64-01-02\tBOEING: Amdt. 668 Part 507 Federal Register January 7, 1964. Applies to All Models 707 and 720 Series Airplanes Listed in Boeing Service Bulletin No. 1788. \n\n\tCompliance required within 6,000 hours' time in service after the effective date of this AD unless already accomplished. \n\n\tInstances of engine burner case burn through have occurred in service resulting in damage to the nacelle and lower strut in which detection of the fire was delayed because there are no fire detector elements in the area on top of the engine. To correct this unsafe condition, the following must be accomplished:\n \n\tInstall additional fire detector elements (continuous or unit type) between the horizontal firewall and the top of the engine in the area between nacelle Stations 160 and 180. This additional detector installation shall be made in accordance with Boeing Service Bulletin No. 1788 dated July 11, 1963, or in accordance with an installation approved by the Chief, Engineering and Manufacturing Branch, FAA Western Region. \n\n\t(Boeing Service Bulletin No. 1788 covers the installation applicable to the various fire detector systems as installed on different groups of airplanes.) \n\n\tThis directive effective February 7, 1964.