AD 62-26-01

62-26-01 DOUGLAS: Amdt. 517 Part 507 Federal Register December 8, 1962. Applies to All C54-DC Series and DC-4 Aircraft Equipped With Pratt & Whitney Aircraft Twin Wasp Series and R-2000 Series Engines and Hamilton Standard 23E50/6507-0 Propellers.

Compliance required within the next 200 hours' time in service after the effective date of this AD.

Recent resurveys of 23E50/6507-0 propeller blade vibration stresses have shown that vibration stresses in excess of allowable limits for continuous safe operation occur over a wider range of engine operating speeds than was determined by previous surveys. To prevent possible blade failures due to exceeding allowable stress limits within this speed range, the following is required:

(a) Remove the existing placard covering the 1,600 to 1,700 r.p.m. range and install a new placard in full view of the pilot to read:

"During flight, avoid operation between 1,550 and 1,750 r.p.m. During ground running, avoid operation between 1,550 and 1,800 r.p.m. when the blades are off the low pitch stops."

(b) Mark the tachometers with a red arc over the 1,550 and 1,750 r.p.m. range.

(c) Revise the operating limitations section of the FAA approved Airplane Flight Manual to incorporate the limitations in (a) and (b).

NOTE: The other restricted operating speed range between 2,310 and 2,510 r.p.m. required by AD 56-20-05 still remains in effect. For the purpose of this directive, a single placard reading: "During flight, avoid operation between 1,550 and 1,750 r.p.m. and between 2,310 and 2,510 r.p.m.", in the first sentence, may be installed if desired. Similar wording may be used for the FAA approved Airplane Flight Manual.

This directive effective January 8, 1963.