Extruded Shim

[verymadmac]

I have an aircraft which has had part of a tapered shim, extrude out from under a fitting.
It appears to be just the corner of the shim so support has only been lost under one end fastener.

While replacement of the shim is desirable , the aircraft is only 600 hours from C check. It appears very frequent inspections (every 10 hours)of the fitting looking for shim movement, cracking, leaks, etc may allow its continuation in service until the C check.

So my question i, is this a typical approach for this type of issue?

 

[SWComposites]

How do you know for certain that only one fastener is affected?
How do you know that fastener clamp-up is not lost on all fasteners attaching the fitting?
How will you inspect the fasteners for fatigue cracking?
Are there any hidden plates (sandwiched between two other plates) in the joint which cannot be inspected?
What specific parts are attached by the affected fasteners?
What does the SRM state for this condition?

 

[SAITAETGrad]

Generally, one would need a better understanding of the situation to pass judgement. Are you sure you won't end up with vibration or other structural issues as a result. There have been a number of accidents like this one:

http://en.wikipedia.org/wiki/Partnair_Flight_394

Inspections are generally done to find damage, not to track damage growth. Your proposed daily inspection is suspect at best.

 

[thruthefence]

If I may segue slightly off topic, can some of you structural guys comment on this, from the wiki link on Flight 394?

"Partnair said that an F-16 fighter jet was flying at a faster velocity and closer to the Convair than reported in the media. Therefore the jet, which would have broken the supersonic barrier at that point, would have had flown too close and at supersonic speed near the Partnair plane. The pressure wave, resulting from the breaking of the supersonic barrier, would have caused the Convair to disintegrate in midair.[2] Flygtekniska Försöksanstalten, a Swedish aviation technology research facility said that there was a 60% chance of this being the cause."

"disintegrate in midair"?

 

[rb1957]

well it was a connie ... probably old enough to collect old age benefit ! still a complement to the design.

but to the question posed ... could a SS shock disintegrate an airplane ? yes (pert near anything can happen), probability in my mind more like 1e-7 ... it'd have to be Very close !

 

[WKTaylor]

Thru the fence... as I remembered: Counterfeit bolts [attaching the V Stab to the fuselage] were blamed for this mishap.

"...As the aircraft neared the Danish coastline, 22,000 feet (6,706 m) over the North Sea, the tail section of the aircraft started to rattle.[2] The broken APU mount vibrated due to counterfeit bolts in the tail of the aircraft, which were weaker than the authentic parts. The investigators concluded that the vibrations reached the same frequency and went into synchronization, a phenomenon known as resonance, causing a coupled harmonics force similar to the one that caused the Tacoma Narrows Bridge collapse in 1940; the force of each vibration wave would add to that of another vibration, increasing in amplitude until the structure failed.[2]

With a rising level of vibration, a failure in the plane's tail section must have become evident to the crew. In the investigation, it was found that the crew triggered the fire extinguisher for the APU.[3] The rudder oscillated to its maximum limits and jammed to the left,[3] and the aircraft was forced into an abrupt left turn that caused the aircraft to roll over. The crew recovered for a brief moment. The rudder jammed to the left again and the shroud doors, which provide mechanics access to weights in the aircraft's tail that control the movement of the rudder, broke off. The aircraft went into a second roll, and the tail section of the aircraft disintegrated. The rest of the aircraft disintegrated on the way down to the sea.[2]..."



Regards, Wil Taylor

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