AD 59-09-04

59-09-04 VERTOL: Applies to all Models 44A, B, and C Helicopters.

Compliance required as indicated, but no later than May 15, 1959.

(1) A failure of the low velocity fan disc assembly, P/N 42P6422, has recently been experienced in a Vertol 44 helicopter. The failure originated as a crack at the blade retaining bolt hole in the disc flange forward face, progressing radially into the flange and disc radius and continuing circumferentially in the radius area for 14 to 16 inches. This portion of the fan disc, containing six fan blades, then separated from the fan and was thrown through the left-hand side of the fuselage.

(2) To preclude recurrence of said failures, fan disc assemblies, P/N 42P6422, must be retired at 400 hours' time.

(3) It is permissible to operate the fan to 500 hours, providing the following requirements are complied with at, or before, 400 hours' time:

a. Remove spinner, P/N 42P6420.

b. Visually inspect the disc flange in the blade retaining bolt hole area for evidence of cracks.

c. Reassemble, adding AN 960-416 washers under the 32 nuts in place of removed spinner. (The spinner must not be reinstalled, to facilitate future inspections.)

d. Inspect the above-mentioned areas for evidence of cracks every four (4) flight-hours.

e. Any evidence of cracks will be cause for immediate retirement of the fan disc assembly. Fans removed from service because of cracks will be destroyed or mutilated so as to preclude the possibility of their being returned to service.

(Vertol Service Department Technical Memorandum No. 1901 covers this same subject.)