AD 82-16-09

82-16-09 ENSTROM HELICOPTER CORPORATION: Amendment 39-4429. Applies to all Model F-28A, F-28C, F-28C, F-28F, 280, 280C, and 280F helicopters certificated in all categories.

Compliance required as indicated unless already accomplished. To detect wear damage and to prevent possible failure of the main rotor blade grips, accomplish the following:

Within the next 100 hours' time in service from the effective date of this AD and thereafter at intervals not to exceed 200 hours' time in service from the last inspection:

(a) Remove the main rotor blades per instructions in Section 6 of the maintenance manual.

CAUTION: To prevent damage to the Lamiflex bearing, it is important to comply with blade grip placard cautioning against over-rotation of the grip when the pitch link is disconnected.

(b) Remove Lamiflex thrust bearing cover assembly (P/N 28-14239).

(c) Remove any dirt, grease, or other abrasive material from the space around the Lamiflex thrust bearing.

(d) Inspect shim(s) (P/N 28-14293) for alignment/concentricity and clearance.

(1) The shim(s) must be concentric with the Lamiflex thrust bearing.

(2) Ascertain that the shim(s) do not protrude beyond the outer diameter of the Lamiflex bearing.

(e) Inspect blade grip (P/N 28-14279) inner faces for possible wear grooves.

(f) If there is shim misalignment, inadequate clearance, or wear grooves in grips, remove: cotter pin (P/N AN 380-4-8), retention nut (P/N 28-14335), shim(s) (P/N 28-14293), and Lamiflex thrust bearing (P/N 28-14310).

(g) Inspect blade grips having wear grooves to establish repairability. Grips having a wear-groove depth greater than .125 inch must be replaced. Grips having a wear-groove depth of .125 inch or less are repairable.

(h) Repair blade grips(s) by blending out groove(s) smoothly over a circular area having a diameter equal to the wear-groove length. Do not remove excessive material such that the resultant concave blended surface extends beyond the Lamiflex thrust bearing cover (P/N 28- 14239) allowing it to leak.

NOTE: To perform this blending operation, it may be necessary to remove the grip from the main rotor retention assembly. Remove the grip(s) per instructions in Section 6 of the maintenance manual.

(i) Inspect shim(s) for serviceability. Discard any shim that is deformed out-of- round, has a nonuniform thickness, or was removed from an assembly where grip wear grooves were discovered.

(j) Replace discarded shim(s) with new shim(s) of the same nominal thickness.

(k) Reassemble main rotor retention assembly and main rotor assembly in accordance with the instructions in Section 6 of the maintenance manual.

(l) Any equivalent method of compliance with this AD must be approved by the Chief, Chicago Aircraft Certification Office, Federal Aviation Administration, 2300 Devon Avenue, Des Plaines, Illinois 60018.

(m) In accordance with FAR 21.197, flight is permitted to a base where the inspection required by this AD may be accomplished.

This amendment becomes effective August 4, 1982.