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BA 787 Nosewheel collapse @ LHR

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BA 787 Nosewheel collapse @ LHR

Old 19th Jun 2021, 20:19
  #61 (permalink)  
 
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Ngineer

I got your point - good post. I also suspect the answer may be up a different tree, especially given the system complexity of the 787!
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Old 19th Jun 2021, 20:44
  #62 (permalink)  
 
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Lyneham Lad

Reliably informed by Boeing engineer friend that this would have been to test gear solenoid function. Lock pin in, and WOW breaker pulled then gear up selected. Locking pin correctly positioned would have resulted in a non-event. On the plus side, they can now mark the solenoid test "satisfactory".... however.....
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Old 19th Jun 2021, 21:01
  #63 (permalink)  
 
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172_driver

"Not 787 rated but I guess the design of the gear lock pins is pretty universal. Do they depressurize the hydraulics in the retract lines or do they physically prevent the down lock from moving (with hyd. pressure on)?"

Downlock pins (as opposed to steering lockout pins) typically don't interact with the hydraulics and simply provide (indirectly) a mechanical resistance to gear retraction.

Here's an example (actually a MLG, but the same principle applies to nose gears):



The gear isn't quite fully deployed in this shot - when it is, the two highlighted beams pivot so that they are in line with each other and form a geometric lock. You can just see the two holes that will then line up and if needed, accommodate a ground lock pin.

When I first encountered gear pins many years ago, I wondered how a relatively small pin could resist the force of a massive retraction jack - but of course they don't have to, all they need to do is to maintain the geometry of that downlock brace.

See post #22 for the pin in situ.
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Old 19th Jun 2021, 21:18
  #64 (permalink)  
 
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Thanks Dave, good picture!
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Old 19th Jun 2021, 22:15
  #65 (permalink)  
 
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Seems `bloody` stupid to do this test with crew on board,as Murphy would say....If it can go wrong,sooner or later it willl......
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Old 20th Jun 2021, 00:25
  #66 (permalink)  
 
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Firstly, we have to do a lot with Crew onboard when you are part of a system trying maintain an operation as well as the aircraft. Try turning an A380 on a 90-120 min turn round. The outbound crew are usually on the flight deck by the time I have done my external checks so anything that needs testing will get tested with Flight Deck, Cabin Crew, red caps, cleaners, caterers and even pax all onboard. If I need the Captain or FO to move, I'll ask. I'll gauge what other options I need to consider based on the test I'm running. In this case, assuming the pin was fitted and all other conditions met, I wouldn't have a problem with crew onboard, but would advise them what I was doing, and most of the time the crew are actually interested to see what we do and what the test does. If you want to avoid this situation, then aircraft will need say a scheduled 4 hour turn round time just in case we need to run tests - good luck getting that implemented by an airline. That is the system we work in.

Secondly, I don't think the Engineers were expecting an outcome like this, so why wouldn't they let the crew do their pre-flights as per usual. If the pin was fitted in the wrong hole, they were not aware and carried on potentially "knowing" that they had seen a pin or flag in the NLG & MLG, or had asked one of the engineering team to put the pins in and got confirmation. If we presume the WOW eCB was tripped and collared as per the test procedure mentioned, why would they expect this outcome? So it comes down to holes in the cheese lining up - a design issue which led to a mistake made, and maybe in addition not following the procedure (I'm not 787 licensed but I do work on them occasionally so know it is far from perfect and just plain weird at times, so not sure of the BITE process for satisfaction of pre-conditions prior to the test running i.e, does the WOW eCB need to be tripped to allow the test to continue?).

Note - paragraph 2 assumes this incident is due to the discussed issue of being able to put the locking pin in the apex pin and not the correct locking point.

Last edited by Tom Sawyer; 20th Jun 2021 at 04:30. Reason: add info
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Old 20th Jun 2021, 01:41
  #67 (permalink)  
 
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DaveReidUK

Yes, sorry to interrupt the wild speculations and nonsensical theories regarding aircraft towing that was running rife. As you were.
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Old 20th Jun 2021, 06:08
  #68 (permalink)  
 
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I remember similar designs on other A/C where the pins would fit multiple adjacent holes and we were taught never to put the pin in a hole with a collar. Clear markings, blockers and different diameters should be mandatory as some of these pins need to be fitted in locations that are not easily accessible, dark, etc., so possible mixups will occur sooner or later.

