Accident Aerospatiale AS-355F-1 N5796T, Wednesday 18 June 1986

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Date:	Wednesday 18 June 1986
Time:	09:55 LT
Type:	Aerospatiale AS-355F-1
Owner/operator:	Petroleum Helicopters, Inc.
Registration:	N5796T
MSN:	5166
Total airframe hrs:	3500 hours
Engine model:	Allison 250-C20F
Fatalities:	Fatalities: 0 / Occupants: 1
Other fatalities:	0
Aircraft damage:	Substantial
Category:	Accident
Location:	Galveston, TX - United States of America
Phase:	Approach
Nature:	Ferry/positioning
Departure airport:	High Island 571, TX
Destination airport:
Investigating agency:	NTSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
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

Probable Cause:

Accident investigation: