SAFO 15009
Discussion: The root cause of the wet runway stopping performance shortfall is not fully understood at this time; however issues that appear to be contributors are runway conditions such as texture (polished or rubber contaminated surfaces), drainage, puddling in wheel tracks and active precipitation. Analysis of this data indicates that 30 to 40 percent of additional stopping distance may be required in certain cases where the runway is very wet, but not flooded. |
#159, without details of performance ‘tools’:- what is the basis of calculation, origin, who published them and the guidance for use, suggests weak knowledge ‘in the workshop’.
Blunt or rusty ‘tools’ are of little value; a key point about landing distances is that they are approximate (never really sharp), and that accuracy decreases with increasing ‘wetness’ and contamination. Technical variation can be estimated, but the human contribution less so, especially in new or novel conditions. The conditions in each landing differ, we never experience the same landing twice; past comparison is of lesser value, but the lessons learnt should be, providing they are applied to the next landing. Tools are best used by skilled craftsmen, according to circumstance, judgement - ‘the right way to cut the grain’. BA ‘good’, is good relative to a wet runway. Wet performance is a projection, an estimate based on dry runways, which have a different version of ‘good’. Consider how performance tables might accommodate the range of water depths up to 2.99 mm, but differ where 3 mm is defined as flooded (% of runway covered). The tables do not cover every combination, particularly when we consider runway surface texture, tyre wear; that’s why we have regulatory advice and the need for professional knowledge, and above all else the ability to apply professional judgement. CT, I support your underlying view, but please there is no ‘legal’ value in performance, nor perhaps in anything we do in aviation. ;) There are required or recommended values, and most important, justifiable choices of action - these are the basis of your defence. There is nothing legal about sitting in EMAS quoting book figures when the lawyers are speeding down the runway behind you, measuring the actual landing conditions (‘legal’ hindsight), and forming their judgement on how you handled the situation and aircraft. |
Reluctant Bus Driver Thank you for your info. I just googled the available landing distance since I don’t fly there. With the numbers you came up with, a legal landing is not possible with our -700s. I don’t know the technical details of SWA aircraft, and the landing weight was a guess. My numbers are raw numbers and do not include the legal margins. Add those on your runway lenght and this landing is a no go. |
ManaAdaSystem
I'm curious, does this actual landing distance include distance to the touchdown point? Which margin do you normally have to add in your operation? (Just being curious here so the numbers have some more meaning for me) |
Yes, they include air distance to full stop. As for the additional margins, some performance buff will probably come along with the explanation, but if i remember correctly, wet runway add 15% to the required dry landing distance. If you operate in Germany, you follow the same rules as me. I just can’t be bothered to dig into the books at the moment. |
Regardless of the theories posted here, I hope for the sake of the SWA crew, that their landing data was calculated correctly and that they touched down in the touchdown zone. If they did not do the data or ignored it they will be in a lot of trouble. It's a similar scenario to the AA 737 that went off the runway in kingston where there was no EMAS and the aircraft was destroyed. The crew is back on the line and had no enforcement action against hem because the NTSB and subsequently the FAA stated they acted in accordance with all procedures and did not know of the standing water on the runway. I hope this will be the case here as well..
