Serious incident MBB BK-117 A4 N528SF,
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ASN Wikibase Occurrence # 370435
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Date:Monday 26 August 2002
Time:21:35 LT
Type:Silhouette image of generic BK17 model; specific model in this crash may look slightly different    
MBB BK-117 A4
Owner/operator:Rocky Mountain Helicopters
Registration: N528SF
MSN: 7104
Year of manufacture:1986
Engine model:Lycoming LTS-101-650
Fatalities:Fatalities: 0 / Occupants: 5
Aircraft damage: Minor
Category:Serious incident
Location:Bradenton, FL -   United States of America
Phase: En route
Departure airport:Naples, FL
Destination airport:St. Petersburg, FL
Investigating agency: NTSB
Confidence Rating: Accident investigation report completed and information captured
The pilot said that while in cruise flight at an altitude of 1,000 feet, a speed of about 130 knots, and about 60 percent torque, without warning he heard a loud explosion from the right side of the helicopter, with simultaneous No. 2 engine fire and failure warning lights and indications, along with severe vibrations. He said that the helicopter yawed several times from left to right and he heard a "whopping" sound. He also said that at the same time the No. 1 engine torque meter needle moving rapidly from about the 9 to 3 or 4 o'clock positions on the gauge. The investigation revealed two of the power turbine blades and four rear bearing support housing (RBSH) failed in overload. The hub had been displaced from the engine centerline, and a deflection had occurred at the engine case axial midpoint, along with a misalignment of the inlet housing and the rear bearing support housing (RBSH). The resultant damage to the gas producer (GP) system, was consistent with an assembly error and mechanical failure having occurred by the loss of critical internal operating clearances and radial support for the rotors. Continued engine operation as the failure progressed led to compressor surge and the emergence of combustion gases from the No. 2 engine inlet, which ignited inlet cowling material. The No. 1 engine ingested smoke and combustion by-products from the engine cowling fire which caused a temporary stall condition.

Probable Cause: Improper maintenance/installation of the No. 2 engine power turbine (PT) wheel assembly by company maintenance personnel, which resulted in deflection at the engine case axial midpoint and misalignment between the inlet housing and the rear bearing support housing (RBSH) which resulted in damage to the engine and an in-flight fire.

Accident investigation:
Investigating agency: NTSB
Report number: MIA02IA160
Status: Investigation completed
Duration: 2 years and 5 months
Download report: Final report




Revision history:

25-Mar-2024 10:41 ASN Update Bot Added

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