AD 75-22-12 ACTIVE

75-22-12 SIKORSKY: Amendment 39-2400. Applies to Sikorsky model S-55 series helicopters incorporating AiResearch model TSE331-3U-303N engines per Supplemental Type Certificate (STC) SH125WE or SH127WE, certificated in all categories.

Compliance required as indicated.

To prevent possible inflight power loss accomplish the following:

A. Within the next 10 hours time in service after the effective date of this AD, unless already accomplished, and thereafter as required by subparagraph (8):

(1) Inspect and functionally test the fuel deceleration valve (AiResearch P/N 692545-400 or 868558-1) by disconnecting the fuel bypass line and capping off the line to prevent fuel leakage from the fuel pump. With the engine operating and the "AIR-GROUND" switch in the "GROUND" position, the deceleration bleed valve is to be cycled electrically open and closed using the decel button on the pilot's cyclic control stick to assure that no fuel leakage occurs when the valve is inthe normally closed position. Replace the valve if it does not function properly or leaks any fuel when closed. Remove cap and reconnect bypass line.

(2) Remove the tee fitting (AiRearch P/N 3101322-1) from the engine and visually inspect the orifice for blockage. Replace tee fitting if the orifice is restricted. Reinstall tee fitting to engine if found free of obstructions.

(3) With the engine operating at 100 percent engine speed and the "AIR- GROUND" switch in the "AIR" position, functionally test the manual fuel flow control valve (AiResearch P/N 868558-2) for proper operation by cycling this valve using the cyclic control switch. If the engine does not react normally by losing RPM and then recovering to 100 percent engine speed as the manual fuel flow control valve is closed and opened, remove and replace this valve and repeat this functional check.

(4) Visually inspect the wiring and electrical connections associated with the deceleration control switch toassure that there has been no chafing or other damage which could cause improper operation of the deceleration bleed valve or manual fuel flow control valve.

(5) Calibrate engine tachometer and engine tachometer generator as a pair against an accurate standard to within plus or minus 0.5% true reading.

(6) Inspect and adjust, as necessary, the underspeed governor adjustment in accordance with the FAA approved rotorcraft maintenance manual.

(7) Inspect and adjust, as necessary, the throttle linkage to insure that the throttle high RPM stop is set correctly with respect to the engine fuel control stop in accordance with the FAA approved rotorcraft maintenance manual.

(8) Repeat the calibrations and inspections of paragraphs (5), (6) and (7), above, at intervals not to exceed 500 hours time in service, or twelve months, whichever occurs earlier. The calibrations required in (5) must be repeated whenever a tachometer indicator or tachometer generator is replaced.B. Within the next 10 hours time in service after the effective date of this AD, unless already accomplished:

(1) Install the fuel enrichment valve system per AiResearch Service Bulletin TSE331-73-0045, dated August 25, 1975, or later FAA approved revisions, and Helitec Corporation Service Bulletin No. AS55-01-3, dated August 29, 1975; and

(2) Incorporate and comply with Aviation Specialties Company Sikorsky S- 55, S-55B, and S-55C FAA approved Rotorcraft Flight Manual (RFM) revision No. 6, dated August 29, 1975, or later FAA approved revisions.

NOTE 1: B(1) and (2) shall be performed simultaneously.

NOTE 2: Refer to AiResearch Service Bulletin TSE331-735004 dated July 16, 1973, and Aviation Specialties Service Bulletin AS55-01-1 dated July 6, 1973, for identification and location of related hardware.

C. Until the actions required by paragraph B. above are performed, the following operating limitations and flight limitations (Section I, RFM) shall apply.

(1) Before each takeoff with the collective full down and the rotor engaged, determine that the engine idles above 100.5% RPM with the high RPM stop.

(2) At takeoff power the engine speed must not be below 99% RPM.

(3) Avoid rapid collective increases under high power conditions.

D. After the effective date of this AD refer to the rotorcraft flight manual for the nominal specific gravity of approved fuel types (see Section II, Specific Gravity). Operating personnel shall assure that the engine fuel control specific gravity adjustment is set properly at all times for the type of fuel being used.

E. Equivalent procedures may be approved by the Chief, Aircraft Engineering Division, FAA Western Region, upon submission of adequate substantiating data.

F. Aircraft may be flown in accordance with FAR 21.197 to a base for performance of the inspections, maintenance, and modifications required by this AD, provided the operating limitations set forth in paragraph (c) are applied.

This amendment becomes effective October 31, 1975 for all persons except those to whom it was made effective by individual airmail letters, dated September 8, 1975 which contained this amendment.