AD 75-22-10

75-22-10 ENSTROM: Amendment 39-2403. Applies to Enstrom Models F-28A and 280 helicopters certified in all categories, with the following serial numbers:

F-28A - S/N's 4 through 275, 277, 278, 280 through 283. 280 - S/N's 1001 through 1006.

Note: Helicopters equipped with a 'tang' hub lock washer, Enstrom P/N 28-14263, are exempt from compliance with this Airworthiness Directive.

Compliance required as indicated unless already accomplished.

Within the next 25 hours time in service after the effective date of this Airworthiness Directive:

(a) Remove the main rotor retention nut, Enstrom P/N 28-14004, and hub nut washer, Enstrom P/N 28-14005;

(b) Replace hub nut washer, Enstrom P/N 28-14005, with a new retention washer, Enstrom P/N 28-14008, or an equivalent approved by the Chief, FAA Engineering and Manufacturing Branch, Great Lakes Region. The chamfer on the new washer must be installed parallel with the main rotor spline chamfer; and,

(c) Install main rotor hub retention nut, Enstrom P/N 28-14004, and torque nut to a value of 400 ft. lbs. Re-safety with .040" diameter stainless steel safety wire in three (3) places to the hub adapter plate bolt heads.

Enstrom Service Notes 0025 and 0025A pertain to this same subject.

This amendment becomes effective October 28, 1975.