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I was reading this question related to the parts suffering the most G forces. Reflecting about that question I question myself about hard landing, which is not a normal operation.

So, my especific question is: when an airplane is suffering a hard landing event, which are the structural parts (and any other part that might not be structural and I might be forgetting) that are suffering the main damages and why?

Will this answer depend on the airplane vibration mode (i.e. location of engine masses)?

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here are the main parts at risk for structural integrity after a hard landing:

the landing gear itself and the attachment points of the gear to the fuselage and/or wings

the fuselage-to-wing attachment structures

the engine-to-wing (pylon) or engine-to-fuselage attachment structures

the main fuselage structure in the immediate vicinity of the wing attachment points

If the hard landing involves a tail strike, then the integrity of the aft pressure bulkhead is at risk.

Note that the structural integrity risk is not simply one of prompt failure due to an overstress impulse load, but also subsequent premature fatigue failure arising from microcracks caused by the hard landing stresses- especially if that cracking occurs in a location which is inaccessible for inspection.

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I believe it could be implied with niels nielson’s answer, but do not neglect inspection (and torque) of fasteners.

In my limited experience, all structures and gear can appear undamaged and normal but the fasteners (e.g., of the gear, engine mounts, wing attachments, etc.) may be stretched, bent, or deformed as would be evident only by torque checks and very close inspection, even removal.

Replace all suspect fasteners and kindly resist the temptation to simply retorque them. I know of no specific criteria but anything more than a 1/4 turn to retorque to meet spec would raise my eyebrows and require more inspection and/or replacement. (And of course this would be done by only those legally authorized to make the particular aircraft’s inspections and repairs.)

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