Alan Faulks

With reference to this NPR, our company recently (April 2012) suffered an in-flight failure of one grip as described in the NPR. I wish to comment that the proposed life limit is not practical in that: 1. The proposed life of 25,000 cycles for the P/N 204-011-121-121 grip is higher than the proposed life of 15,000 cycles for the P/N 204-011-121-009 grip. The OEM has advised us that the number of in flight incidents concerning the grip tang failures has been related more towards to the -121 version than other part numbers. Logically, the life of a failure prone part should be lower, not higher. 2. In our recent failure which occurred on a -121 grip, the TSN of the grip was 4,900 hrs. This is far short of the suggested retirement time. This suggests high cycle fatigue is n 3. Time since last NDT inspection was only 57 hrs out of a 150 hr inspection cycle.T 4. The 150 hr inspection cycle for the -121 part is much lower than the 400 hr inspection cycle for the -009 part. This indicates there is some reason for the lower inspection period on the -121 grip I would suggest some more research be done to obtain more history of these failures to determine the Mean Time between Failures of these components..A more practical figure could be assigned based on this. In addition, the suggested method of calculating a "life" for components which have no previous documented service life is impractical. Grips are often in storage as spare parts or as a sub-component of a Main Rotor Hub assembly which is out of service for any one of many reasons. The assumption of assigning 50 hrs for each month of service may be acceptable but only for periods when the grip is know to have been placed in service. An alternative could be to assign a fixed high time (TSN) to a TSN unknown part which would allow the operator to plan for replacement at the next scheduled overhaul. In practice, many grips do not reach the 15,000 hr limit as they are scrapped for various other reasons.