AD 97-20-09 PL

97-20-09 CALIFORNIA DEPARTMENT OF FORESTRY; FIREFLY AVIATION HELICOPTER SERVICES (PREVIOUSLY ERICKSON AIR CRANE CO.); GARLICK HELICOPTERS, INC.; HAWKINS AND POWERS AVIATION INC.; INTERNATIONAL HELICOPTERS, INC.; RANGER HELICOPTER SERVICES; ROBINSON AIRCRANE; SCOTT PAPER CO.; SMITH HELICOPTERS; SOUTHERN HELICOPTER; SOUTHWEST FLORIDA AVIATION; WESTERN INTERNATIONAL AVIATION, INC.; UNC HELICOPTERS; AND U.S. HELICOPTER, INC.: Priority Letter issued on September 17, 1997. Docket No. 97-SW-35-AD.

Applicability: Model HH-1K (Type Certificate Data Sheet (TCDS) H5NM), TH-lF (TCDS H12NM, and R00008AT), TH-1L (TCDS H5NM, H7SO, and H4NM), UH-1A (TCDS H3SO), UH-1B (TCDS H1RM, H3NM, H13WE, H3SO, H5SO, and R00012AT), UH-1E (TCDS H5NM, H7SO, H8NM, and H4NM), UH-1F (TCDS H2NM, H7NE, H11SW, H12NM, and R00008AT), UH-1H (TCDS H13WE, H3SO, and H15NM), UH-lL (TCDS H5NM, H7SO, and H4NM), UH-1P (TCDS H12NM, and R00008AT), and SW204 (TCDS H6SO), SW204HP (TCDS H6SO), SW205 (TCDS H6SO), helicopters, with tailboom vertical fin spar, part number (P/N) 205-032-899, 205-030-846, or 205-032-851, all dash numbers, 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 (c) 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 repairremove any helicopter from the applicability of this AD.

Compliance: Required as indicated, unless accomplished previously.

To prevent in-flight failure of the tailboom vertical fin spar (vertical fin spar) and subsequent loss of control of the helicopter, accomplish the following:

(a) Within 8 hours time-in-service (TIS) after the effective date of this AD, modify the vertical fin spar as follows:

(1) Remove the 42 gearbox cover and open the drive shaft cover on the vertical fin spar assembly (see Figure 1).

(2) Remove the first four rivets from the fin spar located at the bottom of the vertical fin spar left-hand side at the tailboom and vertical fin spar junction, and the first four rivets aft of the junction along the lower edge of the vertical fin spar side-skin as shown (see Figure 2). CAUTION: Extreme care must be taken when drilling and removing rivets from the side of vertical fin spar to ensure the vertical fin spar assembly is not damaged.

(3) Trim the vertical fin spar left-hand side-skin using extreme care to not damage the vertical fin spar assembly (see Figure 3).

(4) Deburr the rivet holes and trimmed side-skin edges. Remove all debris. In a ventilated work area, remove any surface contaminants with a cloth that has been dampened with aliphatic naphtha or an equivalent cleaning solvent.

(5) Reattach the side-skin to the vertical fin spar using MS 20470AD rivets. DO NOT install the bottom two rivets into the vertical fin spar where the side-skin was trimmed.

(6) Attach the vertical fin spar side-skin lower edge using the rivets specified in Figure 2.

(7) Refinish all reworked areas.

(b) After modifying the vertical fin spar assembly, immediately inspect the vertical fin spar, and thereafter, inspect at intervals not to exceed 8 hours TIS, for cracks as follows:

(1) Remove the lower aft tailboom inspection door, located at tailboom station 180 (see Figure 4).

(2) Remove the 42 gearbox cover and open the drive shaft cover on the vertical fin (see Figure 1).

(3) Through the lower aft tailboom inspection door, using a bright light and an inspection mirror, inspect the vertical fin spar assembly adjacent to the tailboom top skin on the forward side, paying special attention to the left-hand edge and the adjacent surfaces (see Figure 2).

(4) In a ventilated work area, clean all surfaces to be inspected with a cloth dampened with aliphatic naphtha or an equivalent cleaning solvent. Using a bright light and a 10x magnifying glass, inspect the vertical fin spar assembly adjacent to the tailboom top-skin on the in-board and out-board sides, the vertical edge, and the two open rivet holes. Using a bright light and a mirror, inspect the aft side of the vertical fin spar in the same area. Special attention must be given to the left-hand edge of the vertical fin spar and any adjacent surfaces between fin station 66.31 and 71.31 (see Figure 2).

(5) If any crack is discovered on the vertical fin spar, replace the vertical fin spar assembly with an airworthy vertical fin spar assembly before further flight.

(c) 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, Rotorcraft 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, Rotorcraft Certification Office.

NOTE 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Rotorcraft Certification Office.

(d) 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.

(e) Priority Letter AD 97-20-09, issued September 17, 1997, becomes effective upon receipt.