Tech Tip 2013-001

ATA:                     63

Aircraft Model:       AS350

Subject:               Main Rotor Gear Mods and TBO

Date:                   February 11, 2013

The Master Servicing Manuals for the AS 350 series has been amended in the recent past to include the increased Time Before Overhaul of the main rotor gear box if certain modifications are embodied and operating conditions are met.

The modifications required are listed in the MSM however there may have been some confusion as to embodiment of one of the mods and part number of the main gear box.

The three modifications are as follows:

  • 07-7175, SB 63-00-09, installation of the longer chip detector
  • 07-7162, SB 63-00-12, installation of the spin on filter
  • 07-7203, installation of the hardened gear set

Most operators have previously installed the longer electric chip detector since it was a simple operation that could be carried out in the field. However there was no guarantee that each gear box would accept the longer detector since some main housings would require machining. These housings generally were modified when the gear box was sent for overhaul.

The spin-on transmission oil filter was another simple and easy modification for the operator which has also found fairly wide acceptance for field installation.

The hardened gear set would be installed during overhaul or major repair if replacement became necessary. In some cases incorporation of some or all of these modifications would change the dash number of the main gear box from a -04 to a -05. However it is possible to have a -05 main gear box that does not have mod 07-7203, hardened gear set, incorporated since there are other part number gear sets that are eligible to be installed in a -05 gear box.

Operators must confirm that all three modifications have been embodied and recorded on the gear box log card to extend the TBO to 3800 hours. An additional 400 hours can be added to the TBO if the gear box has been operated on mineral oil since new or last overhaul. A margin of 300 hours/180 days is also available for all main gear box TBO’s.