76-17-07 BOEING: Amendment 39-2706. Applies to Boeing Model 727-100 series airplanes certificated in all categories with static port heater circuits deactivated. Compliance required as indicated unless already accomplished. \n\tTo prevent the loss of altitude and airspeed reference due to a small amount of water freezing in the static port system, accomplish either of (1) or (2) below: \n\t(1)\tWithin the next 1,000 hours time in service after the effective date of this AD reactivate the static port heater circuits to the original FAA approved Boeing 727-100 configuration; or \n\t(2)\tWithin the next 2,000 hours time in service after the effective date of this AD replace the deactivated heater assembly, P/N 10-60723-1, with elbow fitting MS21908D6 in accordance with Boeing Service Bulletin 727-34-95 dated September 3, 1976, or later FAA approved service bulletins, and enlarge the static port sensing holes from .047 inch diameter to .125 inch diameter in accordance with Boeing ServiceBulletin 727-34-94 (to be released) or later FAA approved service bulletins. \n\tNotwithstanding the provisions of the above paragraph (1) the heater elements in one static system may be inoperative provided the aircraft is not flown in icing or precipitation conditions. \n\tBoeing 727-100 airplanes already incorporating Boeing Service Bulletin 727-25-42, Revision 1, dated March 4, 1968, with elbow fitting MS21908D6 and Boeing Service Bulletin 727-34-57 dated April 7, 1968, enlarging the static sense holes are in compliance with this AD. \n\tEquivalent modifications may be approved by the Chief, Engineering and Manufacturing Branch, FAA Northwest Region. \n\tThe manufacturer's specifications and procedures identified and described in this directive are incorporated herein and made a part hereof pursuant to 5 U.S.C. 552(a)(1). \n\tAll persons affected by this directive, who have not already received these documents from the manufacturer, may obtain copies upon request to Boeing Commercial Airplane Company, P. O. Box 3707, Seattle, Washington 98124. The documents may also be examined at FAA Northwest Region, 9010 East Marginal Way South, Seattle, Washington.\n \n\tThis amendment becomes effective October 1, 1976.