The FAA is proposing a new Airworthiness Directive mandating repetitive inspections of MD Helicopters single-engine 369, 500, and 600 models for main rotor blade (MRB) trim tab for gouges, nicks, scratches, and cracks. The AD covers MRBs manufactured by Helicopter Technology Co. (HTC) and covers part numbers 369A1100, 369D21100, 369D21102, 369D21120, 369D21121, 369D21123, 500P2100, and 500P2300.
It was prompted by the discovery of cracks on two HTC-manufactured MRBs by two operators. In both cases, the cracks were located on the MRB skin adjacent to the trim tab that produced increased vibration in flight. The condition could result in MRB failure and aircraft loss, the FAA said.
HTC has determined that the cracking’s root cause is fatigue and found evidence of impact damage, filing, and sanding under the paint of the cracked MRBs. It issued a related Service Bulletin in May 2017 (SB 2100-9). The proposed FAA AD would require initial MRB inspections within 25 hours time in service and at each annual or 100-hour inspection. If cracks are found, the MRB must be replaced at an estimated cost of $13,255.