NTSB Identification: LAX86MA268.
The docket is stored on NTSB microfiche number 33874.
Accident occurred Wednesday, June 18, 1986 in GALVESTON, TX
Probable Cause Approval Date: 05/27/1988
Aircraft: AEROSPATIALE AS-355F-1, registration: N5796T
Injuries: 1 Uninjured.

NTSB investigators traveled in support of this investigation and used data obtained from various sources to prepare this aircraft accident report.

THE PLT RPRTD THAT WHILE APCHG AN OIL DRILLING PLATFORM FOR A LNDG, HE OBSERVED THE MAIN ROTOR BLADES GO OUT OF TRACK ABOUT 8 TO 10 INCHES. HE ALSO RPRTD THE HELICOPTER DEVELOPED A 1:1 VERTICAL VIBRATION. DRG THE LNDG, THE HELICOPTER ENTERED INTO GROUND RESONANCE & THE PLT IMMEDIATELY SHUT DOWN BOTH ENGINES. AN EXAM OF THE HELICOPTER REVEALED THE LEFT FORWARD TRANSMISSION SUPPORT BAR (TSB) WAS BUCKLED & CRACKED AT MIDSPAN. A METALLURGICAL EXAM OF THE FRACTURE AREA ON THE TSB REVEALED EXTENSIVE, LOW CYCLE, HIGH AMPLITUDE, FATIGUE CRACKING. THERE WAS EVIDENCE THAT THE PROPAGATION TIME OFTHE FATIGUE OCCURRED OVR ABOUT 5 HRS OF OPN. THE INV DID NOT REVEAL WHEN THE ORIGINAL BUCKLING OF THE TSB OCCURRED. NO HISTORY OF A PREV HARD LNDG OR GND REASONANCE WAS FND. ALSO, THE RED ARM OF THE STARFLEX HAD FAILED; AN EXAM INDCD IT HAD RUPTURED EITHER UNDER STATIC LOADS, OR VERY RAPIDLY UNDER HI DYNAMIC LOADS. WHEN TESTED, EXTN & RETRACTION TIMES OF LNDG GEAR DAMPERS WERE 8.34 TO 10.38 SEC; AFTER ACDNT, TIME LMTS ESTABLISHED AT 6 TO 13 SEC, PREVIOUSLY 11.1 TO 13.1 SEC

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

REASON FOR OCCURRENCE UNDETERMINED




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