Prompted By Reports Of Cracked Main Rotor Blades

The FAA is proposing a new AD for MDHI Model 369A, 369D, 369E, 369FF, 369H, 369HE, 369HM, 369HS, 500N, and 600N helicopters. This proposed AD would require inspecting each main rotor blade (MRB) for a crack. This proposed AD is prompted by reports of cracked MRBs.

This proposed AD would require repetitively inspecting the MRB trim tab for gouges, nicks, scratches, and cracks.

This proposed AD is prompted by reports of two operators finding cracks on an HTC-manufactured MRB. In both cases, the cracking was located on the MRB skin adjacent to the trim tab, and they were discovered following flights in which an increase in vibration levels was noticed. HTC determined the root cause of the cracking to be fatigue. HTC also stated that there was evidence of impact damage, filing, and sanding under the paint of the cracked MRBs. If not detected and corrected, this condition could result in failure of an MRB and subsequent loss of control of the helicopter.

This proposed AD would require, within 25 hours time-in-service and thereafter at each 100-hour or annual inspection, inspecting each MRB trim tab end at the trailing edge corner where the trim tab and MRB meet for cracks, and inspecting the top and bottom surface of each MRB for a crack in the area adjacent to inboard trim tab the trim tab corner for a crack, from the trailing edge towards the leading edge. If there is a crack, this proposed AD would require replacing the MRB.

The FAA estimates that the AD would affect 622 helicopters of U.S. Registry.

At an average labor rate of $85 per work-hour, operators may incur the following costs in order to comply with this AD:

• Inspecting one MRB would require about 0.1 work-hour, for a cost-per-helicopter of $43 for MDHI Model 369-series and 500N helicopters, and $51 for MDHI Model 600N helicopters.
• If required, replacing one MRB would require 3 work-hours, and required parts would cost $13,000, for a cost per MRB of $13,255.

Comments on the proposed AD must be received by January 25, 2019.

(Image from file)

FMI: Proposed AD