Incident Overview
On September 11, 2024, at approximately 1400 eastern daylight time, a Hughes 369D helicopter (registration N8969F) sustained substantial damage during an accident near Canton, Michigan. The commercial pilot was uninjured. The flight was conducted under Title 14 Code of Federal Regulations Part 133 as a rotorcraft external load operation.
Flight Purpose and Operation
The helicopter was supporting powerline maintenance work with low-level flights. It operated from an off-airport landing zone and was conducting Class B cargo delivery to a powerline structure located about 300 yards from the landing zone.
In-Flight Vibration and Precautionary Landing
While flying, the pilot—stationed in the left seat—noted an “intermittent and unusual vibration.” In response, the pilot performed a precautionary landing back at the landing zone and shut down the helicopter without further incident.
Postflight Inspection and Damage
During a postflight inspection of the main rotor system, the pilot observed a crack in the yellow main rotor blade. The blade, painted white, had sustained a chordwise crack outboard of the root fitting, near the doubler. The crack appeared to propagate from the blade’s trailing edge through both the upper and lower skins, stopping short of the leading-edge spar area.
The helicopter sustained substantial damage only to the yellow main rotor blade. No other damage occurred. The main rotor blades did not strike any birds, objects, or terrain during the flight.
Blade Details and Examination
The yellow main rotor blade was removed from the helicopter and transported to the NTSB Materials Laboratory in Washington, District of Columbia, for further examination. The blade was manufactured by MD Helicopters (part number 369D21100-523, serial number 009999-K364). At the time of the accident, the blade had accumulated 3,289.9 total hours, with 12.4 hours since its last inspection.
Aircraft and Engine Information
The airframe, manufactured in 1978, had accumulated 18,318.8 total hours. The helicopter was equipped with a Rolls-Royce 250-C20B turboshaft engine. The Federal Aviation Administration Type Certificate H3WE for the helicopter is currently held by MD Helicopters in Mesa, Arizona.
Flight Manual Procedures
The FAA-approved MD Helicopters MD 500D (Model 369D) Rotorcraft Flight Manual discusses abnormal vibrations in the emergency procedures section. It states:
Indications: Sudden, unusual, or excessive vibrations occurring during flight.
Conditions: The onset of unusual or excessive vibrations in the helicopter may be an indication of problems in the rotor or drive train systems.
Procedures:
- Land as soon as possible.
- No further flights should be attempted until the cause of the vibration has been identified and corrected.