ASN Wikibase Occurrence # 44178
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| Date: | Friday 17 March 2006 |
| Time: | 09:35 |
| Type: |  Kaman K-1200 K-Max |
| Owner/operator: | Grizzly Mountain Aviation Inc |
| Registration: | N263KA |
| MSN: | A940033 |
| Year of manufacture: | 2002 |
| Total airframe hrs: | 3193 hours |
| Engine model: | Honeywell T5317A-1 |
| Fatalities: | Fatalities: 1 / Occupants: 1 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Dayville, OR -
 United States of America
|
| Phase: | Manoeuvring (airshow, firefighting, ag.ops.) |
| Nature: | External load operation |
| Departure airport: | Dayville, OR |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The helicopter experienced a total loss of engine power while hovering out of ground effect during a long-line logging operation. Witnesses observed the helicopter descend vertically with the rotors visibly slowing down, nose over to an inverted position, impact the ground inverted, and roll onto its left side. Initial examination of the engine revealed that when the power turbine was rotated, the engine output adapter attached to the reduction gearbox did not rotate, indicating a mechanical disconnect within the engine. Disassembly of the engine revealed severe damage to the sun gear shaft, which coupled the power turbine to the reduction gear box. Further disassembly and materials analysis disclosed an assembly error of one of the three aft planetary gear shaft roller bearings in the reduction gear box and improper crimping of the lockcup on the N1 seal and nut assembly. These two errors resulted in misalignment in the planetary gear train leading to high tooth loading in the sun gear shaft, which resulted in stripping and separation of gear teeth and loss of transmitted torque through the reduction gear box. Examination of maintenance records indicated that the bearing assembly error occurred during an overhaul of the reduction gear box by a certified repair station 822.8 operating hours before the accident. The improper crimping of the lockcup occurred during a repair by the same certified repair station performed 350.2 operating hours before the accident.
Probable Cause: The improper overhaul of the reduction gear box assembly and improper installation of the N1 seal and nut assembly lockcup by maintenance personnel, which resulted in failure of the reduction gear box and a total loss of engine power. A contributing factor was the pilot's failure to maintain adequate rotor rpm following the power loss, which resulted in an uncontrolled descent to ground impact.
Accident investigation:
 |
|
Sources:
NTSB: https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20060327X00354&key=1
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 28-Oct-2008 00:45 | ASN archive | Added |
| 07-Aug-2010 08:35 | Alpine Flight | Updated [Time, Aircraft type, Cn, Operator, Other fatalities, Nature, Source, Damage, Narrative] |
| 21-Dec-2016 19:24 | ASN Update Bot | Updated [Time, Damage, Category, Investigating agency] |
| 05-Dec-2017 09:04 | ASN Update Bot | Updated [Cn, Operator, Other fatalities, Nature, Destination airport, Source, Narrative] |
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