30 April 2001
Main Rotor Blade Cracks
A Canadian 369D operator involved in repetitive heavy lift operations has submitted a Service Difficulty Report (SDR) of cracks on all five main rotor blades (P/N 369D21100-523).
During installation of the main rotor blades following scheduled mast replacement, chordwise cracks were found on the underside doubler at the outboard end of the blade root fitting. The cracks had penetrated completely through the doubler, apparently during the 87 hours since the previous 100-hour inspection. Time since new (TSN) was 1,869 hours.
A precautionary inspection was carried out on a sister ship operated by the same company. Smaller cracks were found in the same area on all five main rotor blades, which had a TSN of 1637 hours. All ten of the subject blades also exhibited paint cracking or separation of the squeeze-out adhesive bond at the outboard end of the attachment fitting. The P/N 369D21100-523 blades have an airworthiness life limitation of 3,530 hours.
The ten blades have been returned to the manufacturer for investigation, and Transport Canada has contacted the FAA to address the apparent lack of inspection criteria, both in the maintenance manual and FAA ADs with respect to the -523 blade. In the interim, Transport Canada strongly recommends that operators of 369D and 369E helicopters pay particular attention for cracks on the underside doubler area of the main rotor blades during each 100-hour inspection. Owners/operators who average more than six Torque Events (TE) per hour should refer to McDonnell Douglas Helicopters Service Letter 113.
Main rotor blade with visible crack line
Any further defects or occurrences should be reported by sending a Service Difficulty Report to Transport Canada, Continuing Airworthiness, Ottawa.
For further information, contact a Transport Canada Centre, or Mr. Barry Caldwell, Continuing Airworthiness, Ottawa, telephone (613) 952-4358, facsimile (613) 996-9178 or e-mail firstname.lastname@example.org.
For Director, National Aircraft Certification
Chief, Continuing Airworthiness