N280WREnstrom Helicopter 280C · 1977

On March 16, 2024, about 1645 central daylight time, an Enstrom Helicopter Corporation 280C helicopter, N280WR, was substantially damaged when it was involved in an accident near Port Lavaca, Texas. The pilot was not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot reported that, earlier that day, he flew a 2-hour flight and landed at an airport about 5 miles from his home for refueling. He stated that, after refueling, the engine started normally but that, when he initiated a hover, the overboost warning light illuminated. He stated that he adjusted the manifold pressure lower, the overboost warning light extinguished, and he flew the helicopter home and landed in his front yard uneventfully.

The pilot reported that, when he initiated a hover to reposition the helicopter to a moveable landing platform, the overboost warning light immediately illuminated. He stated that, while he was “in the process of adjusting to position [the helicopter] on the platform,” the engine lost power, and the helicopter settled with only the right skid on the platform. The helicopter subsequently rolled to the left, and the main rotor blades contacted the ground. The helicopter sustained substantial damage to the main rotor, tail rotor, tailboom, and stabilizers.

A postaccident examination of the engine fuel system revealed that the fuel injector servo idle mixture was set in excessively rich position. A review of maintenance records revealed that, during the most recent annual inspection completed in December 2023 (at a helicopter total time of about 7 flight hours before the accident), the “idle mixture adjustment and fuel pressure [were] found to be incorrect,” which was addressed by “set[ting] idle mixture and fuel pressure per Enstrom [Maintenance Manual] and Lycoming [Operator’s Manual].

The pilot reported that, after the maintenance performed during the annual inspection was completed, he had to manually lean the mixture at idle and low power settings to prevent the engine from running excessively rich. (The manual fuel mixture control provides the pilot with the option to manually lean the mixture for best cruise power or best specific fuel consumption by effectively reducing the size of the metering jet. It also provides the means to shut off fuel flow to the engine at engine shutdown.) According to the Enstrom 280C Rotorcraft Flight Manual, the mixture must be full rich for landing and takeoff, regardless of power, for proper engine cooling.

The helicopter is equipped with Lycoming HIO-260-E1AD engine and a Rajay turbocharger. The turbocharger installation utilizes no waste gate or mechanical controls, and is equipped with a fixed exhaust pressure bypass. According to the Enstrom 280C Maintenance Manual Supplement, “Pilot operation of the Enstrom turbocharged system is the same as the normally aspirated system except the pilot must not exceed 36.5” of manifold pressure and must monitor the total inlet temperature to the turbine by a proper mixture control schedule”

Enstrom Helicopter Corporation SIL No. 0069, “Engine Troubleshooting Procedures for Turbo Installations and Idle Adjustments to Correct Engine Roughness and/or Inadvertent Stoppage,” dated October 7, 1977, provided technical guidance for field adjustments to the fuel system. According to the SIL, an improperly adjusted idle mixture can result in engine roughness or inadvertent engine stoppage, particularly during rapid throttle deceleration or during operations at low power settings. The SIL outlined specific procedures for verifying and adjusting the idle mixture to ensure the proper fuel-to-air ratio is maintained for turbocharged engine installations.