Addressing a well-known area of concern on turbocharged engines, the FAA recently published a notice of proposed rulemaking on nearly all Lycoming and Continental turbocharged models, including those used in Twin Commanders. This sweeping AD would add to the nearly 20 others the FAA has adopted over the years directed at these parts.
V-band couplings are simple clamps used to secure the tailpipe to the turbocharger exhaust housing. The bands are secured with a t-bolt and trunnion mechanism that is either riveted or spot-welded on. Over time those areas can generate cracks, potentially causing a failure of the clamp. According to the FAA, the majority of problems have originated with the spot-welded variety.
If adopted, the AD would require yearly visual inspections of the clamps, and mandatory replacement at 500 hours time-in-service. While not a particularly expensive part or inspection, it will be the first time Twin Commanders are included in the requirements, so operators should make note. Specifically, models 500, 500A, 500B, 500S, 500U, 560A, 560E, and 685 are included in the proposal.
The FAA has published an extensive document addressing “Best Practices” for maintaining the clamps. It’s available on the agency’s website.
Comments on the proposed AD are due by November 4. You can find the full proposal and comment online.
