Accident Overview
On March 5, 2023, at approximately 1400 Alaska Standard Time, an Enstrom F-28C helicopter, registration N5688R, was involved in an accident in Anchorage, Alaska. The helicopter was being operated as a personal flight under Title 14 Code of Federal Regulations Part 91. The pilot and passengers were not injured. The helicopter sustained substantial damage to the tail boom.
Pilot Report
The pilot reported that the preflight inspection and engine run-up were completed with no anomalies. The helicopter departed from Lake Hood Seaplane Base (LHD). During takeoff, at an altitude of about 30 feet above the ground, the helicopter could not maintain main rotor rpm. The pilot stated that the engine lost partial power and the helicopter was too low to perform an autorotation. A run-on landing was made to a snow-covered lake. The accident site showed buildings and parked airplanes in front of the departure path.
Engine Examination
An engine examination was conducted by a National Transportation Safety Board investigator. The engine started normally, responded to throttle inputs, and cylinder head temperatures were equal across all cylinders. Both magnetos were fully operational. Compression was good on all cylinders. The bottom spark plugs showed no electrode anomalies. The turbocharger had secure gaskets and hoses, and the fan moved freely. All intake and exhaust connections were secure and undamaged with no blockages. The main rotor blade belt tensioner operated normally and was engaged at the start of the examination. No anomalies were found with the main rotor drive belt. The main rotor transmission moved freely. The examination found no evidence of preimpact mechanical malfunctions or failures that would have precluded normal operation.
Maintenance History
An annual inspection, including a 100-hour engine inspection, was completed on May 5, 2022, with a satisfactory engine test run. On November 20, 2022, the main rotor blades were removed and the helicopter was placed in winter storage. On March 5, 2023, the main rotor blades were reinstalled, and the helicopter underwent run-up and hover checks, which were satisfactory.
References to Operating Handbook
The Federal Aviation Administration’s Helicopter Flying Handbook notes that as main rotor rpm decreases, engine horsepower also decreases, with a 10% loss in rpm resulting in a 10% loss of horsepower. If a pilot raises the collective to counter settling, the situation can worsen. The pilot’s operating handbook provides guidance for maximum power takeoffs from confined areas, emphasizing proper collective and throttle coordination to avoid overpitching, which can cause rotor and engine rpm to decrease.