Thomas Frisch

To whomever it concerns, subject AD mandates the inspections according SB 737-27A1296 REV 00 for airplane with a compliance time of 12 or 30 days. It is also stated that the AD is an interim action and that an AD for airplanes with a different compliance time of 12 or 30 days is anticipated. Investigations showed that a supplier used wrong tooling in order to install the bearings in the aft lugs of the elevator tab control mechanism. As a specific line number has been identified (L/N 2508) since the tooling has been introduced / used in the final assembly line, an AD for airplanes prior the suspected line number is not required. Apparently, previous installation method of the bearing has been within specifications. So in my opinion, it does not make sense to "punish" operators with an additional inspection (even combined with an existing inspection task with the same inspection intervals), due to the fact that during final assembly of newer airplanes bad workmanship occurred. Up to now, the current design on airplanes prior L/N 2508 has been proven reliable. In addition: One question of mine is, what background data supports the interval of 2000FC or 4000FH. I doubt that subject inspection is effective, as up to now, degradation of correct installed bearings is not given. For wrong installed bearings however, the degradation would seem to be too high, as a threshold of 12 and 30 days has been chosen. Findings should confirm this. However, there is the possibility that some operator could have installed a suspect elevator tab control mechanism on airplanes having a long compliance time. Operators could show compliance with a future AD if maintenance data shows that suspect P/N has not been replaced. If such data is not available, an inspection - with an appropriate interval - has to be performed. Thanks