Best solution was on the Dash 7/ 8 were you’d have to lie down to insert a pin and pull out a panel on the nose section instead that effects the locking.
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Old 20th Jun 2021, 10:03
  #69 (permalink)  
 
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If a lot of airlines had not been flying freight for the last 18 months they would not have survived.
Freight can be light in weight and cabin loaded as well as heavy and in the holds.
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Old 20th Jun 2021, 10:33
  #70 (permalink)  
 
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Ngineer

I would be very wary of making blanket statements and assuming that what happens in your company is industry wide. For example in my last company it was a regular occurrence for me to arrive at the aircraft to sign off the fuel 15 minutes to departure and find the gear pins still fitted from the tow about 3 hours earlier - I actually preferred that as I ensured that, as the Engineer clearing the Tech Log entry, all pins were physically removed from the gear.
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Old 20th Jun 2021, 11:01
  #71 (permalink)  
 
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Tom Sawyer

Tom has hit the rivet square on the head (as always)
Its not unusual to end up having to get rid of a status message on departure and the 78 is no stranger to those, with the added bonus that a lot of BITE functions are inhibited with the refuel panel open which doesn't do much for the time pressure factor.
I can picture exactly how this was playing out because it could easily have happened to me or one of my colleagues. From the comfort of my sofa it'd be easy to say "well I would have triple checked the pin was in correctly" but when you are juggling 4/5 aircraft with varying levels of work on them and the distraction of an ever closer departure time, crew, dispatchers etc on your back then it becomes easier to see how the holes line up. (no pun intended)
I sincerely hope those involved are not castigated for this and important lessons are learned.
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Old 20th Jun 2021, 12:30
  #72 (permalink)  
 
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Hmm. If the possibility of a gear pin wrongly fitted was known about and indeed publicised, there’s not much of an excuse for still fitting the pin in the wrong hole? Surely if you are then going to run some checks where the correct fitting of that pin is all that stops the leg retracting when commanded to do so, you’re going to go back outside and check all 3 are correctly fitted!

Irrespective of the various holes present, doesn't simple physics give you a big clue as to where a locking pin should be fitted to do its job?
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Old 20th Jun 2021, 12:52
  #73 (permalink)  
 
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Well in an ideal world yes, however anyone who has fitted a jumbo downlock fishing pole may disagree with you there!
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Old 20th Jun 2021, 12:52
  #74 (permalink)  
 
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OldPilot71

Thank you (and others) for clarification on the why's and wherefores of likely events leading to the accident.
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Old 20th Jun 2021, 14:49
  #75 (permalink)  
 
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H Peacock

That all depends if the information has been disseminated all the way down the food chain so to speak in the airline concerned.

Who fitted the pin, what level of competency/training they have and which way it was inserted(from the left or from the right)also has a bearing on the outcome due to the differing diameters of the offending hole.

The FAA AD and it's subsequent rectification was raised because it is a known issue.
Not all airlines have embodied the mod yet.

You might like to read up on the EVA B744 nose leg collapse at LHR or a similar occurrence which happened to Lufthansa at FRA.
The nose gear pin was fitted in the correct location in both those incidents.

Also, the B747-100 incident at BAMC where HF came into play big time and resulted in the main body gear partially collapsing.
However before the gear checks began, the U/C pins had been checked by an experienced engineer.
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Old 20th Jun 2021, 15:04
  #76 (permalink)  
 
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Which brings us to the concept of ďJust CultureĒ, which in Western aviation is very well advanced. Here is a link that explains the concept, especially useful for those who believe that punitive action is the only response to an unintentional and non-deliberate offence.

https://www.skybrary.aero/index.php/Just_Culture
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Old 20th Jun 2021, 16:32
  #77 (permalink)  
 
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H Peacock

There are five pins. Not much excuse for not knowing something like that as it has been widely published. 😁

Seriously though, there are no excuses but there are reasons that things go wrong. Mitigating those reasons is why we fully investigate and implement corrective action instead of just pointing the finger.

There for the grace of... etc.
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Old 20th Jun 2021, 16:53
  #78 (permalink)  
 
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Exactly. I donít think the engineer(s) involved set out to do this. If it is possible to put the pin in the wrong hole, and by all accounts it can fit quite well, then itís just a matter of time if this action is taken on a regular basis. Which it is.

A bit like the 320 engine cowls: what are we up to, 45-50 incidences of them not being locked properly? Canít be anything to do with the design and/or warning systems...
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Old 20th Jun 2021, 19:35
  #79 (permalink)  
 
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PAXboy

Quite . . . the more you see the less impressive aviation safety process is . . . repeatedly, what a shambolically inept design decision, again, how many thousands of issues like this are hiding waiting to kill people I wonder . . . thankfully no plans to return to the safety lottery of aviation travel any time soon . . .
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Old 20th Jun 2021, 20:10
  #80 (permalink)  
 
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Update on the aircraft: after the nose had been raised on airbags, the gear was dropped and (presumably after inspection by the AAIB) it was judged secure enough to allow the aircraft to be towed back to the BA Base.

Photos on Twitter show, unsurprisingly, the two forward NLG doors having been ripped off but the two smaller rear doors appear to be more-or-less intact.
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