N8969FHughes Helicopters HUGHES 369D · 1978

On September 11, 2024, about 1400 eastern daylight time, a Hughes 369D helicopter, N8969F, sustained substantial damage when it was involved in an accident near Canton, Michigan. The commercial pilot was uninjured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 133 rotorcraft external load flight.

The purpose of the low-level flight was to support powerline maintenance work. The helicopter was operating from an off airport landing zone and conducting Class B cargo delivery to a powerline structure about 300 yards from the landing zone.

While in flight, the pilot, who was stationed in the left seat, noticed an “intermittent and unusual vibration” with the helicopter. The pilot performed a precautionary landing to the landing zone, and he shut down the helicopter without further incident. The pilot performed a postflight inspection on the main rotor system and he observed a crack in the yellow main rotor blade (main rotor blades are typically marked with various colors to easily identify and reference each individual blade).

The yellow main rotor blade, which was 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 to the yellow main rotor blade. There was no further damage sustained to the helicopter. The main rotor blades did not strike any birds, objects, or terrain during the accident flight. The yellow main rotor blade was removed from the helicopter, and it was transported to the NTSB Materials Laboratory, Washington, District of Columbia, for further examination.

The yellow main rotor blade was manufactured by MD Helicopters (part number 369D21100-523 and serial number 009999-K364). At the time of the accident, the yellow main rotor bade had accumulated 3,289.9 hours and 12.4 hours had elapsed since the last inspection was performed on the yellow main rotor blade.

At the time of the accident, the airframe, which was manufactured in 1978, had accumulated 18,318.8 hours. The helicopter was equipped with a Rolls-Royce 250-C20B turboshaft engine.

The Federal Aviation Administration (FAA) Type Certificate for the helicopter, H3WE, is currently held by MD Helicopters, Mesa, Arizona.

The FAA-approved MD Helicopters MD 500D (Model 369D) Rotorcraft Flight Manual discusses abnormal vibrations in the emergency procedures section and 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.