AD 83-04-04

83-04-04 ENSTROM HELICOPTER CORPORATION: Amendment 39-4566. Applies to Enstrom Models F-28A and 280 helicopters certificated in all categories equipped with main rotor gearboxes (P/N 28-13101) having the following serial numbers:

2A, 3A, 6, 8, 9, 10, 12, 13, 14, 15, 20, 21, 25, 26, 28, 29, 30, 31, 32, 34, 35, 36, 38, 39, 40, 41, 42, 43, 44, 46, 47, 48, 49, 51, 53, 56, 70, 72, 73, 74, 75, 76, 77, 78, 86, 95, 100, 07, 012, 016, 017, 019, 020, 027, 032, 037, 050, 057, 060, 063, 067, 081, 082, 084, 085, 087, 088, 089, 093, 094, 097, 098, 099, 01-001-71, 01-073-69, 02-001-71, 02-02-71, 02-13-70, 03-001-72, 03-002-72, 04- 001-72, 05-001-72, 05-003-72, 06-001-72, 07-001-72, 07-002-72, 07-004-72, 07-005-72, 07-006- 72, 08-001-72, 08-002-72, 09-001-72, 09-001-73, 09-002-72, 09-01-69, 09-02-69, 09-04-69, 09- 06-69, 09-07-69, 10-001-72, 10-002-72, 11-001-72, 11-002-72, 12-001-72, 13-002-72, 13-003- 72, 13-004-73, 14-001-72, 14-002-72, 14-005-72, 14-006-72, 15-001-72, 15-002-72, 16-001-72,16-002-72, 17-001-72, 20-001-72, 21-001-72, 21-002-72, 21-003-72, 22-001-73, 23-001-73, 23- 003-73, 25-002-73, 26-001-73, 27-001-73, 27-002-73, 27-003-73, 27-004-73, 28-001-73, 28-003- 73, 30-001-73, 31-001-73, 31-002-73, 32-001-73, 32-002-73, 32-004-73, 32-006-73, 32-007-73, 33-001-73, 33-002-73, 33-003-73, 33-006-73, 33-007-73, 34-001-73, 34-002-73, 35-001-73, 35- 002-73, 35-003-73, 35-004-73, 36-001-73, 36-002-73, 36-003-73, 37-001-73, 37-003-73, 37-005- 73, 38-001-73, 39-001-73, 39-002-73, 40-001-73, 43-001-73, 43-002-73.

To prevent the possible loss of power to the main rotor, accomplish the following:

Within the next 25 hours' time in service from the effective date of this AD:

a. Drain the oil from the transmission, and remove the oil filter cap assembly.

b. Rotate the main rotor shaft until the core hole in the upper surface of ring gear carrier (P/N 28-13106) is aligned with the oil filler port. This may be ascertained by looking through the oil filler port.

c. If no hole can be observed in the bottom web of the ring gear carrier, the wall thickness of the carrier is satisfactory and the inspections of steps d., e., and f. do not apply.

d. If a hole can be observed in the bottom web of the ring gear carrier, the thickness of the lower web must be determined to establish airworthiness.

e. Inspection tool, T-0125, is provided with Enstrom Service Directive Bulletin 0017, Revision C. Insert this inspection tool through the oil filler port and core hole and determine the thickness of the ring gear carrier lower web as shown in Figure 1 of Enstrom Service Directive Bulletin 0017, Rev. C., or FAA approved equivalent.

NOTE: T-0125 IS A GO/NO-GO GAUGE. IF IT WILL FIT OR GO OVER THE LOWER WEB, THE WEB IS TOO THIN AND IS UNAIRWORTHY. IF IT WILL NOT FIT OR GO OVER THE LOWER WEB, THE WEB IS SUFFICIENTLY THICK, AND IS AIRWORTHY.

f. Repeat steps b., d., and e. for each of the three holes in the ring gear carrier's lower web. If inspection tool T-0125 will slip over the web in any one of the three (3) lower web hole locations, the ring gear carrier is unairworthy.

g. Replace unairworthy ring gear carriers with new or serviceable ring gear carrier P/N 28-13106, Revision F, or later revision.

h. Service the transmission with oil in accordance with the Maintenance Manual and reinstall the oil filler cap assembly.

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

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

This supersedes Amendment 39-1794, as amended by Amendments 39-1850 and 39- 1922 (AD 74-05-03). This amendment becomes effective March 1, 1983.