NTSB Identification: MIA99LA220.
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Nonscheduled 14 CFR operation of FEDERAL EXPRESS CORPORATION (D.B.A. FEDERAL EXPRESS )
Accident occurred Saturday, August 07, 1999 in MEMPHIS, TN
Probable Cause Approval Date: 05/17/2001
Aircraft: McDonnell Douglas DC-10-10F, registration: N68058
Injuries: 5 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
While on final approach with full flaps selected and indicated, the left inboard trailing edge flap and vane separated. The autopilot was disconnected and approximately 1/2 right aileron input was needed to counter the left banking tendency. The landing was reported to be firm but with less 'controllability'. Structural damage occurred to the left side of the fuselage due to flap and/or vane contact. The four H-11 type bolts of the forward attach point of the outboard hinge of the left inboard trailing edge flap failed due to stress corrosion cracking. Chromium was detected in the fracture origin of bolts Nos. 1-3; no determination was made as to why chromium was present. The two H-11 type bolts of the aft attach point of the outboard hinge of the left inboard trailing edge flap failed due to ductile overload. No material or processing discrepancies were found. H-11 bolts are susceptible to stress corrosion cracking. The FDR readout indicated that the maximum left roll was 8.09 degrees and flap extension speed was exceeded on landing No. 1 for approximately 13 seconds when the flaps were extending from 16 to 20 degrees. No flap overspeed protection is afforded in that range.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The inadequate design by the airplane manufacturer for using bolts to secure the inboard trailing edge flap that are susceptible to stress corrosion cracking. Also, the stress corrosion cracking failure of the four H-11 bolts that secure the left inboard trailing edge flap to the outboard hinge which allowed the separation of the flap and vane while on final approach. Full narrative available
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