53-20-01 MARTIN: Applies to All Models 202 and 202A Airplanes With Hamilton Standard Reversing Propeller Installations In Which the Reverse Feature is Not Used, and In Which the Normal Reverse Pitch Stop Ring Has Been Relocated to Act Essentially as a Low Pitch Stop.
Compliance required as indicated.
With the reverse pitch stop ring relocated to act as a low pitch stop, and with inadvertent energization of the reverse solenoid valve, the stop ring will fail under the extreme loads resulting from high oil pressure surge plus the high blade twisting moments attendant to rapid pitch change toward low pitch. This failure will result in the jamming of the pitch changing mechanism, or an inadvertent propeller reversal. To preclude any hazardous incidents, modification of the internal mechanism of the propeller dome, or modification of the propeller control system is necessary. Accomplish items I, II, and III.
I. Comply with AD 52-15-02.
A. Item I of AD 52-15-02 isto be accomplished by means of a progressive modification program to be submitted to and approved by the FAA. The program shall begin no later than November 1, 1953, and shall be completed no later than August 1, 1954.
B. Item III shall be instituted when reversing is reactivated.
II. Modify the internal mechanism of the propeller dome. The modifications include removal of the normal low pitch stops, and incorporation of a dump valve which opens just above the normal low pitch position to maintain oil pressure of 50 to 100 p.s.i. on the decrease pitch side of the piston.
A. Replace the present oil transfer housing 70451 or 77828 with engine shaft extension assembly 70300.
B. Remove the present low pitch stop lever assembly 71042, 71676 or 76149 from the propeller entirely.
C. Replace the present piston sleeve 68425 with a new piston sleeve 72259 and snap ring 67698. Since the piston sleeve is pressed into the piston, the internal diameter of the sleevemust be machined after assembly.
D. Purchase Orders for the above parts must be submitted to Hamilton Standard by November 1, 1953.
E. Hamilton Standard Service Bulletin No. 264 covers this same subject.
F. Compliance required prior to November 1, 1954.
III. Modify the propeller control system.
A. At the A or unfeathering relays in the propeller relay control box, disconnect the wires that run through the nose junction box and into the reversing control boxes (Hamilton Standard P/N 72400) to connect the A relays with the throttle microswitches.
(1) Either physically remove the full run of these wires from the A relay terminal to the nose junction box terminal strip, or
(2) Physically remove the portion from the A relays to the pin connector in the propeller control relay box, and disconnect these wires from the mating pin in the external portion of the pin connector. Insulate the exposed ends of these wires, and secure them from movement in such manner as to preclude their becoming grounded or contacting any terminals.
B. Modify the reverse solenoid circuit wiring from the reverse solenoids to the terminal on the A relays by providing continuous wires physically isolated from all other circuits.
C. Comply with item I.C. of AD 52-15-02.
D. Revise the reversing solenoid circuits to comply with Hamilton Standard Service Bulletin No. 236, Ref. 955.
E. Provide positive mechanical stops for both throttle levers so they cannot be moved into the reverse range.
(1) Item 2, of NWA Mechanical Order No. 479, dated November 21, 1950, is considered acceptable to accomplish this.
(2) Comply with items 3 and 4 of NWA Mechanical Order No. 479, dated November 21, 1950.
F. Items III.A, B, C, D, and E of AD 53-20-01 are to be accomplished by April 1, 1954.
G. No later than November 1, 1953, all operating instructions regarding unfeathering procedures shall specify that the following practicesare to be observed, and shall indicate that the reason is to guard against jamming the pitch changing mechanism or possible inadvertent reversal during the unfeathering operation:
(1) If unfeathering is being accomplished at night the wing illumination lights or landing lights are to be used to permit observation of propeller operation.
(2) The propeller is to be watched during unfeathering and the button is to be released when rotation starts. (This should normally be in 1 or 2 seconds.)
(3) The tachometer is not to be used as a guide for determining when unfeathering is to be terminated.