backed up that assessment by inputting the numbers into the on-board laptop computer tool.The computer confirmed that the landing would be within the operational parameters of the airplane and Southwest's procedures, they said. Autobrakes were set on MAX, and they activated after a "firm" touchdown. 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. At some point, the Captain noticed that the airplane was not decelerating normally and applied maximum braking manually. The first officer also became aware of the poor braking effectiveness, moved his seat farther forward, and also applied maximum braking. They stated that they continued to apply maximum pressure to the brakes as the airplane went straight off the end of the runway and came to a stop.Interviews were conducted with a number of other Southwest Airlines flight crews, including the crew of the last Southwest flight to land at Midway and a subsequent crew that diverted to St. Louis.Airplane Performance Preliminary calculations show that the airplane touched down with about 4,500 feet of remaining runway and was on the runway for about 29 seconds. Preliminary calculations also show that, for the runway conditions and use of brakes and thrust reverser that occurred, the stopping distance without hitting obstructions would have been about 5,300 feet (the actual stopping distance was about 5,000 feet). In addition, had the airplane landing into the wind, rather than with a tail wind, the stopping distance for a landing would have been about 1,000 feet less.Documentation of aircraft performance from the scene has been completed to the maximum extent possible. It was not possible to observe tire marks from much of the landing rollout due to the fact that the aircraft landed on a snow- covered runway and snow fell on the runway immediately following the accident. FDR data show that autobrakes were active and provided high brake pressure upon touchdown. Autobrakes and manual braking continued to provide high brake pressure throughout the landing roll.FDR data show that thrust reversers were activated about 18 seconds after touchdown or about 14 seconds before contact with the blast fence. Testing and examination of the thrust reverser systems will continue.Investigators have obtained the laptop computer tool used by the accident flight crew. It will be examined and calculations of landing performance will be compared to flight manual data.Eleven security-type video cameras were identified on the airport that may show imagery of the airplane rollout or the surface of the runway and taxiway at the time of the accident. The videos will be reviewed.Meteorology National Weather Service forecasters and other personnel were interviewed. An enhanced snow band was in the area producing localized heavy snow due to lake enhancement. This apparently is a somewhat unusual weather phenomenon, as the band swath was only 20 to 30 miles wide with snow accumulations of 10 inches right over Midway Airport.Midway Airport weather observation equipment and records were examined and all equipment was working normally during the evening of the accident.Southwest Airlines dispatchers who were associated with the accident flight were interviewed. Prior to the takeoff from Baltimore, when weather conditions deteriorated and the runway switched to runway 31C, the dispatcher determined that runway 31C was approved for landing for flight 1248. Runway conditions, braking action, wind speed and direction, airplane weight and mechanical condition of the aircraft are typical factors considered in making such decisions. The flight was contacted twice on the way to Midway and the appropriateness of using the runway for landing was reaffirmed during both contacts.Official weather observations:Approximately 20 minutes prior to the accident, the winds were from 100 degrees at 11 knots, visibility was

[Guest D17S]

On the stabilized approach front, the pilot group I work with recently enacted a

[Guest tmetzinger]

>You can really help us with this. Thanks. >>So with brakes only (without the reversers) they would have>needed 5300 feet to stop? Right?No. According to the report, they rolled for 29 seconds before reaching the blast fence. If they hadn't hit anything, they would have needed 5300 feet with brakes coming on at touchdown, and the thrust reversers coming on 18 sec later (which is what happened). So if the runway had been 1000 feet longer they'd have been OK , EVEN with the thrust reversers being late. >>They only used brakes, but they managed to 'come to rest' at>5000 feet because they hit the fence too.They used brakes and reversers, but the difference between the 5300 predicted distance by the NTSB and the actual distance (5000) can be explained by the energy lost in the impacts.>However if everything had worked right, it SHOULD have only>taken 4500 feet to stop?No idea what stopping distance would be required if the reversers were deployed at touchdown - I expect that the NTSB will calculate that. I'm sure the distance that the dispatchers and flight crew calculated was less than the 4500 feet, but we'll have to wait to see what the NTSB says it would have been.>. . . And the airplane touched down with exactly that 4500>feet remaining? Still sounds like he landed long. There