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RBD
Agree re performance data. Is the 737 landing performance now based on OLD / FOLD calculations opposed to the old style ‘actual’ data. The wording in some posts suggest the latter, if so then either Boeing - tardy publication revision, or Operator - not using the best available data, might get a hard time from the FAA. Re standing water; there are subtle differences between not knowing due to inaccurate surface descriptions, or if reported not ‘knowing’ because the previous information was not checked, based on what could be deduced - WXR etc, also not knowing or not seeking the best data at all. The dividing line of professionalism. Where crews have followed procedures, this should not be taken to imply that the procedures are sufficiently accurate or have considered a wide range of situations. CS 25.1591(~page 199) and particularly CS AMC 25.1591 (~page 878) give salutary enlightenment of the limitations in calculated performance. Of note, these sections do not appear in the corresponding FAA documentation - non harmonised rule making. |
@ hans, 172 (and C/A)
Both 737 and 320 have quite a similar landing geometry. If the antenna passes THR on the G/S at 50', later the MLG will cross at 33' (34) which should be the RA indication (calibrated that way). The radio call "over the numbers" should be 30 (not 50 btw) - the normal landing technique for the expected touchdown point at 455 m (1490 ft). Irrespective of LDA. Runways >= 2400m are a small cognitive challenge due to the placement of the large distance marker and PAPI (nicely documented by the incumbent's almost contradicting statements above). The no-flare point is 200m (-ish) plus another 255 m (835 ft) is calculated for the flare. That's a fair deal. On a good day, a 400 m touchdown is perfectly possible while keeping the normal profile. 350 surely too with a thump :) Re-iterated: To fit the actual trajectory inside the calculation model, no extra skill or fjord-pilot tricks are required. video: https://www.youtube.com/watch?v=j2WHVjP60Gg&feature=youtu.be&t=330 54' TCH/RDH, aim-point 314 m deep (nominal 3°) 35' RA when wheels over the THR 4 reds on the PAPI (displaced 470 m) at the round out and touchdown exactly abeam https://www.google.com/maps/@48.9931.../data=!3m1!1e3 However, the plot thickens in the second act where the relationship between the actual achieved vs. calculated deceleration needs to be discussed. ManaAdaSystem:I'll pass on the measuring exercise, yet for my improvement: Which of these I actually said do you disagree with?
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One thing comes to my mind regarding this conversation. Why is the First Officer not the Captain? If decisions around takeoff and landing performance ( along with hundreds of others) were simply a matter of checking the data and seeing whether it said yes or no, then plenty of 19 year old bright young things would be employed to operate the airliners flying around the globe. The reality is that the regulator and the company have determined that the aviation environment has too many variables for this to work. For safe operation there needs to be an experienced person in the flight deck with the authority to say yes or no regardless of what the computer says. To abdicate decision making to the onboard performance tool is to disregard that reality and the paying passengers and their relatives would rightly feel uncomfortable if they were aware of this happening. As technology becomes faster, more accurate and more reliable, are we less inclined ( as Captains) to exercise our command authority based on experience? I think so. There are examples of it on this thread. If we are less inclined now than thirty years ago, where does that leave us twenty years from now? There will be Captains who have witnessed extremely reliable technology their entire lives, there is every chance of increasing reluctance to over ride or even question it’s solutions. I think we need to be aware of this tendency within ourselves and actively question the common sense element of our decision making and consider what the passengers, company, and regulators expect of us. |
One of the most pertinent contributions to Prune I have read in quite some time. It does touch on some pretty profound philosophical considerations. |
Have not every post on this long thread.
My thoughts (and actions in the cockpit) is that a short runway, tailwind, or wet runway require vigilance. Having two of these together requires an extra amount of vigilance and thoughts of holding or diverting, All three, is realistically something you don't want to subject yourself, crew and pax to. A 5800 foot runway with numbers that give just a margin of just a couple of hundred meters is unacceptable. Heavy rain may mean that the braking action and reported winds are incorrect. Don't know all the facts in this case, but everything reported does not seem to point to landing in these conditions. |
ManaAdaSystem BUR RW 8 is 5802’ long not 6500’. Using medium or a 3 for braking action that +R would require I can’t make the numbers work for a 700 with a 10 knot tailwind. |
Originally Posted by Reluctant Bus Driver
(Post 10336041)
As some have alluded to, the usable landing distance, assuming they did not go below GS, is 4575ft. Not much to hang your hat on..
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Sailvi767 Is 3 automatically required for heavy rain? Does that override the airport’s current field condition report? |
Not at SWA anyway. Heavy rain is a weather condition, not a runway condition. You could always argue to use a more conservative setting than is being reported, but you'd still just be guessing. There's a table in the back of our AOM that provides a relationship of runway conditions to RCC values. Wet is damp or standing water up to 1/8in, RCC 5. There's also a slippery when wet for excess rubber, RCC 3, which is probably what they actually had and if it was reported would most likely have prevented them from attempting to land. But when you're given an RCC of 5 and "braking action good" by the Tower it's hard to argue with their decision based on what they knew at the time.
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The report of the rain increasing to +R should cue any crew to downgrade to medium braking for calculations. |
Sig, interesting views.
