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B737-800 aquaplaning at Christchurch New Zealand. Excellent report
https://www.atsb.gov.au/publications...r/ao-2015-046/
Well worth reading. The crew did everything right but were caught by surprise by aquaplaning conditions during the latter part of the landing run. |
The report hints at the reason, FAA SAFO 15009 explains: Purpose: This SAFO warns airplane operators and pilots that the advisory data for wet runway landings may not provide a safe stopping margin under all conditions.
In a nutshell, the FAA SAFO are saying wet runway landing distance including factoring isn't sufficient to cover you behind. A training Captain once mused to me about a hypothetical exchange between a prosecutor and a Captain in the subsequent court of inquiry: "So Captain, was the runway wet or dry" "the runway was damp, therefore the manual says it could be therefore considered dry" "Captain, If you sat on the runway, would your bottom be wet? No further questions your Honor" |
CT, you've linked to the wrong SAFO. In any case, I don't think the SAFO has anything to do with this.
The problem was, due to company policy, they used Dry figures on a Damp runway. The "Damp" runway chestnut rears it's ugly head again. They should have used the "Good braking action" figures. ;) |
The problem was also that the "damp" runway was largely wet.
I disagree that the 15% additional factor is not enough, it seems it is spot on. ;) |
The crew did everything right Company changes the book. Runway is “damp” and dry numbers say it’s tight but ok and wet numbers say no go. You get paid to say no. |
The relevant SAFO is 15009, but linked here. http://www.faa.gov/other_visit/aviat.../SAFO15009.pdf The FAA AC for pre landing runway assessment is here. http://www.faa.gov/documentLibrary/m...5-32_Final.pdf Aero, #4, re 15%, it depends which 15% is being considered. If based on certificated Landing data; 1.15 dry distances for wet, then ‘this 15%’ may be insufficient in many situations. The FAA SAFO appears to relate to this, but caution because their ‘manufacturers actual’ distances (Boeing term) is not the same as AFM certificated distances. Post TALPA and using Operational Landing Distances (OLD) which provide a more realistic view of achievable landing distance (actual); then manufactures and regulators (FAA AC) recommend a further 15% minimum addition, often published a Factored OLD (FOLD). This 15% should relates more closely to what happens in day to day operations on wet runways. However ‘how wet is wet’, there are some, many combinations of water depth, runway surface, tyre/brake condition, etc which warrant use of more than 15% minimum addition. Some of the technical aspects are here https://skybrary.aero/bookshelf/cont...hp?bookId=3841 |
To me, "damp" = wet, since it is not as good as dry. How much less good? I don't know, so that's why I'll err to the safer side.
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I have aquaplaned in a 737 NG and it is not pleasant. The crew were put in a difficult position with the workload pretty high. I found the report frustrating in that it didn’t bother to mention the Runway length until quite late in the picture. Once I eventually found it was only 1700m, I was very surprised that they chose Autobrake 3 rather than Max as the NG is not a good stopper. I also couldn't see see whether they had Carbon or Steel brakes? |
To me, "damp" = wet, since it is not as good as dry. How much less good? I don't know, so that's why I'll err to the safer side. A good working knowledge of the terminology, phraseology, factoring techniques, data sources and SOP’s was much more difficult to maintain in 2015 when this occurred, than it has been historically, because of A/ ambiguity between source documents and B/ large scale change of methodology We are probably starting to get to grips with TALPA a bit more now but still, a conservative, sensible, and simple approach from individual pilots as displayed by Intruder above is our best defence. The reader of this report will finish it unaware that many New Zealand line pilots were concerned about runway performance in NZCH during the runway works at this time and it appears that Air NZ had elected not to use 29 prior to this incident. Good on the crew for stopping it 5m before and not 5m after. |
Way back when, before introduction of anti-skid protection, aquaplaning (I seem to remember it was more commonly called hydroplaning at least here in US) was not uncommon. In severe cases the tire rubber would melt and it was explained that the braked wheel raon atop superheated steam which literally melted the tire rubber. Antiskid systems and Maxerets mostly stopped that extreme result except when there were maintenance faults such as crossed brake lines (or wiring) on a bogie type gear.