[Guest Darren Howie]

Well it is good to hear from the report that the approach was not unstable as a contributory factor.My mistake for misreading an earlier post which lead me to believe it was a fast approach."Preliminary calculations show that the airplane touched down with about 4,500 feet of remaining runway and was on the runway for about 29 seconds. Preliminary calculations also show that, for the runway conditions and use of brakes and thrust reverser that occurred, the stopping distance without hitting obstructions would have been about 5,300 feet (the actual stopping distance was about 5,000 feet). In addition, had the airplane landing into the wind, rather than with a tail wind, the stopping distance for a landing would have been about 1,000 feet less."OK 31C at KMDW has a usable length of 5826'.With a TCH of 48' which aims to touch you down 1000' into the runway depending on slope we are down to 4800' of available roll out ground assuming you touch down on the 1000' markers.SO with the report stating the a/c touched down with some 4500' remaining the a/c landed some 300-400 to long to start with.Given that a credit IS given on contaminated runways for reverser usage it would NOT be possible to stop the aircraft given the combination of long landing and lack of reverser deploymant if it was close or at limit ldg weight.I mean if the reverse doesnt work you will not stop under ANY circumstances with good braking action.Contaminated runways is one of the few instances where reverser credit is given in performance charts as it normally is not.So here is the scenario.We are close to max weight(may even have been at max weight) for landing on a contaminated rwy with variable downwind(was that allowed for by dispatch?) in poor wx conditions on a runway which has reports of poor braking action.Mmmmmmm.Let me think of how long it would take me to say no thanks.Maybe the crew did not remember or dispatch did not remind them but the moment those reversers did not deploy immediately that aircraft was going to overrun that runway to some degree or another.Darren

[Guest capntom]

Missing so far is of course the flight recorder data and anaylisis. A critical item in landing on any minimum length runway (max performance landing) is the speed at touchdown. The energy that needs to be dissapated increses with the square of speed, so a small increase of groundspeed at touchdown (due to either excess airspeed or tailwind). Modern digital flight data recorders allow a very detailed anaylisis of a myriad of parameters. I worked with this as ALPA rep for FOQUA for my airline for a while.Max manual braking applies a greater braking effort than max autobraking. 737 (and other) reversers can be awkward to bring into reverse in some instances. Performance calculations for landing on this runway should have ignored the effect of reverse thrust (a bonus). As to touchdown, having occupied a rear (737) flight attendant seat before, it seemed that the firmness and decelleration of a normal landing were magnified over what is felt in the cockpit. Add a few knots airspeed, wind transient at 10 knot tailwind or so, touchdown just a snitch long, what's considered possible, with appropriate saftey factor, moves over the edge.Braking action reports or measurments?It's never just one thing.

[Guest D17S]

Boy. I'm with you. This sounds like an accident even before it happened. As you describe, if the landing is calculated with reversers inop, they're off the end under any circumstances. Something else must be happening here. But what? It sounds like even an optimum rollout length of 4900 (5900-1000) with everything working would still be right on the edge. This means the nose wheel hangs over the edge of the asphalt run-off apron as the airplane finally come to a stop. Would SW be authorized to power back their 737 to get back to a turn-off . . . or would they have a tug standing by? Pilots. . . There are charts that calculate rollout distances for airplane configurations in weather/condition configurations. That will give a number, "X feet to stop." What's the safety factor distance beyond "X" that must exist to allow a landing? Consider the numbers given so far. The NTSB is saying that the airplane could have stopped in 5300 feet given what actually happened (nominal brakes and late reversers). Let me interpolate a bit (i.e., make a wild guess only for the sale of an example). If the reversers had deployed on time, that might have shortened the landing by what, 200 feet, 400 feet? Now adding it up. Now we have a landing that needed 5300 ft (what happened) - 400 ft (reverser 'on-time' savings)= 4900 feet. Now how much

