Summary
The FAA proposes to supersede an existing airworthiness directive (AD) that applies to certain Boeing Model 747 series airplanes. The existing AD currently requires repetitive inspections for cracking and corrosion of all exposed surfaces of the carriage spindles (including the inner bore and aft links) of the trailing edge flaps, and additional inspection and corrective action if necessary. The existing AD also requires repetitive overhaul of the carriage spindle and aft link, which terminates the repetitive inspections. This proposed AD would add a repetitive inspection to detect broken parts, and revise the overhaul threshold and repetitive intervals. This proposed AD results from analysis that showed additional inspections should be done to prevent the loss of a flap, and that the flight-hour- based interval should be revised to a flight-cycle-based interval, because the greatest loads on the spindles happen during takeoff and landing. We are proposing this AD to detect and correct failed carriage spindles or aft links for the inboard or outboard trailing edge flaps. Such failure could cause the flap to depart the airplane, reducing the flightcrew's ability to maintain the safe flight and landing of the airplane.