AD 70-04-03

70-04-03 BOEING: Amdt. 39-941 as amended by Amendment 39-1020. Applies to Model 737 series airplanes.

Compliance required as indicated unless already accomplished.

To prevent possible damage to airplane structure, systems and components due to failure of the APU bleed air duct or failure of the APU fire extinguisher bottle to discharge safely, or from exposure to an overheat condition following ground operation of the pneumatic system with bleed air from the APU or external ground service, accomplish the following:

(a) Within 25 hours time in service after the effective date of this directive,

(1) Install a placard in full view of the pilot to read: "Discharge APU fire extinguisher bottle whenever left bleed air overheat light illuminates", or "Discharge APU fire extinguisher bottle whenever left bleed air wing-body overheat light illuminates."

(2) Install a placard in the cockpit in full view of the pilot and install an external placard adjacent to thepneumatic ground service connection to read: "Monitor cockpit bleed air overheat system during all operations of the pneumatic system", or "Monitor cockpit bleed air wing-body overheat system during all operations of the pneumatic system."

(b) In lieu of the placard installations required by para. (a)(2), the cockpit bleed air wing- body overheat system and master caution light must be checked prior to further flight for an overheat condition following ground operation of the pneumatic system with bleed air from the APU or external pneumatic ground service. If an overheat condition exists, the source of the overheat condition must be established. Inspect the airplane structure, systems and components for overheat damage and repair if necessary.

(c) Within 50 hours time in service after the effective date of this AD, unless already accomplished within the last 500 hours time in service prior to the effective date of this AD, and thereafter at intervals not to exceed 500 hours time in service, inspect the APU bleed air duct, part number 69/37931-3, -4, or -6 for cracks and replace cracked ducts in accordance with Boeing Alert Service Bulletin 36/1003 dated 17 January 1970 or later FAA approved revision, or method approved by the Chief, Aircraft Engineering Division, FAA Western Region.

(d) In lieu of the placards and procedures required in paragraphs (a) and (b), remove APU fire extinguisher container, Part Number 806000-21 and install Part Number 806000-31 container in accordance with Boeing Service Bulletin 26-1011, dated June 9, 1970, or later FAA approved revision or an equivalent method approved by the Chief, Aircraft Engineering Division, FAA Western Region.

NOTE: Do not insert operational procedure specified in revision 1, dated 19 January 1970, to step E of Boeing S.B. 36/1003."

Amendment 39-941 effective upon publication in the Federal Register for all persons except those to whom it was made effective immediately by telegram dated 31 January 1970.

This Amendment (39-1020) becomes effective July 9, 1970.