[Guest joediamond]

>Pilots. . . There are charts that calculate rollout distances>for airplane configurations in weather/condition>configurations. That will give a number, "X feet to stop.">What's the safety factor distance beyond "X" that must exist>to allow a landing? Part 121 rules require that the aircraft be able to land and stop within 60% of the available runway.For example if the actual landing distance required is 4000 ft. the runway would need to have an available distance of 6667 ft. to be legal.C McCarthy

[Guest D17S]

That sounds reasonable. So if they thought they would need 5000 feet of roll-out room, a 5900 foot runway isn't even close. Or said another way, for a 5900 foot runway, (59X60%=)3500 ft is the maximum rollout projection allowable. The NTSB has 'em at a 5300 foot rollout with just a little late reverser action. On-time reversers (i.e., ~15 extra seconds of reverse thrust) would have saved 2000 feet (~37% of the actual roll/crash) and stopped the airplane safely in ~3500 feet of runway usage (the ~60% rule)? Did anyone see that video where a C-130 fired off reversed JATO packs for a short field landing demo?

[Guest tmetzinger]

Sam, I'm not sure how you consider 18 seconds "a little late" - they were more than halfway down the runway at that point. Reversers are normally activated within a second or two of touchdown, so this time they took NINE to EIGHTEEN times as long to activateThrust reversers are most effective at high speeds, so the earlier they deploy the more difference they make. I have no doubt that timely deployment of the reversers would have made a large difference and probably saved 2000+ feet, and I expect that when the NTSB releases it's report they'll say something to that effect.Since we know that both dispatch and in-cockpit calculations found thr runway acceptable, the crew had reason to expect that the stopping distance with normal operations would have been within the 60 percent rule.

[Guest tmetzinger]

To Darren and Tom:Reported Braking Action is the one thing not mentioned in the NTSB report. While the touchdown speed is not mentioned, they do mention that they've looked at FDR data and I am comfortable assuming that if the touchdown speed was out of line it would have been mentioned. So I think the approach and touchdown were within limits. If so, the cause of the accident becomes the aircraft's failure to stop within the expected distance. We know that the brakes were working, we know that the reversers were late. We know the weather was crappy, but we DON'T know how slick the runway was.Based on the media's report, the last official word from the tower was that braking action was "good". So, Darren, if you were flying in those conditions, and you had a report of "good" braking action, would you land or divert? It seems that the numbers (credit for brakes and reversers) would make the runway acceptable if braking action was "good".There were media reports that other aircraft reported "fair to poor" braking action, but we don't know if SWA heard them or not - they may have been talking to approach at the time and they may not have been relayed. I'm willing to give the crew the benefit of the doubt so far on their decision to attempt the approach. To sum up - if the crew got a report of braking action being less than "good", then the decision to attempt the landing becomes questionable. If they didn't get such a report, then the focus really shifts to why the airplane didn't behave as expected. The things we can focus on based on the NTSB data so far are:Late reverser deployment (human error or mechanical problem)Actual runway braking action (weather if condition not known, failure on the part of ATC to relay actual conditions if they were known).

[Guest]

Why the heck should you want to sue the airline "because I wet my pants"?Only in litigation happy America...Laws against frivolous lawsuits should be far far stricter. Even if you were hurt you should not be allowed to sue unless the airline is determined as the responsible partner and can be proven not to have taken suitable (as defined by law) effort to prevent the accident and help those affected by it.Anyone loosing a lawsuit they bring should furthermore be required to pay the defendant the same amount they demanded.That should stop a lot of the idiotic claims.

[Guest]

Seems to happen an awful lot, more than can be explained purely by statistics.Whether official policy or making an easy job of it (can't find the cause in 2 weeks, claim pilot error, type of attitude) doesn't matter.

[Guest WesFlight]

100% Agree :-)