ROBINSON R44 near Orlando, FL — 2017-04-20
- Date
- 2017-04-20
- Location
- Orlando, FL, USA
- Aircraft
- ROBINSON R44
- Registration
- N899GB
- Category
- Helicopter
- Highest injury
- None
- Fatalities
- 0
- Phase of flight
- Descent
Probable cause
A partial failure of the helicopter's engine tachometer due to the separation of one of the magnet assemblies and engine roughness, which precipitated the pilot’s initiation of an off-airport autorotation, during which he applied improper aft cyclic flight control input, which was contrary to the Pilot’s Operating Handbook. The reason for the reported engine roughness could not be determined during postaccident examination and engine test-runs.
NTSB narrative
The commercial pilot was conducting a local sightseeing flight in a helicopter with two passengers onboard. He reported that, while he was flying southbound and descending from 1,000 to 600 ft, he heard a "pop" sound and noted a corresponding right yaw, followed by vibration and engine roughness. The pilot looked at the instruments, and the main rotor tachometer was indicating that the rpm had dropped to "0" and that the engine tachometer was indicating between 60% and 70%. The pilot immediately initiated an autorotation to a median, and the helicopter landed hard. The helicopter began rolling forward, and in response, the pilot applied aft cyclic control input, which was contrary to the instructions in the Pilot's Operating Handbook, which contained a caution in the emergency procedures section related to power failures that stated to "not apply aft cyclic during touchdown…to prevent possible blade strike to the" tailboom. The pilot's improper control input resulted in the main rotor blades contacting and substantially damaging the tailboom. Postaccident examination of the engine and the tail rotor drive system revealed no evidence of any preimpact mechanical failures or malfunctions that would have precluded normal operation. The engine was test-run, and it started and operated normally. One of the two main rotor tachometer indication system magnet assemblies was separated and not recovered. According to helicopter manufacturer personnel, with only one magnet assembly installed, the main rotor tachometer rpm would indicate about 50% of the actual rotor rpm. Therefore, the main rotor tachometer rpm indication was likely erroneous due to the separation of a magnet assembly from the rotor rpm sensor. The pilot's perception that the main rotor tachometer had decreased to "0" was likely in response to his seeing the needle near the lowest number on the scale. The reason for one of the magnet assemblies' separation could not be determined because it was not located.
Analysis
- Primary failure mode
- Mechanical failure
- First missed decision gate
- Pilot could have checked engine instruments before descent to identify issues.
NTSB coding
Evidence available
- Photos
- 7 docket documents