The FAA issued a new airworthiness directive (AD) for next-generation Boeing 737 aircraft that could cost U.S.-based operators up to $10.1 million. The AD applies to 737-600, -700, -700C, -800, -900 and -900ER aircraft after the agency found that protective coatings for wear and corrosion were incorrectly applied to the aircraft family’s horizontal stabilizer rear spar. Premature failure of the attach pins could cause reduced structural integrity of the horizontal stabilizer to fuselage attachment, resulting in a loss of control of the aircraft, according to the directive. The inspection and replacement of the attach pins is estimated to cost $9,267 per aircraft, or a total of $10.1 million for the 1,050 airplanes in the U.S. registry that are affected by the AD. FAA issued a notice of proposed rulemaking regarding the AD in September 2012, and the directive becomes effective May 20. Boeing told FAA that some of the costs associated with the repairs could be covered under warranty.