56-20-05 DOUGLAS: Applies to All DC3 Series, DC-4 and C54-DC Series Aircraft Powered With Pratt & Whitney Military R-2000 and Twin Wasp D Series Engines. \n\n\tCompliance required not later than December 1, 1956. \n\n\tTo avoid crankshaft bending failures, the following placard must be placed on the instrument panel in a conspicuous place: "Avoid Continuous Operation of the Engines between 2310 and 2510 r.p.m." The tachometers must be marked with a red radial band in the above range. \n\n\tThis supersedes AD 48-03-01, which applied only to DC-4 airplanes.