ASN Wikibase Occurrence # 86890
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| Date: | Monday 16 December 2002 |
| Time: | 20:02 UTC |
| Type: |  Sikorsky S-61N Shortsky |
| Owner/operator: | Hayes Heli-Log Services |
| Registration: | C-FHHD |
| MSN: | 61490 |
| Year of manufacture: | 1971 |
| Engine model: | General Electric CT58-140-1 |
| Fatalities: | Fatalities: 0 / Occupants: 3 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Lake Errock, BC -
 Canada
|
| Phase: | En route |
| Nature: | Test |
| Departure airport: | landing area near Lake Errock |
| landing area near Lake Errock | |
| Investigating agency: | TSB |
| Confidence Rating: |  Information verified through data from accident investigation authorities |
At about 1200 Pacific standard time, the Sikorsky S-61N helicopter, C-FHHD, serial number 61490, took off from the service landing area near Lake Errock, British Columbia, with two pilots and an aircraft maintenance engineer on board to carry out performance adjustments to the engines. Two minutes later, while the helicopter was climbing through about 1000 feet above sea level (asl) at about 65 knots, the crew became aware of an intensifying whining sound which was followed by a single, loud bang. Immediately the number 1 engine lost power and the number 2 engine did not automatically compensate for the power loss.
The pilot-in-command (PIC) lowered the collective lever to enter autorotation and pushed the cyclic stick forward. Acrid smoke filled the cockpit, and flames appeared from the lower left section of the main rotor gearbox in the cabin. The PIC manoeuvred the helicopter for a southwest autorotative landing on a vacant and straight segment of Highway 7 near the Lake Errock village. During the last seconds before touchdown, the pilots saw powerlines across the road, and the PIC increased the collective to reduce the descent to avoid them. The helicopter was landed on the road at about 20 knots ground speed and the wheel brakes were applied. During the roll-out, the helicopter struck other powerlines across the road, and the main rotor blades severed a large tree on the left side of the road. The helicopter veered right and the tail rotor and tail pylon struck the same tree and broke away from the fuselage. The helicopter then started to vibrate severely, with large airframe oscillations, but it remained upright and stopped at the right-hand edge of the road. The three occupants received minor injuries, and the helicopter was substantially damaged. The in-flight fire in the cabin roof was brief and localised, and it self-extinguished.
Findings as to Causes and Contributing Factors
1.The plain bearing in the main gearbox cover for the number 1 input pinion failed, lost lubrication, and disintegrated, resulting in diverging rotational imbalance and causing the input pinion gear to overheat and weaken.
2.This rotational imbalance created bending forces that exceeded the strength of the input pinion gear causing it to fracture in overload, thereby resulting in number 1 engine overspeed and shutdown.
3.At the same time, the carbon seal for the failed plain bearing disintegrated, allowing main gearbox oil to spray onto the pinion, where the oil ignited and caused the fire at the base of the transmission.
4.Movement of the pressure regulating valve in the number 2 fuel control unit was restricted by contamination, thereby causing unstable stator vane actuator operation, engine starting difficulties, inconsistent topping settings, and unpredictable and degraded engine performance.
5.The combination of the misadjusted stator vane actuator, the fuel control unit topping settings, and a sticking pressure regulating valve prevented the number 2 engine, when number 1 engine lost power, from assuming the total load.
6.After the helicopter landed, the rotor blades and tail section struck a tree creating severe oscillations on the ground, which resulted in both engines breaking free from the airframe, causing the engines to injest varying amounts of debris from the broken engine mounts and foreign object damage shield.
Findings as to Risk
1.The aircraft maintenance engineer was not secured in the cabin seat and, as a result, was injured by repeated contact with the interior cabin structure near the cockpit entry.
2.Although the pilots were not injured during the severe ground oscillations, the damage to their protective helmets - and the potential risk of serious head injuries - would have been lessened had they been wearing their available shoulder harnesses.
3.In each engine, the locknut of the number 1 bearing on the front compressor disc shaft was intentionally overtorqued during overhaul assembly, collapsing the disc shaft and likely weakening the locknut. Had the locknut or shaft separated during engine operation, it is likely that catastrophic engine damage would have occurred.
Other Findings
1.The flyweight spring and bearings in the Ng governor on the number 2 fuel control unit were worn to limits, which affected the set points during the bench tests and may have caused inconsistent engine performance.
2.The data plates for the engines and power turbine assemblies each contained incomplete or inaccurate data, and were not in accordance with the engine manufacturer's instructions.
Accident investigation:
 |
|
Sources:
CADORS 2002P1434
http://www.tsb.gc.ca/eng/rapports-reports/aviation/2002/a02p0320/a02p0320.asp
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 25-Dec-2010 19:50 | slowkid | Added |
| 20-Dec-2012 07:47 | TB | Updated [Aircraft type, Cn] |
| 06-Jan-2015 17:26 | Aerossurance | Updated [Time, Departure airport, Destination airport, Source, Narrative] |
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