A Fokker 27 loses it's propeller at take-off in Paris (CDG)

[tdracer]

Barkingmad, several years ago I was involved in a high speed turboprop, using those highly swept 'banana' blades (no, not the 7J7, this one actually had a flying prototype).

At any rate, we were told to treat anything that could cause a blade failure as catastrophic (i.e. less than 10-9/hr probability). Reason was that if a blade failed at power, the resultant imbalance and vibration would structurally fail the wing

I know very little about the F27 (ah, I did fly on an F28 a few times, does that count? ) But looking at some of the photos of what remained of the gearbox, it makes me wonder if it wasn't designed to fail. That is, if it lost a prop blade, I wonder if the gearbox was designed to fail and let the prop separate from the engine to protect the wing structure from the vibrations.

[lomapaseo]

I wonder if the gearbox was designed to fail and let the prop separate from the engine to protect the wing structure from the vibrations

Typically a rule in one section of the regs (part 25 etc.) can not specify a requirement in another section (part 33 etc.). They need be stand alone as if the engine and/or prop was to be installed on another type plane.

However the loads generated by a prop separation need be considered when the wing is designed.

Now between the engine gearbox and the prop, the idea is to not create an unsafe failure condition at the engine level greater than the prop failure, like comming off its mounts. Seeing as none of these extra bad things happened, it was a sucess.

[Lord Lucan]

Difference to damage if pressurised

This prop failure occurred soon after take-off. I am curious to know whether the damage to the fuselage would have been significantly greater had the aircraft been fully pressurised at the time of the failure. (a bit over 4psi differential pressure for the F27).

Anyone out there with some knowledge of structures care to comment?

[Yankee Whisky]

Prop vs gearbox failure ?

Many of you are writing about propeller failure etc. When I look at the pictures, the whole bloody gearbox departed with the props. Does that make it a propeller blade failure or a gearbox failure ? Please let the official investigation determine cause, OK?

[DaveReidUK]

When I look at the pictures, the whole bloody gearbox departed with the props

Had the gearbox departed initially, with an intact prop which had then struck the fuselage, I suspect that we would be looking at a rather larger hole in the fuselage, if not complete structural failure.

[Machinbird]

Originally Posted by Yankee Whisky

Many of you are writing about propeller failure etc. When I look at the pictures, the whole bloody gearbox departed with the props. Does that make it a propeller blade failure or a gearbox failure ? Please let the official investigation determine cause, OK?

Yankee Whisky,

For one who knows how to read the tea leaves, it is an obvious failure originating at a flaw at the blade root. The stop marks are very visible in BEA's picture of the failed hub.

The blade left first. The question then is, why did it get that far?

[Yankee Whisky]

For one who knows how to read the tea leaves, it is an obvious failure originating at a flaw at the blade root. The stop marks are very visible in BEA's picture of the failed hub.

The blade left first. The question then is, why did it get that far?
Be that as it may, the real question is "which came first; the chicken or the egg ?" Did the gearbox fail causing high gyroscopic loads on the prop disc causing one blade to fail or did the blade root fail first causing imbalance to crack the gearbox ?

[lomapaseo]

Did the gearbox fail causing high gyroscopic loads on the prop disc causing one blade to fail

I believe that any gyro loads have to react at the center of rotation with the gearbox firmly attached as ground. About the only way you can transfer these loads into the blade would be if a large mass like the aircraft itself should alter the axis at a high rate and react the load through the gearbox to the blades.

In that case all blades would be severely distressed in a similar fashion. I'm betting the aircraft tail would never survive such pitch or yaw loads.

By now the investigation should have pin pointed the exact location of the fracture initiation and the time it took to progress to fracture as well as the frequency of the cyclic loading, arrest marks etc.