AD 75-22-01

75-22-01 ENSTROM: Amendment 39-2384 as amended by Amendment 39-2651. Applies to Enstrom Model F-28A helicopters certificated in all categories, as indicated in the following tables:

Table I - Improper Machining of the Tapered Bore of Main Rotor Spindle P/N 28- 14282.

Helicopter S/N's 203, 205, 209, 216, 220, 221, 223, 224, 225, 227, 231, 232, 233, 235, 236, 237, 240 and all other helicopters which received replacement main rotor spindles between June 18, 1974 and October 1, 1974 inclusive.

Table II - Bore of Main Rotor Spindle P/N 28-14282 Machined Too Deep.

Helicopter S/N's 116, 117, 160, 177, 178, 179, 184, 185, 187, 188, 189, 190, 192, 193, 194, 195, 196, 197, 198, 201, 204, and 217.

Compliance required as indicated unless already accomplished.

To detect main rotor spindles with machining deficiencies accomplish the following:

(a) Within the next 100 hours time in service after the effective date of this Airworthiness Directive, inspect all helicopters listed in Table I above for improper machining of the tapered spindle bore in accordance with the information contained in Enstrom Service Note No. 0020A dated August 11, 1975, or an equivalent procedure approved by the Chief, Engineering and Manufacturing Branch, Great Lakes Region. All spindles that have been machined with a straight internal bore shall be identified in the log book as a life limited spindle. (See paragraph (c) for retirement life of these spindles.)

(b) Within the next 100 hours time in service after the effective date of this Airworthiness Directive, inspect all helicopter main rotor spindles listed in Table II above for an excessive bore depth in accordance with the information contained in Enstrom Service Note 0021B dated, August 11, 1975, or an equivalent procedure approved by the Chief, Engineering and Manufacturing Branch, Great Lakes Region. All spindles that have been machined with an improper bore depth shall be identified in the log bookas life limited spindles. (See paragraph (c) for the retirement life of these spindles.)

(c) Main rotor spindles which have machining deficiencies indicated in paragraphs (a) and (b) above are considered to be life limited parts and must be replaced with a new part of the same part number no later than at 4,500 hours total time in service and the life depleted part is to be rendered unserviceable. Spindles which are determined to be machined correctly may be returned to service and do not have a life limit imposed on them.

Amendment 39-2384 became effective October 20, 1975. This amendment becomes effective July 1, 1976.