NTSB Identification: CHI88FA110.
The docket is stored on NTSB microfiche number 40016.
Scheduled 14 CFR operation of BRITISH AIRWAYS (D.B.A. operation of BRITISH AIRWAYS )
Accident occurred Monday, May 09, 1988 in CHICAGO, IL
Probable Cause Approval Date: 06/25/1990
Aircraft: BOEING 747-136, registration: GAWND
Injuries: 304 Uninjured.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

THE ACFT WAS ON FINAL APPROACH TO CHICAGO O'HARE INTER'L AIRPORT WHEN A STRUCTURAL FAILURE OF THE NUMBER THREE FLAP TRACK OCCURRED. THE ACFT SUSTAINED SUBSTANTIAL DAMAGE TO THE LEFT WING, LEFT INBOARD FLAP ASSEMBLY, LEFT INBOARD SPOILERS AND SPOILER SUPPORT BEAM. THE PILOT EXPERIENCED SIGNIFICANT UNCOMMANDED ROLL AND YAW, BUT REGAINED CONTROL OF THE ACFT AND EXECUTED AN UNEVENTFUL LANDING. THE INVESTIGATION HAS REVEALED A HISTORY OF FLAP TRACK CRACKING PROBLEMS ASSOCIATED WITH STRESS CORROSION AND DESIGN INADEQUACY. A DESIGN CHANGE OF THE MEMBER WAS ACCOMPLISHED IN 1971 BY THE MANUFACTURER, BUT FLAP TRACKS OF THE EARLIER DESIGN WERE ALLOWED TO REMAIN IN SERVICE ON 239 AIRCRAFT. THE AIRWORTHINESS DIRECTIVES AND SERVICE BULLETINS APPLICABLE TO THIS PARTICULAR STRUCTURAL MEMBER ARE NOT ADEQUATE IN METHODOLOGY AND PERIODICITY TO ENSURE CRACK DETECTION, AND DO NOT REQUIRE INSPECTION FOR THE CAUSE OF THE CRACK-CORROSION PITS.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

FAILURE OF THE NUMBER THREE FLAP TRACK DUE TO STRESS CORROSION CRACKING. FACTORS CONTRIBUTING TO THIS FAILURE ARE INSUFFICIENT DESIGN OF THE MEMBER AND INADEQUATE INSPECTION AND MAINTENANCE PROCEDURES TO DETECT CRACKS BEFORE THEY PROPAGATE TO A CRITICAL LENGTH.

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