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ASN Wikibase Occurrence # 205770
Last updated: 17 November 2020
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Type:Silhouette image of generic AS50 model; specific model in this crash may look slightly different
Eurocopter AS 350B3
Registration: N413LP
C/n / msn: 3228
Fatalities:Fatalities: 0 / Occupants: 2
Other fatalities:0
Aircraft damage: Substantial
Location:San Juan, PR -   United States of America
Phase: Unknown
Departure airport:San Juan, PR (TJIG)
Destination airport:San Juan, PR (TJIG)
Investigating agency: NTSB
The pilot/owner of the turbine helicopter was practicing autorotations with a flight instructor. After completing several autorotations uneventfully, the instructor asked if he could perform one, and the pilot agreed. Near the flare at the end of the maneuver, the pilot heard the engine overrev, followed by an Nr (rotor speed) aural warning, followed by a fire warning light illumination on the instrument panel. After landing, the pilot exited the helicopter with a fire extinguisher and attempted to extinguish an engine fire.
Review of data downloaded from a vehicle-engine multifunction display and digital engine control unit revealed that the first failure recorded during the flight indicated that the gas generator rotation speed (N1) reached an out-of-limit value. At that time, the fuel regulation was in mixed mode, as the collective twist grip throttle control was out of the “flight” detent and the pilot was manually controlling the throttle. A second failure was recorded 2 seconds later, which indicated that the free turbine rotation speed (N2) reached an out-of-limit value. The failure was triggered by the maximum recorded value of 545 rpm, which equated to a turbine speed (Nr) of 140%.
The engine’s freewheeling turbine was designed to separate turbine blades at 150% Nr in order to prevent the turbine disc separating at 170% Nr. It is likely that the flight instructor excessively opened the fuel metering unit via the twist grip throttle manual control, which resulted in an engine overspeed, turbine blade separation, and subsequent engine fire.

Probable Cause: The flight instructor's incorrect manipulations of the twist grip throttle control during a practice autorotation, which resulted in an engine overspeed and subsequent fire.



Accident investigation:
Investigating agency: NTSB
Status: Investigation completed
Duration: 11 months
Download report: Final report

Revision history:

07-Feb-2018 13:48 ASN Update Bot Added

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