Because ‘slippery when wet’ is additive, not directly related to weather or runway contaminants, it might be better used to reduce the assessed braking action; select the next lower value. ‘Tower’ information is advisory; it might be the best assessed or calculated, or their best guess by looking out of the window, worst still, incorrectly passing on a PIREP. None of these remove the need for reassessment according to the situational conditions. Some operators have a rule of thumb which linked any red WXR over the airfield in the preceding 15 min, to the assumption of a flooded runway. Risk is not determined by assessing what is known, it’s the understanding of what is not known and possible consequences of the knowledge gap. |
At my operator, +RN equals a Runway Condition Code of 2. That would limit the tailwind to 5 knots. However, the braking action report of GOOD from the preceding aircraft could have upgraded the BA to GOOD and possibly allowed the landing, depending on weight. |
Unfortunately, we'll never know.
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One of the first posts in this thread quotes aviation-safety.net's web page that claims "Aircraft damage: Minor". It looks like the cowlings are resting on the ground, although aerial views online do not clearly show scrap marks on the EMAS blocks, with blocks costing around $2000 each average, not including labor. Is there anyway this accident is minor, or does a minor accident go up to a few million dollars in repair costs?
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I bolded the most relevant parts pertaining to NTSB 830 reporting requirements. Major repairs are defined in CFR 14 part 43 and require a properly filled out and signed form 337. The completion of this form constitutes the approval of the repair by an appropriately qualified and authorized inspector and becomes part of the aircraft maintenance record.
Originally Posted by NTSB 830.2 (definitions)
[edited for brevity]
Aircraft accident means an occurrence associated with the operation of an aircraft which takes place between the time any person boards the aircraft with the intention of flight and all such persons have disembarked, and in which any person suffers death or serious injury, or in which the aircraft receives substantial damage. For purposes of this part, the definition of “aircraft accident” includes “unmanned aircraft accident,” as defined herein. Substantial damage means damage or failure which adversely affects the structural strength, performance, or flight characteristics of the aircraft, and which would normally require major repair or replacement of the affected component. Engine failure or damage limited to an engine if only one engine fails or is damaged, bent fairings or cowling, dented skin, small punctured holes in the skin or fabric, ground damage to rotor or propeller blades, and damage to landing gear, wheels, tires, flaps, engine accessories, brakes, or wingtips are not considered “substantial damage” for the purpose of this part. Substantial damage means damage or failure which adversely affects the structural strength, performance, or flight characteristics of the aircraft, and which would normally require major repair or replacement of the affected component. Engine failure or damage limited to an engine if only one engine fails or is damaged, bent fairings or cowling, dented skin, small punctured holes in the skin or fabric, ground damage to rotor or propeller blades, and damage to landing gear, wheels, tires, flaps, engine accessories, brakes, or wingtips are not considered “substantial damage” for the purpose of this part. |
edmundronald
That is a comforting sentiment to entertain, but in the real world, a pilot who diverts to an alternate in order to avoid a landing that the data supports will most certainly get a phone call from his base chief pilot asking him to explain himself. This implicit pressure certainly can cloud judgement. Unfortunately, the aviation industry employs "binary decision making" (i.e. there is no spectrum of safety, an operation is either safe or unsafe, no grey areas are acknowledged). |
LDW
My operator uses LD*SAFO +500'. I'm very happy to report that we're unlikely to get a phone call for making a prudent decision in marginal Wx.
Either the environmentals were incorrectly reported in this case, or the jet didn't land in the right place. I know Burbank is closer to many peoples destination than LAX, but this was taking things a little too far... As an aside, I watched Mike Pences' 737 steer round the EMAS in LGA one rainy night. Luckily the six lane Grand Central Parkway was there to absorb his overrun...Some wit photoshopped the Vice Presidential Seal on a satellite picture of the EMAS.... |
Perhaps at SWA, but not at most airlines on that runway with the weather at the time.
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NTSB Accident Docket opened: NTSB Docket - Docket Management System
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(*) in detail here what followed:
Originally Posted by CVR
0901:36.2 BUR wind two seven zero at one one.
0901:41.3 HOT-2 #. 0901:43.2 HOT-2 er there's five hundred. 0901:44.8 HOT-1 roger. 0901:48.9 HOT-1 we need some kind of lights. I got some lights. 0901:51.6 HOT-2 alright we got eleven knots. you want to call it good? 0901:54.5 HOT-1 yeah. |
Originally Posted by 737er
(Post 10330765)
Im just trying to keep it real here regarding the specific issue of did they think they had an 11 knot tailwind component and just landed anyway. To that I’d say it’s monumentally and fantastically implausible.
