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Since it's certain that debris deflectors would have stopped the piece of tyre that punctured Concorde's fuel tanks in the fateful Air France 4590 disaster and caused an explosion, why are they not installed on most modern aircraft? They could prevent a similar incident in the event of a tyre explosion or other, even harder metallic debris that can be tossed/deflected onto the fuel tanks by the tyres spinning or the wheels.

Wouldn't this modification have saved the Concorde? Cost of maintenance aside, should it not be a requirement on all aircraft? Do they leave it off for aesthetic reasons?

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securitydude5
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    Debris deflectors are there to stop debris that's been kicked up from the wheel. Stopping the parts of an exploded tyre would be a much harder job, so I dispute your claim that it's "certain that debris deflectors would have prevented the piece of tyre that punctured the concorde fuel tanks." Did the investigation report recommend that debris deflectors should be fitted to all aircraft? I doubt it. – David Richerby Dec 13 '16 at 11:27
  • @david-richerby If they are close to the wheel 6cm to 9cm clearence, as in truck fuel tankers covering the top front and back of the wheel, they can stop just about anything especially parts of an exploded tyre depending on the material used its thickness density and strength. Lined with tyre like rubber material, they can certainly stop exploded tyre material. – securitydude5 Dec 13 '16 at 11:40
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    Note that aircraft tyres are at much higher pressure than truck tyres (say, 200psi vs, er, well, I don't know exactly but Continental's sheet quotes load capacities for tyre pressures in the range 87-131psi). And weight is a big issue on aircraft: obviously, you could build something strong enough, but would it fly? – David Richerby Dec 13 '16 at 12:59
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    You can never really say "ignoring maintenance costs...", or "ignoring fuel costs...", or "ignoring passenger comfort..." etc. because those are exactly the factors that decide whether or not an 'improvement' is worth it. Every change is a balance between competing priorities, and weight/cost vs. safety/comfort is a 'classic' aviation dilemma. – Pondlife Dec 13 '16 at 14:21
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    "Do they leave it off for aesthetic reasons?" Please. Don't be ridiculous. – David Richerby Dec 13 '16 at 15:22
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    The tire debris did not puncture the tank; the debris caused a tank overpressure and rupture from the inside outward. – J W Dec 13 '16 at 17:28

5 Answers5

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If you look at the current regulations for aircraft certification, at least half the rules can be traced back to a specific incidence. Why would aviation-grade hydraulic fluid be required to be non-flammable? Because of this Caravelle crash. And so on.

But at some point even the bureaucrats in the FAA realise that the benefits from adding the next gizmo will not outweigh the reduced performance and new failure cases of the modified airplane. In this specific case, it is better to require proper maintenance so nothing falls off an airplane in the first place, and frequent checks of the runway.

Peter Kämpf
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    To illustrate your reasoning: "G-BOAB [another Concorde] during taxiing at London Heathrow. Burst of tyre No 2 leading to damage to the water deflector. Tank 1 suffered minor penetration, probably from a piece of the deflector". This is from F-BTSC accident BEA report. – mins Dec 14 '16 at 10:20
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Debris deflectors would not have worked for Concorde and certainly aren't universally viable, unless they were somehow designed to magically deflect all debris coming from all angles at all speeds away from any part of the airframe. That's not going to happen.

What we have here is a freak accident happening due to a combination of freak coincidences. Such a thing can never be prevented from happening. You could stay at home always so you can't get killed in a traffic accident, but you'd still be potentially killed by an asteroid hitting your home (yes, it's happened).

Same with aircraft and FOD. You can try to reduce the risk, but never completely eliminate it. FOD patrols on airports are a good way, far better than technology that adds weight to the aircraft that works in some highly specific scenarios only.

jwenting
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    I would hardly call the Concorde accident a freak accident; it was the result of a collection of errors of gross negligence and disregard for maintenance procedures and operating limitations. The debris on the runway was just the final catalyst that brought all elements together to lead to the flight's demise. – J W Dec 13 '16 at 17:30
  • @JonathanWalters that debris being there was a freak accident. – jwenting Dec 13 '16 at 21:17
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    But you describe a bunch of things as "freak coincidences" that @JonathanWalters refers to as "gross negligence and disregard". That's quite a difference. – David Richerby Dec 14 '16 at 01:43
  • @DavidRicherby "gross negligence and disregard" is just lawyer speak for "we want someone to blame so we can sue them for something that nobody could predict" – jwenting Dec 14 '16 at 08:06
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    @jwenting Errrr, no. Gross negligence is lawyer speak for "you did your job so badly and dangerously that any idiot on the street could see that something catastrophic was going to happen." It's pretty much the exact opposite of what you claim it means. – David Richerby Dec 14 '16 at 09:24
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Sections 4.2 and 4.3 of the Accident Report set out recommendations based on the investigators findings. Implementation of these recommendations would prevent such an accident.

The recommendations did not include landing-gear debris-deflectors.

Since it's certain that debris deflectors would have stopped the piece of tyre that punctured Concorde's fuel tanks

It might seem plausible but it is not certain.

See 1.6.2.4 Deflectors - a different type of deflector but an illustration that deflectors may also contribute to accidents - if the debris is large enough.

You can only be certain of the effectiveness of debris deflectors by actually testing with the relevant landing gear and identical debris at high speed. In particular you would need to test whether a debris deflector could catch a 43 cm curved metallic strip and the entire energy of a disintegrating tyre in the main landing gear rotating at very high speed. In the absence of such testing, we cannot be certain.

RedGrittyBrick
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  • and of course, if it can catch that specific thing, there's no way to know it won't make having something else on the runway (say a 30cm triangular piece) worse... – jwenting Dec 14 '16 at 08:07
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Putting arcane equipment on every single commercial aircraft to (hopefully) prevent a 1-in-a-billion accident is not a good idea.

Did you consider that when you add weird new equipment to a lot of aircraft that it can cause an accident? Did you know the FAA used to require every pilot to undergo real spin training... until they found out more pilots were getting killed in spin training than were getting killed in real spins.

Tyler Durden
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    What's "arcane" or "weird" about a debris deflector? – David Richerby Dec 14 '16 at 01:44
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    @DavidRicherby it is not a normal feature on an aircraft, or at least not on any aircraft I have ever flew, including commercial jets. The only place I have ever seen them (and only in pictures, not real life) is on military jets nose wheels that are flying out of dirt airstrips. I have never seen them on any aircraft on the main wheels ever. – Tyler Durden Dec 14 '16 at 02:38
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    There's a lot of room between "not a normal feature" and "arcane" or "weird". Boeing's unpaved strip kit for the 737 included nose wheel and main gear debris deflectors, as well as other modifications. You've probably never seen these things because you're not in an area where gravel runways are common (me either). – David Richerby Dec 14 '16 at 09:50
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Since I cannot comment on any of the answers, I will just add an answer myself. There seems to be a misunderstanding of the accident. It wasn't a piece of tire that ruptured the fuel tank. Also it wasn't negligence that caused the plane to crash.

It was a piece of aluminium that was attached as a repair measure on a boeing that happened to come off and ended up on the runway. As far as negligence goes.... it was not detected, since the runway is NOT checked after every take-off, and the piece of aluminium happened to be from th plane taking off right before the concorde. Just bad luck... :(

Whacko
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  • You could say it's negligence from that boeing repair team :) – Antzi Feb 21 '17 at 09:39
  • while this addresses a misunderstanding behind the question, it does not answer the main question, that is valid despite the misunderstanding. – Federico Feb 21 '17 at 09:39
  • additionally, the misunderstanding was already addressed in the comments to the original question. – Federico Feb 21 '17 at 10:05