57-08-02 BELL: Applies to All Models 47B3, 47D, 47D1, 47G, and 47H1 Helicopters Equipped With Parker Check Valves in the Oil System.
Compliance required at next oil change and every 25 hours thereafter until replacement is accomplished.
Several failures of the hinge in the oil system Parker check valve, P/N 1111-517703, 1111-517704, or 1111-517744, have occurred resulting in restriction of the flow of oil from the pump. To preclude recurrence of such failures, the following must be accomplished:
1. At the next oil change and every 25 hours thereafter, remove, disassemble, and inspect the oil system Parker check valve, P/N 1111-517703, 1111-517704, or 1111-517744, for wear or failure of the hinge and freedom of operation. If defects are found, replace the valve.
2. James Pond Clark check valve, P/N 879A-10TT, has been approved as a replacement valve. The 25-hour inspection outlined above may be discontinued when the valve is installed.
(Bell Service Bulletin No. 119 dated March 15, 1957, covers this same subject.)