84-02-05 BOEING: Amendment 39-4798. Applies to Boeing Model 747 series airplanes certificated in all categories. Compliance required as indicated, unless already accomplished. \n\n\tA.\tTo clarify the operation of the anti-icing system, emphasize the need to maintain the specified minimum N1 engine rpm during icing conditions, and expand the definition of icing conditions, accomplish the following: Within 120 days from the effective date of this AD, unless already accomplished, revise the FAA approved Airplane Flight Manual (AFM) CERTIFICATE LIMITATIONS SECTION by adding: \n\n\t\t\t\t"ENGINE ANTI-ICE SYSTEM \n\n\tWhen penetrating or operating in Icing Conditions, maintain a minimum of 50 percent N1 rpm at 10,000 feet and above, and 45 percent N1 rpm for Pratt & Whitney JT9D and General Electric CF6 engines, and 42 percent N1 for Rolls Royce RB211 engines, below 10,000 feet altitude, except as required for landing. \n\n\tNacelle anti-ice must be ON during all ground and flight operationswhen icing conditions exist or are anticipated, except during climb and cruise when the temperature is below -40 degrees C SAT. Nacelle anti-ice must be ON prior to and during descent in all icing conditions, including temperatures below -40 degrees C SAT. \n\n\t\tNOTE: Icing Conditions - Icing Conditions exist when the OAT on the ground and for takeoff, or TAT inflight is 10 degrees C or below and visible moisture in any form is present (such as clouds, fog with visibility of one mile or less, rain, snow, sleet, and ice crystals). \n\n\tIcing conditions also exist when the OAT on the ground and for takeoff is 10 degrees C or below when operating on ramps, taxiways or runways where surface snow, ice, standing water, or slush may be ingested by the engines or freeze on engines, nacelles or engine sensor probes." \n\n\tB.\tTo alert the flight crew of engine operation at a lower N1 than required for icing condition, install a LOW N1 rpm caution indication system as follows: \n\n\t\tWithin 24 months from the effective date of this AD, unless already accomplished, provide "LOW N1" indication that will alert the flight crew that the nacelle anti-ice is "ON and N1 is less than 45 percent N1 (42 percent N1 for RB211 engines) below 10,000 feet, and is less than 50 percent N1 above 10,000 feet altitude. \n\n\t\tNOTE: The LOW N1 indication may be provided by incorporating Boeing Service Bulletin S/B 747-77-2060 for the JT9D Pratt & Whitney powered airplanes and S/B 747-77-2063 for General Electric CF6 and Rolls Royce RB211 powered airplanes. \n\n\t\tBoth service bulletins have been approved by the FAA and were released on February 14, 1983. The service bulletins may be obtained from the Boeing Company at the following address: The Boeing Company, P.O. Box 3707, Seattle, Washington 98124. \n\n\tC.\tAlternate means of compliance with the AD which provide an equivalent level of safety may be used when approved by the Manager, Seattle Aircraft Certification Office, FAA, 9010 East MarginalWay South, Seattle, Washington. \n\n\tD.\tA special flight permit may be issued in accordance with FAR 21.197 and 21.199 for the purpose of flying the aircraft which has exceeded the compliance period to a maintenance facility where the modification can be performed. \n\n\tThis amendment becomes effective on March 2, 1984.