75-15-02 HUGHES HELICOPTERS: Amendment 39-2259. Applies to all Hughes Model 269A, 269A-1, and 269B helicopters, certificated in all categories, and military TH-55A helicopters, as indicated herein.
Compliance required as indicated.
To prevent possible loss of control of the throttle and loss of control of engine power due to cracking and separation of aluminum throttle gear sector, P/N 269A7223 (Basic), with nominal 129 degrees of teeth, accomplish the following:
(A) Within 25 hours additional time in service, after the effective date this AD, unless already accomplished:
(1) Gain access to the throttle sector gears in the collective sticks at the lower throttle control housings and inspect through the housing cover plates, or by equivalent means, to determine if the gear sectors are steel or aluminum. Observe the nominal included angle of the aluminum gear sector teeth.
NOTE: The manufacturer has identified three types of throttle gear sectors in the Hughes 269 helicopter which are unidentified by part number on the helicopter. The three gear sectors can be identified as follows:
(a) The P/N 269A7223-3 gear sector is a steel bevel gear having a nominal included angle between the gear teeth of 304 degrees. The gear has a pre-drilled hole approximately .05 inches minimum distance from the boss end to accept a spring pin (roll pin) and a cotter pin for assembly with the mating left hand or right hand factory pre-drilled aluminum shaft.
(b) A P/N 269A7223 (Basic) gear sector is identical to the -3 gear, except the gear has been fabricated from aluminum and has a nominal included sector angle between the gear teeth of 304 degrees.
(c) A P/N 269A7223 (Basic) gear sector is an aluminum gear having a nominal included angle between the gear teeth of 129 degrees and has a pre-drilled hole approximately .05 inches minimum distance from the boss end to accept a roll pin and cotter pin during assembly with the mating left handor right hand factory pre-drilled aluminum shaft.
(2) Remove the left hand (applicable to dual controls) and right hand aluminum gear sector assemblies (throttle sector gearshaft assemblies) from the helicopter which have an included angle between the gear sector teeth of 129 degrees and identify the gear sector portion per paragraph (A)(7).
(3) Install new steel type throttle gearshaft assemblies having the following part numbers: P/N 269A7707-3(L.H.) or P/N 269A7707-7(L.H.) in the left throttle housing position and a P/N 269A7269-3(R.H.) in the right throttle housing position.
(4) If the preceding part number throttle gearshaft assemblies cannot be procured from the manufacturer for compliance with this AD, accomplish the installation required in paragraph (A)(3) in accordance with the following procedure:
(a) Procure a new P/N 269A7223-3 steel gear sector. (If a P/N 269A7223-3 steel gear sector cannot be procured from the manufacturer, only because of lackof availability of this part, the P/N 269A7223 (Basic) aluminum gear sector which has 304 degrees included angle between the gear sector teeth may be used as no service problems pertaining to cracking with this gear sector have been reported.)
(b) Remove the P/N 269A7223 (Basic) aluminum gear sector having an included angle between the gear teeth of 129 degrees from the mating aluminum shaft by removing the cotter pin and the roll pin. The aluminum shaft is comprised of two different part number shafts, differing essentially in length. The P/N 269A7708(L.H.) shaft is located in the left throttle housing for dual control helicopters and a P/N 269A7271(R.H.) shaft is located on the right throttle housing.
(c) Using a magnifying glass having at least 10X power, perform a close visual inspection of the shaft hole for cracks, corrosion, wear, scoring, hole elongation at the inside hole diameter which accepts the roll pin, or other defects.
(d) Measure and record the left hand (if applicable) and right hand shaft hole inside diameter which accepts the roll pin. The acceptable dimensions for the inside hole diameter are .156 inches to .160 inches.
(e) Measure and record the shaft outside diameter. The acceptable dimensions for the outside diameter of the left hand and right hand shaft are .6240 inches to .6250 inches.
(f) Measure and record the existing inside diameter of the hole in the P/N 269A7223-3 steel sector gears and confirm that it measures .156 inches to .160 inches.
