Airbus AS350 B2 N814EH

Summary

On 13 March 2015 at about 15:15 local time, a Airbus AS350 B2 registered N814EH, operated by Erickson Helicopters, was involved in an accident near Anchorage, Alaska, United States. 3 people were on board and nobody was injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

13 March 2015 at 15:15

Classification

Accident

Location

Anchorage, Alaska, United States

Coordinates

61.2286, -150.8708

Aircraft

Airbus AS350 B2

Registration

N814EH

Category

Helicopter

Year built

1992

Engines

1

Operator

Erickson Helicopters

Operating rule

Part 135: Air Taxi & Commuter

Phase of flight

Not recorded

Route

Anchorage → Beluga

Aircraft damage

Substantial

Weather

VMC

Light

Night/Bright

NTSB number

ANC15LA015

Nobody was injured.

The failure of the ball bearing within the pitch change spider assembly due to its operation with no grease within the bearing, which resulted in the subsequent fracture of the spider assembly and a loss of tail rotor control authority. Also causal to the accident were the overhaul facility’s failure to follow the helicopter manufacturer’s spider assembly overhaul procedures, which resulted in the assembly leaving the facility with no grease in the bearing, and the mechanic’s failure to complete all of the tasks on the 600-flight-hour/24-month inspection checklist, which led to the lack of grease in the bearing going undetected.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

The commercial pilot was conducting a 14 Code of Federal Regulations Part 135 on-demand charter flight in the helicopter. The pilot reported that, while the helicopter was in cruise flight, about 1,000 ft above ground level, he felt a "clunk" in the tail rotor control pedals. Immediately thereafter, the helicopter began to yaw left. The pilot attempted to counteract the yaw by pressing the right tail rotor control pedal up to its forward stop, but the helicopter did not respond. The pilot declared an in-flight emergency with air traffic control, returned to the departure airport, and executed an emergency run-on landing. An examination of the helicopter revealed that the tail rotor pitch change spider assembly had fractured into two pieces with rotational scarring present along the fractured surfaces; the inside of the spider assembly exhibited dark discoloration consistent with thermal damage. Half of the inner race of the ball bearing within the spider assembly was found loose on the tail rotor gearbox output shaft. Further examination revealed that the spider assembly failure was consistent with bearing seizure. No evidence of grease was found on the bearing surfaces or the bearing housing. A review of maintenance records revealed that, about 13 months before the accident, the pitch change spider assembly was overhauled by a certified repair station, during which the original ball bearing was replaced. According to the helicopter manufacturer's spider assembly overhaul procedures, grease was to be applied during the installation of the new bearing. The spider assembly was installed on the helicopter by the operator's maintenance personnel about 1 month later, at which time a mechanic signed off completing the helicopter manufacturer's 600-flight-hour/24-month inspection checklist, which included regreasing the bearing. The bearing failed about 10 months and 141 flight hours after the spider assembly was installed on the helicopter. Given that no grease was found on the fractured components and that the signatures were consistent with thermal damage due to a bearing seizure, it is likely that the overhaul facility did not follow the helicopter manufacturer's overhaul procedures and failed to apply grease to the bearing. During the subsequent installation of the overhauled spider assembly, it is likely that the mechanic presumed that the newly overhauled spider assembly bearing contained grease and, therefore, did not complete the bearing regreasing procedure in accordance with the inspection checklist, which led to the lack of grease in the bearing going undetected.

Quoted verbatim from the NTSB record.