Pilot Debrief

AIRBUS EC130 near Hanalei, HI — 2016-01-18

Final reportWPR16FA055
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Date
2016-01-18
Location
Hanalei, HI, USA
Airport
PHLI
Aircraft
AIRBUS EC130
Registration
N11VQ
Category
Helicopter
Highest injury
Serious
Fatalities
0
Phase of flight
Cruise

Probable cause

The fatigue failure of the engine fuel pipe as a result of vibration caused by a worn starter-generator front bearing support, which excited the fuel pipe and caused it to oscillate at a resonant frequency, and a subsequent loss of engine power due to fuel starvation. Contributing to the severity of passenger injuries was the improper positioning of the passengers' seat belts.

Contributing factors

Contributing to the severity of passenger injuries was the improper positioning of the passengers' seat belts.

NTSB narrative

During an air tour flight, the helicopter was about 1/4 mile offshore at 1,450 ft mean sea level (msl) when the pilot heard the low rotor rpm warning horn. He immediately entered an autorotation and turned toward the beach. As he approached the shoreline at 374 ft msl, he made a sharp right turn to avoid large boulders in his intended landing area. The helicopter subsequently landed hard on the beach, bounced, and came to rest. Examination of the engine revealed that the main fuel injection pipe between the fuel valve assembly and the injection union was cracked and broken at the injection union B-nut connection. Subsequent engine test runs revealed that the starter-generator imparted a vibration into the engine that excited the fuel pipe to vibrate in resonance and ultimately fracture due to reverse bending fatigue at the flared end. The crack or fracture of the fuel pipe allowed pressurized fuel to escape, reducing fuel flow and pressure to the injection manifold below that which was required to sustain combustion, and resulted in the loss of engine power. The vibration imparted into the engine by the starter-generator remained below the global vibration limit for the entire engine, but was sufficient to excite the fuel pipe. Examination of the starter-generator revealed that the front bearing outer race and support exhibited signatures consistent with fretting and pronounced wear. This observed wear of the front bearing support allowed the armature to oscillate and impart a vibration into the engine frame. Further, the investigation was unable to determine when the vibration began and if the fatigue crack had already started at the time of the last inspection. Without a requirement to look at the front bearing and the shaft play, the operator would have no way to identify the vibration issue. Onboard video imagery recorded during the accident flight confirmed that the pilot's harness lap belt was positioned properly, low and tight across his hips. Of the six passengers onboard, four passengers' lap belt positioning were visible in recorded cabin imagery, and depicted that the lap belts were not tight across their hips and that the buckle was at or above their waists. Examination of the pilot's seat revealed vertical displacement consistent with a significant amount of vertical energy being absorbed by the seat during the hard landing. Two of the passenger seats displayed some vertical displacement, two displayed minimal vertical displacement, and two seats showed no vertical displacement. The seat displacement was directly related to the amount of vertical energy absorbed by the seat and to the severity of the occupant's injuries. The loose and out-of-position seatbelts most likely allowed the passengers' bodies to shift out of position on the seat before and during the hard landing and did not restrain the occupants in the proper position for the seat to absorb the vertical landing loads for which it was designed.

Analysis

Primary failure mode
Engine power loss
First missed decision gate
Pilot could have checked engine performance before departure.

NTSB coding

Evidence available

  • Video
  • Photos
  • 27 docket documents
View NTSB final reportView NTSB docket

Docket documents27

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