Summary
The FAA proposes to supersede an existing airworthiness directive (AD) that applies to certain Model DC-9-14 and DC-9-15 airplanes; and Model DC-9-20, DC-9-30, DC-9-40, and DC-9-50 series airplanes. The existing AD currently requires repetitive high frequency eddy current inspections to detect cracking in the vertical radius (also known as the "vertical leg'') of the upper cap of the center wing rear spar, and repair if necessary. This proposed AD expands the area to be inspected by including inspections to detect cracking of the horizontal flange of the upper cap of the left and right center wing rear spar, and repair if necessary. This proposed AD also adds certain airplanes to the applicability. This proposed AD results from reports of cracking in the vertical radius of the upper cap of the center wing rear spar, and the horizontal flange on the inboard side of the rear spar upper cap, which resulted from stress corrosion. We are proposing this AD to detect and correct cracking in the vertical leg or the horizontal flange of the upper cap of the left or right center wing rear spar, which could cause a possible fuel leak, damage to the wing skin, and structural failure of the upper cap, and result in reduced structural integrity of the airplane.