Sat, Feb 19, 2005
AD NUMBER: PL2005-04-51
MANUFACTURER: Boeing
SUBJECT: Airworthiness Directive
PL2005-04-51
SUMMARY: On May 7, 1991, we issued AD 91-11-01,
amendment 39-6887 (56 FR 22306, May 15, 1991), for certain Boeing
Model 747 series airplanes. That AD requires repetitive inspections
for cracks of the frame structure and skin in the fuselage section
41, and repair if necessary. That AD also provides for an optional
terminating action for the repetitive inspections. That AD was
prompted by recommendations of the FAA-sponsored Boeing Model 747
Structures Working Group. We issued that AD to prevent sudden
decompression of the fuselage. Since the issuance of AD 91-11-01,
we have received several reports of large fatigue cracks common to
fuselage frames in the upper deck area on Boeing Model 747-200C,
-200F, and -300 series airplanes. Most of these airplanes had been
inspected in accordance with AD 91-11-01. Many fatigue cracks
occurred near stringers S-10 and S-10A, but other cracks were also
reported. The cracking is due to cyclic pressurization of the
airplanes. We also have received two recent reports of severed or
nearly severed adjacent frames at body station (BS) 420 and BS 440
near stringer S-10A on Boeing Model 747-300 series airplanes. Both
airplanes had been inspected in accordance with AD 91-11-01. In
both reports, missing fasteners common to the skin at frame shear
tie flanges were detected in the vicinity of cracks. In one case,
eight fasteners were missing from the body skin at the severed
frame at BS 440. One airplane had accumulated 11,641 total flight
cycles; the other airplane had accumulated 11,880 total flight
cycles. In light of these reports, we have determined that, for
certain Boeing Model 747-100B SUD, -200C, -200F, and -300 series
airplanes; and certain Boeing Model 747-200B series airplanes
retrofitted with a SUD; the inspections required by AD 91-11-01 do
not adequately detect fatigue cracks at BS 420, 440, and 460
between stringers S-8 and S-12 inclusive. Such fatigue cracking, if
not detected and corrected in a timely manner, could lead to
severed frames, and consequent rapid decompression and loss of the
structural integrity of the airplane.
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