(g) If the existing shaft and new sector gear are found acceptable, install the P/N 269A7223-3 steel gear sector on the mating aluminum shaft. Assure that the center line of the hole in the gear and the center line of the hole in the shaft are in accurate alignment. While maintaining alignment, press the P/N NAS561-5-14 roll pin through the gear and shaft hole with the chamfered end of the roll pin in the starting position and secure with a P/N AN381-3-20 cotter key. Seal with zinc chromate primer. If excessive force is required to press the roll pin in place, misalignment between the holes may have occurred and will require re-inspection for possible damage to the aluminum shaft hole. Tapering the roll pin beyond the existing chamfered end to allow for easy insertion of the roll pin is unacceptable.
NOTE: The manufacturer has introduced a two piece optional roll pin configuration into production for the left hand throttle gearshaft assembly to improve the procedures for adjusting the AN932-2 pipe plug. Field fabrication of this dual roll pin design is not permissible in the field unless procedures are approved by the Chief, Aircraft Engineering Division, FAA Western Region.
(h) Identify by ink stamping the letter "A" on the outer gear sector diameter of the gears.
(i) Any shafts in stock which have not been pre-drilled by Hughes Helicopters may not be installed. Drilling of shafts in the field is not permissible unless special equipment and procedures are approved by the Chief, Aircraft Engineering Division, FAA Western Region.
(5) Inspect on a one-time basis, those gear sectors which have been field assembled per paragraph (A)(4), after the accumulation of 250 hours additional time in service and before accumulating 300 hours additional time in service per the following procedures:
Inspect the gearshaft assemblies for corrosion or other defects and determine if radial or axial play exists between the gear and the shaft. If any perceptible play exists, the shaft hole may be elongated or other defects may exist which will require disassembly of the gear from the shaft and inspection per paragraph (A)(4) or replacement per paragraph (A)(3).
(6) Record inspections and modifications by paragraph numbers in compliance with this AD in the Aircraft Maintenance Records in accordance with FAR 91.173.
(7) Identify in a conspicuous manner that the part is not serviceable to prevent inadvertent return to service, those throttle gear sectors, shafts, or throttle gearshaft assemblies that have been removed from service due to the provisions of this AD.
(8) For additional procedures concerning removal, installation and inspection of throttle gearshaft assemblies refer to Hughes Model 269 Series Helicopter Basic Handbook of Maintenance Instructions, issued April 1, 1974, Revision No. 2, January 1974, or later revisions. Operators are cautioned to carefully observe the following manual requirements:
(a) Proper shimming between the gear sector and shaft bearing to stay within allowable backlash limits.
(b) Proper fit and seating of the bearings against the bore shoulder and proper application of loctite.
(c) Proper determination that gears do not bind and checking for damage if binding occurs.
(d) Proper tightening of the pipe plug for a push fit with zero play between rod and gearshaft.
(e) Proper alighment of heel edge of the gear teeth on the sector gear and the pinion.
(f) Proper rigging of the gear sector position in relation to the throttle pinion and the pilot's throttle grip.
(B) Within 25 hours additional time in service, after the effective date of this AD, unless already accomplished, operators of:
(1) Helicopters which, as of the effective date of this AD, have had the factory installed aluminum throttle gear sectors replaced with either steel or aluminum gear sectors as replacements; or
(2) Helicopters which, as of the effective date of this AD, incorporate throttle gearshaft assemblies of any type which were assembled in the field with shafts drilled at other than the Hughes production facility; shall perform the inspections and replacements described in paragraphs (A)(3) through (A)(8), above.
(C) Equivalent inspection and modification procedures for the throttle gear sector, shaft and gearshaft assembly may be approved by the Chief, Aircraft Engineering Division, FAA Western Region.
(D) Aircraft may be operated to a base for accomplishment of that maintenance required by this AD, per FAR's 21.197 and 21.199.
This amendment becomes effective July 15, 1975.