is calling for repetitive inspections and eventual replacement of Engine Components Inc. (ECi) and Airmotive Engineering “Titan” cylinders found on 6,000 Continental 520 and 550 model reciprocating engines at a cost that could reach $82.6 million.
ECi, objected to the proposal, saying the required actions “will degrade safety, not improve it” by requiring thousands of premature top overhauls. “Industry experience shows that there is a substantial risk of catastrophic engine failure following such top overhauls,” ECi says.
FAA says the proposed airworthiness directive, issued Aug. 12, stems from investigations into numerous reports of cylinder head-to-barrel separations and cracked and leaking aluminum cylinder heads on the affected assemblies.
Research discovered two “independent failure modes” that cause the cylinder head separations, but the root cause of those failures cannot be definitively pinpointed, the agency says. One failure mode involves cracking that stems from the internal dome radius of the cylinder head, and the second involves cracking at the cylinder head-to-barrel threads.
The proposal follows a series of meetings and correspondence between, ECi, Airmotive Engineering Corp. (an ECi affiliate company which had been the production approval holder for Titan assemblies),and FAA, considering ramifications of potential requirements and alternatives, FAA maintains.
“Knowing the likely impact that compliance with the AD will have upon the owners and operators, a detailed review was performed to consider all aspects of the information provided by Airmotive Engineering Corp.,” FAA says. But it adds that after conducting a risk assessment, “we concluded that proceeding with this proposed AD to correct the unsafe condition was appropriate.”
FAA, the NTSB and industry have grappled with problems of cracked cylinder heads for years. FAA has issued a series of ADs and the NTSB, which has focused on assembly failures since 2000, last year issued a recommendation for inspection and replacement of certain ECi assemblies.
FAA and NTSB in 2005 formed a task force to study failure of cylinder heads in general. That task force made several site visits, including to ECi to discuss manufacturing processes. After developing a test facility and running numerous tests, ECi changed its manufacturing process for cylinder assemblies in October 2009. ECI notes that there had been no reported failures on affected assemblies produced after October 2009. “Although ECi’s changes to the manufacturing process may increase the fatigue strength of new production cylinder heads, a large population of potentially discrepant cylinder assemblies remains in service without any required corrective action,” NTSB had stated.
ECi notes the FAA proposal goes even further than the NTSB recommendation to include many more assemblies. “ECi believes that the FAA’s proposed AD is unwarranted, inappropriate, and unnecessarily punitive for the owners of the affected aircraft,” the company says, noting the action was prompted by 30 instances (out of 30,000 installed) of head-to-barrel junction failures in Titan cylinders. None of those resulted in accident or injury, the company adds.
The company further contends that there have been more than 1,200 similar head-to-barrel failures in 520/550 cylinders manufactured by other production approval holders, but FAA has not taken action in those cases.
FAA is proposing initial and repetitive inspections, replacement of cracked cylinders and replacement of cylinder assemblies at reduced times-in-service. It would further prohibit installation of the affected assemblies into any engine.
The proposed AD would break the affected cylinders into two groups based on Serial Number (S/N): SN 1-33696 (Group A) and S/N 33697-61176. (Group B). The proposal would require removing Group A cylinder assemblies from service within 25 hr. of the effective date if the operating hours are either fewer than 500 hr. or more than 1,000 hr. Group B cylinder assemblies with 1,000 or more operating hours would need replacement within 25 operating hours following the effective date of the AD.
The proposed AD would require repetitive visual inspections, compression tests and leak checks for cracks on Group A assemblies with between 500-1,000 operating hours and on Group B assemblies with fewer than 1,000 hr.
The proposed AD further would bar installation of the affected assemblies onto any engines, and calls for reporting the removed assemblies to FAA.
FAA is accepting comments on the AD through Oct. 11.