Airworthiness Directives; McDonnell Douglas Corporation Model DC-9-14, DC-9-15, and DC-9-15F Airplanes; and Model DC-9-20, DC-9-30, DC-9-40, and DC-9-50 Series Airplanes

We are superseding an existing airworthiness directive (AD) for the products listed above. That 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 new 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 new AD also adds certain airplanes to the applicability. This AD was prompted by 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 of the rear spar upper cap, which resulted from stress corrosion. We are issuing 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.