The Aircraft Performance Study in the Accident Docket has this analysis: Reported vs. actual wind conditions The maximum tailwind allowed by the SWA AOM is 10 kt. The tailwind component corresponding to the wind report provided by the ATC tower at 09:02 (wind from 270° (magnetic) at 11 knots) is 10.8 kt., i.e., higher than the limit. However, the Captain stated in his interview that he and the First Officer “acknowledged this call and agreed that the tailwind component was 9-10 kt. and it was within limits.” The error in the crew’s estimate of the tailwind component is admittedly small (about 1 kt.); consequently, it is possible that if the winds reported by the tower had been more consistent with the winds recorded by the ASOS (and computed using the FDR data), which were 3 to 5 kt. higher than those reported by the tower, the crew might have recognized that the AOM tailwind limit was exceeded and abandoned the approach. The higher than expected tailwind, the longer than normal touchdown point, and to a lesser degree, the faster than nominal approach speed all contributed to the overrun. However, of the three, the long touchdown is the most significant contributor. The airplane could have stopped on the runway with the high approach speed and tailwind even if the touchdown had been 312 ft. longer than the nominal 1,500 ft. from the threshold; however, with the actual touchdown point of 2,504 ft. from the threshold, either the tailwind or faster approach speed by themselves would have prevented a stop on the runway. Per the SWA AOM, once the airplane overflew the nominal 1,500 ft. touchdown point, the PWB landing distance calculations became “invalid” and “a go-around [was] the better option.” 0824:52.9 HOT-2 yeah it's wet with a tailwind...and # short runway. 0824:58.3 HOT-1 awesome. 0825:00.0 HOT-2 yeah that's great. what could possibly go wrong. |
Originally Posted by Airbubba
(Post 10988952)
They did discuss the threats in the briefing.
I tend to imagine it with a sarcastic touch, but what if the pilot behind HOT-1 was actually excited about this challlenge? The pilot behind HOT-2 was far more afraid, yet didn't speak up for busting the OM limit and calling for a go-around. |
Contrary opinion here. The HOT2's indistinctive relay of information and downplaying tone greased the stairs.
Clear, unbiased and precise delivery of support facts is the true responsibility of the PM and that has completely failed here. Although we do not see the whole story, why he communicated in such an inadequate manner. Tangent question: If there was a SIM scenario where tailwind would gradually increase from 7 to 20 knots (assuming limit at 10) below say 400 feet once visual after breaking the cloud, and the PM failed to speak up that the landing must be discontinued,... is it a fail-and-retake situation where you work? Probably it should be, it is a two-pilot operation after all, yet my bet is there is no such general training practice. Certainly have not experienced one like that. Regardless of the above, the crew was illegal to start lt the approach with regards to LDA under the reported wind conditions. No lessons learned from the previous overrun. The only topic left to discuss is if they did, what will prevent me doing the same as well. 1) Clarify to oneself the difference between the so-called and useless touchdown zone definition (shortest of 900 m or 1/3 runway) and the acceptable touchdown point from the stopping performance viewpoint: THR plus 400 m +/- 200 or 1200 ft +/- 600. Going beyond the target of 1500 ft / 500 m starts to remove the first protective coat and losing three of them will put the naked truth on the front page. So, train your mind thoroughly to execute a G/A when landing deep. Let there be no doubt the subconscious WILL play your rational self very dirty, same as it did to the skipper here. There will be zero defences not do the stupid thing. Raw sensory information that will trigger an automated escape drill is the only hope for cases where the PM is gone missing. If you happened to step over any lines in the previous moments no matter how thin and formal, do not expect the F/O to speak as the plot thickens. It's the human nature to stay put and be a good boiled frog. In pilot speak: No landings beyond the last distance markings! Be acutely aware that PAPIs must be disregarded as a general rule because many of them mark for an aiming point that is already on the far edge of where the touchdown is permissible. 2)... passing on to the next contributor.. |
YouTube: Southwest Airlines 737 Runway Overrun at Burbank
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I notice in the video at 1:10, there is a flash on the left side, which might have been a compressor stall. Is that to be expected if you apply max reverse when moving slowly?
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