ASN Wikibase Occurrence # 235266
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| Date: | Wednesday 19 August 2015 |
| Time: | 19:15 |
| Type: |  Sikorsky S-61A |
| Owner/operator: | Croman Corp |
| Registration: | N1043T |
| MSN: | 61083 |
| Year of manufacture: | 1982 |
| Total airframe hrs: | 40309 hours |
| Engine model: | GE T58-GE-402 |
| Fatalities: | Fatalities: 0 / Occupants: 2 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Ironside, OR -
 United States of America
|
| Phase: | Manoeuvring (airshow, firefighting, ag.ops.) |
| Nature: | Fire fighting |
| Departure airport: | Baker City, OR (BKE) |
| Baker City, OR (BKE) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The commercial pilot reported that they had picked up 4,000 lbs of water from a pond for a helicopter firefighting operation and were starting a climbing left turn. About 20 ft above the ground, the No. 2 (right) engine lost power, and the rpm dropped. The pilot dumped the water from the bucket and attempted to gain airspeed and altitude as the helicopter entered a small valley. The pilot also attempted to release the longline and bucket to no avail. The second pilot used the emergency throttle, but the helicopter continued to lose engine and rotor rpm. Unable to gain altitude and with the terrain rising, the pilot landed the helicopter, which subsequently rolled over and came to rest on its right side. Before touchdown, the longline and bucket had impacted brush and trees and the bucket became entangled in a fence, which likely hindered the pilot's ability to successfully land the helicopter.
On-scene examination revealed that the fuselage belly hook released the longline as intended; however, one of the two hydraulic quick-disconnect couplings failed to release the longline. A safety wire was used to connect the fitting on the quick-disconnect mechanism to the coupling. The use of the safety wire did not allow the quick-disconnect mechanism to function as intended and release the longline.
The examination of the No. 2 (right) engine revealed metallic debris on all four magnetic plugs. The front frame accessory drive was manually rotated, and no concurrent rotation of the centrifugal fuel purifier drive splines was observed. Removal of the radial driveshaft revealed scallop-shaped wear marks around the shaft, which matched the mating female splines of the pinion assembly. In addition, about 0.10 inch of material wear was observed on the front frame housing consistent with pinion gear assembly contact. Removal of the pinion gear assembly from the accessory gearbox revealed that the pinion gear, which mates with the bevel gear, exhibited wear on the gear teeth and some metal smearing along the tips, which is consistent with gear disengagement. When the bevel and pinion splines disengaged, the fuel and oil pumps were no longer being driven, so fuel and lubrication to the engine were cut and the engine lost power.
Disassembly of the pinion support assembly revealed roller ball, bearing cage, and race damage to the upper support bearing and wear to the bevel gear teeth consistent with that observed on the mating pinion. Aluminum oxide particles were embedded in the cage pocket and inner races of both bearings and likely contributed to the bearing wear that eventually caused bevel and pinion gear disengagement.
According to the manufacturer, aluminum oxide is not present in this engine's bearing or any component within the oil lubrication system pathway. However, aluminum oxide can be introduced into the engine during the overhaul/repair process if measures are not taken to maintain a clean environment, including management of air flow when bearings are exposed. Aluminum oxide is abrasive and, once embedded into the bearing, will typically result in uneven wear and accelerated failure. The last engine light overhaul was completed about 1 year before the accident, and it is likely that the aluminum oxide was introduced at that time.
Probable Cause: A loss of power to the No. 2 engine due to the failure of the accessory gearbox drivetrain. Also causal was the pilot’s inability to release the external longline due to the use of a safety wire across the coupling of the quick-disconnect mechanism, which interfered with his efforts to land. Contributing to the accident was the repair facility’s failure to maintain a clean environment, which resulted in the inadvertent introduction of a contaminant during the engine overhaul/repair process.
Accident investigation:
 |
|
Sources:
NTSB
http://aerossurance.com/helicopters/maintenance-errors-fire-s61a/
Location
Media:
An engine power loss due to contamination in the overhaul shop and wire locking left on a quick release mechanism conspired in this fire-fighting #helicopter crash.https://t.co/F6lDT4h8dJ#accident #flightsafety #aviationsafety #airworthiness #maintenance pic.twitter.com/oNDzs2IgWT
— Aerossurance (@Aerossurance) June 28, 2020
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 19-Apr-2020 17:28 | ASN Update Bot | Added |
| 28-Jun-2020 10:52 | Aerossurance | Updated [Source, Narrative] |
| 28-Jun-2020 11:00 | Aerossurance | Updated [Embed code, Narrative] |
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