Summary
The FAA proposes to supersede an existing airworthiness directive (AD) that applies to all Model 737-100, -200, -200C, -300, - 400, and -500 series airplanes. The existing AD currently requires repetitive inspections to find cracks, fractures, or corrosion of each carriage spindle of the left and right outboard mid-flaps, and corrective action if necessary. The existing AD also currently requires repetitive gap checks of the inboard and outboard carriage of the outboard mid-flaps to detect fractured carriage spindles, and corrective actions if necessary. This proposed AD would require any new or serviceable carriage spindle installed per the requirements of the existing AD to meet minimum allowable diameter measurements taken at three locations. This proposed AD also would require new repetitive inspections, measurements, and overhaul of the carriage spindles, and applicable corrective actions. In addition, this proposed AD would require replacing any carriage spindle when ithas reached its maximum life limit. This proposed AD results from reports of fractures that resulted from stress corrosion and pitting along the length of the spindle and spindle diameter, and additional reports of corrosion on the outboard flap carriage spindles. We are proposing this AD to detect and correct cracked, corroded, or fractured carriage spindles, and to prevent severe flap asymmetry, which could result in reduced control or loss of controllability of the airplane.