Structural Failure

Here is the AAIB report for the Neil Williams accident referenced by Mark_1

https://assets.digital.cabinet-office.gov.uk/media/5422fa24e5274a1314000757/15-1971_G-AWAR.pdf

mmgreve wrote:

I’d love for the pilot to have a chat with the Danish F16 pilot who bailed out last year, due to a gear failure.

What are you implying? That the value of a plane is higher than the value of a pilot’s life?

the military have SOPs as well. I Suspect that, possibly in consultation with engineering, that particular one ended in “point aircraft somewhere empty, then eject”. Predictable scenarios like this are played through on the ground so safety-of-life decisions are not made up at the spur of the moment.

It’s not possible to gear-up land planes at say 140kt (the rough Vs of an F16 in ground effect) and be sure of walking away, and that’s on a runway.

This is why certified SE aircraft have a max Vs of 60kt (65 in a few cases) – so they can be force landed in a field. Uncertified types don’t have this limit so if you have a homebuilt whose “realistic” Vs is say 80kt, an engine failure is likely to be interesting, especially with the reduced structures normally used.

I have learned to not worry about structural failure of the “loss of a whole wing” nature in certified aircraft. Yes, it has happened, but seemingly most often during truly abusive piloting. I do recall an alarming video of a Partenavia twin losing a wing – because the pilot deliberately looped it! I am very much more worried about me failing the plane, than the plane failing me! I fail the plane, if I press it into rough air, or maneuvering faster than Va. Be mindful that certified GA planes meet the minimum requirement of 3.8G and thereafter, a 1.5 factor of safety. That means that at a G greater than 3.8, you might bend it, but it will remain flyable after sustaining loads as great as 5.7G. for most pilots, 5.7 G is greying out territory. Slower than Va, you’re just not going to get to 5.7G, so you’re not going to render the plane completely unflyable. Though beyond 3.8G (if you can get the plane there), you could bend something, which should definitely be worrisome!

Think about it, if you were to deliberately try to bend the plane in flight, how would you go about doing it? For my experience, a pilot will be too afraid to pull enough G to bend a plane, though they may overspeed it – that is more worrying to me! Overspeeding can get you close to flutter (Leeward’s Mustang at Reno). Flutter won’t take a wing off, but you might loose an important part, or trim. I have declined to test fly several aircraft, until what I determined to be too loose a flight control or trim tab was rectified.

I have never worried about bending a plane in flight, or a major structural part leaving. Honour the plane, it will honour you!

@Pilot_DAR, you’re right, it is very rare to have a structural failure assuming the plane was at full health to begin with, unless you’re being very abusive.

There are a couple of cases of structural failures in flight, following previous damage to the wing – I recall one where the pilot had hit a bale of hay on the previous landing and thought it was probably OK to fly again. THAT is really scary, especially if you’re renting or otherwise sharing the plane with a broader group.

Wasn’t that a Robin in France, where somebody hit the bale of hay and the next renter had the wing come off?

The problem with this kind of stuff is that the club “will” get the wing inspected but you never know how well that was done. Clubs/schools have a big incentive to do the minimum possible. I once had a door lock on a PA28 jam; it unjammed later and we got out OK. The school claimed that an engineer looked at it and found nothing wrong. Later I discovered they lied; it was never looked at. The issue was intermittent.

I peripherally know of one case where a similar thing happened, also in France. The club had the thing “inspected” and the “engineer” found nothing wrong. I fairly strongly suggested to the pilot who used to rent it that he flies another plane And sure enough after some weeks or months a crack opened up on the outside… last I heard, the plane was grounded. I think that one was a wooden-wing plane, though not a Robin.

I peripherally know of one case where a similar thing happened, also in France. The club had the thing “inspected” and the “engineer” found nothing wrong. I fairly strongly suggested to the pilot who used to rent it that he flies another plane And sure enough after some weeks or months a crack opened up on the outside… last I heard, the plane was grounded. I think that one was a wooden plane, though not a Robin.

I “peripherally heard about that one”, too, Peter, and although one should always be careful about posting hearsay on forums, the club involved apparently put that aircraft – a tatty old Jodel – back into service again after the second incident, after thorough inspection of course (one hopes so, anyway).

Peter wrote:

Wasn’t that a Robin in France, where somebody hit the bale of hay and the next renter had the wing come off?

Someone I know many many years ago while a student pilot put the wingtip of a Taylorcraft into a post at taxi speed. The torque at the wing root is tremendous even from a low speed, and it caused a compression fracture in the rear wooden spar.

We had someone at our club in Houston strike a Cessna 170 wingtip against a hangar at taxi speed. That buckled the rear spar (metal). Tagging a wingtip on something even if there’s no apparent damage or just a small dent in the leading edge I think requires a very close inspection of that wing’s structure.

Apropos of this thread, although the cause is different to what we’re discussing:

NTSB report

Note that whatever he did not only tore the outboard wings off, but the empennage too and the prop hit the remaining part of the wing that was still attached to the fuselage while still in the air, so the engine was torn off too.