AD 90-01-06

90-01-06 ENSTROM HELICOPTER CORPORATION: Amendment 39-6457. Docket No. 89-ASW-59. Applicability: Enstrom Model F-28, F-28A, F-28C, F-28C-2, F-28F, 280, 280C, 280F and 280FX Series Helicopters, equipped with tail rotor gearboxes, P/N 28-13500-1, 28-13525-1, -3, and -5, containing spiral miter gear-set "Boston Gear XR-137-2YR" and "Boston Gear XR- 137-2YL."

Compliance: Required as indicated, unless already accomplished.

To prevent the loss of tail rotor thrust and directional control, which could result in loss of the helicopter, accomplish the following:

(a) Within the next five hours' time in service--

(1) Determine from the aircraft log book if tail rotor gearbox, P/N 28-13500- 1, 28-13525-1, -3, or -5, is installed in the helicopter;

(2) Remove all -1, -3 or -5 tail rotor gearboxes containing spiral miter gear- set "Boston Gear XR-137-2YR" and "Boston Gear XR-137-2YL", with 1,200 or more hours' time in service since the last overhaul, and replace with an airworthy gearbox; and

(3) For tail rotor gearboxes with less than 1,200-hours' time in service since the last overhaul, remove the magnetic chip detector (plug), drain the oil from the tail rotor gearbox, filter the oil using a white filter paper, and inspect the magnetic plug and the filter paper with a ten-power magnifying glass--

(i) If no metal contaminants are found, return the tail rotor gearbox to service;

(ii) If the inspection required by paragraph (a)(3) above reveals the presence of more than 15 thin metal flakes, splinters, or granular-shaped steel particles greater than 0.005-inches thick or longer than 0.015 inches, remove and replace the tail rotor gearbox with an airworthy gearbox; and

(iii) If metal contaminants are found that are fewer in number and smaller than those described in paragraph (ii) above, conduct further servicing and inspection in accordance with paragraph (a)(4).

(4) Flush the gearbox with clean oil and clean the magnetic plug with a cotton swab and/or an air gun.

NOTE: Do not clean the magnetic plug with a strong magnet. This weakens the magnet on the chip detector.

(i) Refill the tail rotor gearbox with Mil-L-6082B Shell SAE10W, Mil-L-6082B Texaco SAE 10W, or Mil-L-22851B Phillips SAE 20W-50W lubricant. If any of these lubricants are not available, consult Enstrom Helicopter Corporation, Customer Service Department, for a possible alternative.

(ii) Conduct a serviceability check by flying the helicopter for one hour at various power settings up to full power, and then repeat the inspection required by paragraphs (a)(3) above.

(A) If no metal contaminants are found, return the tail rotor gearbox to service.

(B) If the repeat inspection reveals the presence of any metal contaminants, regardless of size or number, remove and replace the tail rotor gearbox with an airworthy gearbox.

(b) At intervals not to exceed 100 hours' time in service on all gearboxes returned to service after passing the inspections of paragraph (a), remove the magnetic chip detector (plug), drain the oil from the tail rotor gearbox, filter the oil using a white filter paper, and inspect the magnetic plug and the filter paper with a ten-power magnifying glass.

(1) If the inspection reveals the presence of any metal contaminants, regardless of size or number, remove and replace the tail rotor gearbox with an airworthy gearbox.

(2) If no metal contaminants are found return the tail rotor gearbox to service.

(c) Within 1,200 hours' time in service since the last overhaul, remove and replace the tail rotor gearbox with an airworthy gearbox.

(d) An alternate method of compliance with this AD, which provides an equivalent level of safety, may be used when approved by the Manager, Chicago Aircraft Certification Office, FAA, 2300 East Devon Avenue, Room 232, Des Plaines, Illinois 60018.

(e) In accordance with Sections 21.197 and 21.199,flight is permitted to a base where the maintenance required by this AD may be accomplished.

This amendment (39-6457, AD 90-01-06) becomes effective on February 1, 1990.