74-12-01 ENSTROM: Amendment 39-1856 as amended by Amendment 39-1940. Applies to Models F-28 and F-28A helicopters:
Compliance: Required as indicated, unless already accomplished.
To prevent failure of the forged idler yoke (P/N 28-13223)
(a) Before further flight and every 10 hours' time in service thereafter inspect by dye penetrant inspection method the webbed area of the forged idler yoke P/N 28-13223 for cracks. A forged idler yoke can be distinctively identified by the Part Number 28-13223 forged in 1/4 inch raised numbers on one side of the barrel portion and the alloy number MMT2014 forged in raised letters on the other side.
(b) As part of each pilot preflight inspection (logbook entry not required), the owner/operator is required to visually inspect the webbed area of the forged idler yoke P/N 28- 13223 for cracks.
(c) If cracks in the forged idler yoke P/N 28-13223 are detected when inspected in accordance with paragraph (a) or (b) above, replace it before further flight with a cast idler yoke P/N 28-13299, at which time the inspections required by this Airworthiness Directive are no longer applicable.
(d) The forged idler yoke P/N 28-13223 can be replaced at any time with a cast idler yoke P/N 28-13299 at which time inspections required by this Airworthiness Directive are no longer applicable.
(e) Equivalent methods of compliance with this Airworthiness Directive must be approved by the Chief, Engineering and Manufacturing Branch, Federal Aviation Administration, Great Lakes Region.
Amendment 39-1856 was effective June 5, 1974, and was effective April 19, 1974, for all recipients of the air mail letter dated April 19, 1974, which contained this amendment.
This Amendment 39-1940 becomes effective September 4, 1974.