88-11-06 THE ENSTROM HELICOPTER CORPORATION: Amendment 39-5920. Applies to Enstrom Model F28 series helicopters, certificated in any category, equipped with horizontal stabilizer center spar, P/N 28-11222 (Airworthiness Docket 88-ASW-5).
Compliance is required as indicated, unless already accomplished.
To detect cracks in the horizontal stabilizer attachments thereby preventing possible failure which could result in loss of control of the helicopter, accomplish the following:
(a) Prior to the first flight of each day after the effective date of this AD, conduct the following--
(1) Check both the left and right stabilizer security by applying a light up and down load at the tip of the stabilizer (i.e., approximately 3 lbs.);
(2) Check for deflection and/or looseness; and
(3) If a stabilizer deflects or is loose, comply with paragraph (b)(1) through (b)(10) of this AD, before next flight.
NOTE: The checks may be performed by the pilot andmust be recorded in accordance with FAR 43.9.
(b) Within the next 10 hours' time in service after the effective date of this AD, and thereafter at intervals not to exceed 100 hours' time in service from the last inspection, accomplish the following:
(1) Remove the left and right stabilizer assemblies P/N 28-20100, from the center spar, P/N 28-11222. Remove the inspection panel on the left side of the tailcone. Remove the bolts securing the spar to the tailcone and remove the spar from the tailcone.
NOTE: Mark spar position left, right, top, etc., prior to removal so that on reinstallation the spar will be repositioned correctly.
(2) Visually inspect the attachment fittings for burrs, fretting, or cracks.
NOTE: Particular attention should be directed to the spar attachment area around all drilled holes.
(3) Replace cracked fittings before next flight. Repair cracked sheet per standard practice, or replace with airworthy parts before next flight.(4) Measure the center spar wall thickness one time. Replace any center spar having a wall thickness less than 0.044 inch with an airworthy spar and comply with paragraph (b)(8) of this AD prior to the next flight.
(5) If the center spar thickness is 0.044 inch or greater, inspect the spar for cracks using a magnetic particle or dye penetrant inspection method and a 10-power or higher magnifying glass.
NOTE: Particular attention should be directed to the spar area around all drilled holes and if a crack is found, replace the spar with an airworthy part before next flight.
(6) Inspect the stabilizer spar trailing edge attachment clips, P/N 28- 20106, for cracks using a dye penetrant inspection or a visual inspection using a 10-power or higher magnifying glass. If a crack is found, replace the clip with an airworthy part before next flight.
(7) Inspect the center spar (particularly in areas of dissimilar metal contact) for corrosion. A spar with corrosion depth greater than 0.005 inch must be replaced before next flight. Surface corrosion may be removed with 320 grit emery paper. Protect bare areas using a light coat of epoxy primer (DeSoto 593X300 or equivalent).
(8) Install the center spar in its proper relative position to the tail cone. Whenever a new spar is installed, it must be match-drilled to the tailcone and stabilizers for proper incidence. Remove, deburr all holes, and protect all bare surfaces with epoxy primer prior to final assembly.
(9) Install the horizontal stabilizer using airworthy parts.
NOTE: A light coat of lubricant (LPS 500 or equivalent) on the outside of the spar and the inside of the fittings will aid in assembly.
(10) Record the rotorcraft's weight and balance change as appropriate.
NOTE: Changing from a 0.035-inch to a 0.049-inch nominal wall thickness center spar causes a weight increase of 0.37 lb. at longitudinal station 270.0.
(c) 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, Federal Aviation Administration, 2300 E. Devon Ave., Des Plaines, IL. 60018.
NOTE: Enstrom Service Bulletin No. 0076, dated December 15, 1987, pertains to this AD.
This amendment 39-5920 supersedes AD 72-04-04, Amendment 39-1395, as amended by Amendment 39-2884.
This amendment 39-5920 becomes effective May 31, 1988.