Runway braking reports are problematical. Back in late 1970's when Maintenance Manager for EAL at KEWR, I would get weekend duty. On snowy days the Port Authority would come and pick me up at my office and take me out for a trip down the active runway or runways. I was supposed to rate the braking action from the non-driver seat of a speeding Police car. Being a conservative fellow my fair/poor braking condition ratings sometimes made the Airport Operator unhappy. I hope they have come up with better ways of rating than in those now pre-historic times. |
While this may have been a close call how can it be classified as an ’incident’ ? After all they did not overrun the runway |
You’re right Stilton, it didn’t overrun therefore it is not an accident. It can be classified as an incident because it meets the ICAO definition of a ‘serious incident’. An incident is defined as: An occurrence, other than an accident, associated with the operation of an aircraft which affects or could affect the safety of operation. Note.— The types of incidents which are of main interest to the International Civil Aviation Organization for accident prevention studies are listed in Attachment C to Annex 13. A serious incident is defined as: An incident involving circumstances indicating that there was a high probability of an accident and associated with the operation of an aircraft which, in the case of a manned aircraft, takes place between the time any person boards the aircraft with the intention of flight until such time as all such persons have disembarked, or in the case of an unmanned aircraft, takes place between the time the aircraft is ready to move with the purpose of flight until such time as it comes to rest at the end of the flight and the primary propulsion system is shut down. Note 1.— The difference between an accident and a serious incident lies only in the result. |
The captain assisted the FO with manual braking. Both crew reported that they could feel the rudder/brake pedals ‘pulsing’, which indicated the antiskid system was operating. The crew elected to keep reverse thrust deployed to assist with braking. The FO reported that he was focusing on the red runway end lights and noticed the aircraft drift slightly right, which he then corrected to bring the aircraft back onto the centreline. We all know it can be quite distracting to the PF to feel the other pilot riding the rudder pedals. A case perhaps of the FO thinking who is flying this machine? If the captain was that concerned the FO was not applying enough braking (otherwise he would not have felt the need "assist" him in manual braking), it would have been better for the captain to call "I have control" and finish the job himself. You can't have two Bob's each way in a situation like this? The ATSB reporter who wrote the final draft seems to have missed that fact that both pilots applying brakes simultaneously but not evenly, could have confused the anti-skid system and perhaps inadvertently extended the landing run? |
Way back in the late 70's operated a Sabre Liner, no anti skid brake and very narrow wheels, right off an F-86. The check out included a simulated wet runway. The idea was to basically plant aircraft on as close to the end of the runway with a rather firm plant, then cut of one motor (no reverse on these old ladies) and apply brakes. If a skid developed, release the brakes and reapply. As I learned after more than several hundred hours, a plant on a rain covered runway was actually much closer to soft and it worked. If you spent enough time on this aircraft you would skin a tire. I moved on before that happened to me. So, when landing on a wet runway, a plant it good, the payers in the back will think it was a greaser. End result of the plant is less moisture between the rubber and the concrete. The same idea apply for landing on icy or snow packed covered runways. Easier to say sorry for the firm touch down than start a discussion with the Chief Pilot or Safety Board.
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PEI, my comment about the 15% being just enough was with tongue in cheek.
Mustangsally, the 737 didn't encounter wet conditions until partway down the runway. Touchdown technique would not have made any difference. Tee Emm, I had the same thought. Easy to say with hindsight of course, but I'm sure the crew have had a good think about a few of the aspects of the incident. |
Something is missing in all this. DONT land on Rwy 29 in marginal conditions when Rwy 02/20 is available. ATC in NZ an OZ have a very bad habit of allocating runways that are inappropriate for traffic/noise abatement/ATC convenience.Hardly a day goes by in YSSY that heavy longhaul carriers or allocated Rwy 25/07 due noise abatement when the wind is straight down Rwy 16 and wont get a runway change unless the say "require" instead of "request". Same in YMML regarding Rwy 27 vs Rwy16. When a Chinese low cost operator goes off the end of the runway with a 15 knot crosswind and damp runway the subsequent inquiry will be a ripper.
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02/20 wasn't available*. Previous A320 diverted rather than landing on 29.
* Or rather, it was only available in one direction and the tailwind and shortened length made it worse than 29. |
Why would any operator let alone the regulator accept actual ldg dis + 15 % for inflight reassessment unless a non-normal presented itself, and there wasn't an alternate available.
Edit: Dumbfounded by the dry / damp / wet bit as well. There is no such thing as damp other than here, NZ and maybe PNG, plus from my experience ATC is somewhat lax in down or up grading rwy conditions. |
It’s not actual + 15%, it is actual x 1.67 for dry and actual x 1.92 for wet. 1.92 is 1.67 x 1.15 which is where the 15% figure is coming from. |
It’s not actual + 15% |
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