AD 80-21-53

80-21-53 ROBINSON HELICOPTER: Amendment 39-3989. Applies to Model R-22 Helicopters, certified in all categories, fuselage numbers 0006 through 0060, with spiral bevel gear sets numbered 39 through 210 installed in the main rotor transmission.

Compliance is required prior to further flight unless already accomplished.

To prevent tooth failure of the spiral bevel gear in the main rotor transmission and possible loss of power to the main rotor system, accomplish the following:

(a) Prior to further flight and at intervals not to exceed 10 hours' time in service thereafter, inspect the main transmission gear teeth in accordance with paragraph "Inspection Procedure" of Robinson Helicopter Company Mandatory Service Bulletin SB-5, dated October 6, 1980.

(b) If gear tooth spalling, or cracks are detected, or if chips are found on the sump magnetic chip detector plug, remove the main transmission from service.

(c) In the event that the MR (main rotor) chip light comes on during flight, make a precautionary landing as soon as possible and remove the transmission from service.

(d) Flight is prohibited without an operable MR chip detector system. Prior to each flight the pilot must perform a MR chip light check by grounding the electrical terminal of the chip detector at the bottom of the main transmission and checking to be sure the MR light on the instrument panel illuminates. The pilot must be trained by a certified mechanic to perform this check. This check constitutes preventative maintenance and may be performed by persons authorized to perform preventative maintenance under FAR 43. The check required by this paragraph may be performed by the pilot.

(e) All gear sets numbered 39 through 210 must be removed from service no later than January 31, 1981. Replacement of these gear sets constitutes terminating action for this AD.

(f) Special flight permits may be issued, in accordance with FAR 21.197 and 21.199, to operate helicopters to a base for the accomplishment of inspections required by this AD.

(g) Alternative inspections, modifications, or other actions which provide an equivalent level of safety may be used when approved by the Chief, Engineering and Manufacturing Branch, FAA Western Region.

This amendment becomes effective December 18, 1980 to all persons, except those to whom it was made immediately effective by telegraphic AD T80-21-53, dated October 11, 1980.