29 December 2003
Crankshaft Fatigue Cracks
Recently, two Canadian operators have reported in-flight engine failures and the cause was later attributed to failed crankshafts on the TIO-540-J2BD and TIO-540-A2B engines. Fortunately, both aircraft were a twin-engine configuration, and landings were performed using the remaining engine.
Lycoming has stated that neither of these crankshafts were affected by Mandatory Service Bulletins 552 or 553 which were material-related. Lycoming also stated that the part numbers found on these crankshafts indicate the they were manufactured at least 15 years prior to the production of similar crankshafts affected by SBs 552 and 553.
The Canadian Transportation Safety Board (TSB) later examined these two failed crankshafts and concluded that fatigue cracks were the root cause of failure. The inspection method to detect crankshaft fatigue cracks is conducted using a magnetic particle inspection (MPI), and the opportune time is at engine overhaul.
Both of the failed crankshafts on the aforementioned engines were on Transport Canada approved extended TBO (time between overhaul), and had logged 2175 and 2764 hours respectively. Airworthiness Notice (AN) B041, Edition 3, was the means by which these engines were approved for the extended operation past the manufacturer's recommended TBO of 1800 hours.
Lycoming Service Instruction No. 1009AQ recommends that these engines be overhauled at 1800 hours. However, Lycoming will allow an extension of 200 hours for engines that are in "frequent" type service; accumulating 40 hours of service per month consistently since being placed in service. Alternatively, Transport Canada Principal Maintenance Inspectors (PMI) may approve operators, on a case-by-case basis and by oil sampling and in accordance with AN B041 Edition 3, to extend their engine TBOs, sometimes well beyond that recommended by the manufacturer.
Further to the above, Transport Canada reminds operators to carefully read AN B041, Edition 3, before requesting any piston engine to be extended past the manufacturer's recommended TBO; keeping in mind that the only ideal time to inspect the engine crankshaft is at overhaul.
Any defects or further occurrences, should be reported by sending a Service Difficulty Report (SDR) to Transport Canada, Continuing Airworthiness, Ottawa, Ontario.
For further information, contact a Transport Canada Centre (TCC), or Mr. Barry Caldwell, Continuing Airworthiness, Ottawa, telephone (613) 952-4358, email@example.com.
For Director, Aircraft Certification
Chief, Continuing Airworthiness
Note: For the electronic version of this document, please consult the following Web address: https://tc.canada.ca/en/aviation/aircraft-airworthiness/aircraft-certification