----- Forwarded by Guy
Exon/OAS/OS/DOI on 02/18/2003 10:54 AM -----
To:
Jim_Bredy@fws.gov
02/18/2003 10:51 AM
Subject: N737 Wing Skin Cracks
I inspected the P68TC OBS, S/N 400-04-OBS down in
Albuquerque last week. Two inch cracks had been discovered on the bottom
skin of the inboard leading edge. They were located outboard near the engine
nacelle. Closer inspection and removal of the skin revealed the outboard rib
cracked and broken where it attaches to the main spar. The middle rib also
had cracks starting between the two rivet holes that fasten it to the spar.
Cracks were also observed in the upper firewall near the engine mounts and
edges. This damage was identical on both left and right wings.
The outboard portion of the inner leading edge helps
support the engine cowling. On the left engine the outer rib supports the
induction filter and alt air box assy. The right engine airbox assembly is
mounted on the inboard rib of the outboard leading edge. No cracks were
found on the outboard leading edge assy.
I do not suspect these cracks are related to an
overstress situation. I also do not feel the weight of the filter assy. is
the source since they appear on the right side without the filter assembly
as well. Long term fatigue (5200 hrs A/C TT) operating in low level
environment or engine vibrations could be contributors. The firewall is not
structural and although I would not consider them directly related, probably
developed for the same reasons.
The damage was discovered at a point of being minor
although the repair requires the leading edge being replace as an assembly.
See the attached photo's showing the cracks.
