AD 98-12-30 Airworthiness Directives; McDonnell Douglas Helicopter Systems Model MD-900 Helicopters

Models named: MD-900. Read the applicability below — it usually turns on serial or part numbers too.

Model MD-900 helicopters, with main rotor upper hub assembly (hub assembly), part number (P/N) 900R2101006-101 or - 103, installed, certificated in any category. Note 1: This AD applies to each helicopter identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For helicopters that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must use the authority provided in paragraph (f) to request approval from the FAA. This approval may address either no action, if the current configuration eliminates the unsafe condition, or different actions necessary to address the unsafe condition described in this AD. Such a request should include an assessment of the effect of the changed configuration on the unsafe condition addressed by this AD. In no case does the presence of any modification, alteration, or repair remove any helicopter from the applicability of this AD.

Required as indicated, unless accomplished previously. To prevent failure of the hub assembly, loss of drive to the main rotor assembly, and subsequent loss of control of the helicopter, accomplish the following: (a) For a hub assembly that has accumulated 300 or more hours time-in-service (TIS), accomplish the inspection procedures in paragraph (b) of this AD before further flight. For a hub assembly that has accumulated less than 300 hours TIS, accomplish the inspection procedures in paragraph (b) of this AD within the next 25 hours TIS. (b) Inspect and reassemble the hub assembly as follows: (1) If present, remove sealant from the drive plate attachment to the main rotor assembly. (2) Using an indelible marker, number the main rotor drive plate attachment fastener torque sequence on the drive plate (Figure 1). BILLING CODE 4910-13-U [[Page 2812]] [GRAPHIC] [TIFF OMITTED] TR19JA99.014 BILLING CODE 4910-13-C [[Page 2813]] (3) Remove the main rotor drive plate assembly (drive plate assembly) and fretting buffer. Discard the 10 bolts and nuts and 20 washers. (4) Using paint stripper (C313 or equivalent) and cleaning solvent (C420 or equivalent), remove the paint from the upper mating surface of the hub assembly to enable an accurate visual inspection of the drive plate attachment bolt hole (bolt hole) area for cracking (Figure 1). Ensure the paint stripper and solvent DO NOT contaminate the upper bearing and upper grease seal areas. (5) Using a 10-power or higher magnifying glass, inspect the area around the 10 bolt holes of the hub assembly for cracks. If a crack is found, replace the hub assembly with an airworthy hub assembly. (6) Remove any fretting from the mating surfaces of the hub assembly and the drive plate assembly. Note 2: Boeing McDonnell Douglas Helicopter Systems Service Letter SL900-039, dated May 20, 1998, pertains to the subject of this AD. (7) Reinstall the main rotor drive plate using 10 new sets of replacement attachment hardware. Torque the nuts to 160-180 in.-lbs. above locknut locking/run-on torque in the sequence shown (Figure 1). Record in the rotorcraft log book the locknut locking/run-on torque for each nut. (c) After the next flight, verify that the torque on each of the 10 nuts is at least 160 in.-lbs. above the locknut locking/run-on torque (minimum torque). Re-torque as required without loosening nuts. Fillet surface seal main rotor drive plate to fretting buffer to hub assembly mating lines, and seal all exposed unpainted upper surfaces of the hub assembly. (d) Thereafter, at intervals of at least 4 hours TIS, not to exceed 6 hours TIS, verify that the torque of each of the 10 nuts is at least the minimum torque. Re-torque as required without loosening nuts. This torque verification is no longer required after the torque on each of the 10 nuts has stabilized at the minimum torque for each nut during two successive torque verifications. (e) Repeat the requirements specified in this AD at intervals not to exceed 150 hours TIS. Note 3: Rotorcraft Maintenance Manual, CSP-900RMM-2, Section 62- 20-00 and 63-10-00, pertain to the subject of this AD. (f) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Los Angeles Aircraft Certification Office, FAA. Operators shall submit their requests through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, Los Angeles Aircraft Certification Office. Note 4: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Los Angeles Aircraft Certification Office. (g) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the helicopter to a location where the requirements of this AD can be accomplished. (h) This amendment becomes effective on February 3, 1999, to all persons except those persons to whom it was made immediately effective by priority letter AD 98-12-30, issued June 4, 1998, which contained the requirements of this amendment. Issued in Fort Worth, Texas, on January 4, 1999. Henry A. Armstrong, Manager, Rotorcraft Directorate, Aircraft Certification Service. [FR Doc. 99-683 Filed 1-15-99; 8:45 am] BILLING CODE 4910-13-U