76-05-11 ENSTROM: Amendment 39-2545. Applies to Enstrom Model F-28A and 280 helicopters certified in all categories with the following serial numbers:
F-28A Models - S/N 03 thru 347
280 Models - S/N 1001 thru 1030
Compliance required as indicated unless already accomplished:
(a) Within the next ten (10) hours time in service after the effective date of this AD remove the three (3) tail cone attach bolts and perform a dye penetrant inspection of the bolts for fatigue cracks or an equivalent inspection method approved by the Chief, Engineering and Manufacturing Branch of the Federal Aviation Administration, Great Lakes Region.
Note: Particular attention should be given to the threaded area and the radius under the base of the bolt head.
(b) Replace any defective bolts with a new bolt of the same part number or a stronger equivalent listed in paragraph (d) prior to further flight.
(c) Tail cone bolts of the original design shall be inspected again at 50 hours from the inspection required in paragraph (a) unless replaced with the stronger bolts as listed in paragraph (d).
(d) Within 110 hours time in service from the effective date of this AD unless already accomplished replace the three (3) AN bolts attaching the tail cone with the following NAS bolts:
Upper attachment point - NAS146DH-24 bolt
Lower attachment points - NAS146DH-22 bolt
MS20002C6 washers are to be installed under the head. Care should be exercised to insure that the proper bolt grip length is maintained.
(e) Torque bolts to 240 in. - lbs. and safety wire.
(f) Upon compliance with paragraphs (d) and (e) the inspections listed in paragraph (c) are no longer required.
Note: When installing the NAS hardware on some helicopters in the field, it may be necessary to install an additional MS20002C6 or an AN 960-616 washer on the NAS bolts. The additional washers will insure that the bolts will not bottom out on the grip portion of the bolt when torqued to the airframe.
Enstrom Service Notes 0029 and 0029A pertain to this same subject.
This amendment becomes effective March 18, 1976.