Structural failure due to harmonic vibration

Big John wrote:

Jay

After the two crashes they found the problem and fixed it but then
they didn't sell good to airlines due to crash history.

Navy bought a large number (with MAD gear) after fix, that are now
configured to the P-3C Orion (ASW) configuration and many P-3's were
sold around the world in ASW confguration. Navy is still using them
while waiting for a new bird. There is a request out to industry for a
new bird???

That was a different airplane, and a different problem. The one Jay is
referring to were the orignal Electras, similar to what Amelia Earhart
flew. The Northwest flight was an L-14 Super Electra, a larger, more
powerful version of Amelia's L-10E.

http://en.wikipedia.org/wiki/Northwe...lines_Flight_2

What you are describing are the L-188 accidents in 1959/60. The were a
result of what was called the "whirl mode" failure.

The aircraft would perhaps have a hard landing, which would weaken or
break one of the struts in an engine mount. The engine would then be
able to move around slightly on the remaining mounts. When the aircraft
subsequently encountered moderate turbulence, the mounts would not be
able to restrain the engine from acting like a gyroscope, resulting in
the hub of the prop rotating in a circle. In one of the accidents, it
looked like the engine had moved up to 35 degrees out of line.

Unfortunately, when the crew reduced engine power because of the onset of
whirl mode, the frequency of the whirl mode would reduce, and eventually
would match that of the wing. The sympathetic vibration would grow in
magnitude until the wing structure failed.