AD 86-16-11 L

86-16-11 BELL HELICOPTER TEXTRON, INC.: Letter issued August 12, 1986. Applies to all Bell Helicopter Model 412 helicopters, S/N 33001 through 33118, 33120 and 33121, certified in any category.

Compliance required as indicated unless already accomplished.

To prevent failure of the tail rotor control, accomplish the following:

(a) Within 20 hours' time in service after receipt of this AD, visually inspect the T/R hub assembly P/N 212-011-701-3, in accordance with Part I of Bell Helicopter Textron, Inc. (BHTI), Alert Service Bulletin (ASB) 412-86-25, Revision "A," dated July 23,1986.

(1) If the (P/N) 212-011-716-1 T/R trunnion housing is cracked or there is axial play in the T/R trunnion, or if there are excess balance washers, comply with Part II of the Alert Service Bulletin before further flight.

(2) Repeat this inspection every 20 hours' time in service until paragraph (b) of this AD is accomplished.

(b) Remove the 212-011-701-1 T/R hub and bladeassembly and inspect the trunnion bearing housing, P/N 212-011-716-1, as detailed in Part II of BHTI ASB 412-86-25, Revision "A," dated July 23, 1986, within 150 hours' time in service or within 60 days after the issue date of this AD, whichever occurs first. Replace any housing having an end web thickness of .059 inches or less with a serviceable part.

An alternate method of compliance or adjustment of the compliance time, which provides an equivalent level of safety, may be approved by the Manager, Helicopter Certification Branch, Aircraft Certification Division, FAA, Southwest Region.

This airworthiness directive becomes effective upon receipt.