Airworthiness Directives; Boeing Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-200C, 747-200F, 747-300, 747-400, 747-400D, 747-400F, and 747SR Series Airplanes

The FAA is superseding an existing airworthiness directive (AD) that applies to certain Boeing Model 747 series airplanes. That 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. That AD also currently requires repetitive overhaul of the carriage spindle and aft link, which terminates the repetitive inspections. This new AD adds a repetitive inspection to detect broken parts, and revises the overhaul threshold and repetitive intervals. This 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 issuing this AD to detect and correct failed carriage spindles or aft links of 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.