Boeing 747 Fuselage Cracks Prompt FAA To Issue Emergency AD

Air Safety Week, March 7, 2005

The Federal Aviation Administration (FAA) issued Emergency airworthiness directive (AD) 2005-04-51 on Feb.17. Model 747-100B SUD, -200C, - 200F, and -300 series airplanes; and certain Boeing Model 747-200B series airplanes retrofitted with a stretched upper deck (SUD) are affected.

This AD was prompted by reports of large cracks common to fuselage frames in the upper deck area. FAA issued this AD to detect and correct fatigue cracks in the frames and body skin at body stations (BS) 420, 440, and 460 between stringers S-8 and S-12 inclusive, which could lead to severed frames, and consequent rapid decompression and loss of the structural integrity of the airplane.

ASW Comment: This inspection & repair program will probably hasten the laying up of many older Classic 747's. The Taiwan Report on the crash of China Airlines elderly 747 flt CI-611 in the Taiwan Straits will be available shortly.

The Issue In Perspective

On May 7, 1991, FAA 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. FAA issued that AD to prevent sudden decompression of the fuselage.

Since the issuance of AD 91-11-01, the FAA has 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.

FAA has also 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.

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