The US Federal Aviation Administration has finalised a rule requiring new inspections to prevent fuselage cracks opening on Boeing 737 Classics.
The airworthiness directive will cost operators between $48,100 to $65,900 per aircraft, depending on the amount of repair work required after inspections are completed.
The directive directly impacts a total of 109 737-300s/-400s/-500s in service by US operators.
The most expensive job required by the rule are a series of new non-destructive inspections, including checks using a medium frequency eddy current, magneto optical imaging, C-scan or ultrasonic phased arrays.
The intervals between inspection range greatly depending on the aircraft configuration, but span anywhere between 500 flight cycles and 2,400 flight cycles.
The FAA issued the new directive less than two years after a fuselage lap-joint failed on a Southwest 737-300 on 1 April 2011, forcing the aircraft to land in Yuma, Arizona.
That incident prompted emergency inspections across the 737 Classic fleet of fuselage lap-joints, but those revealed the need to expand similar checks in more areas of the fuselage.
Specific areas now under study include the horizontal chem-mill near the lap-joints over the entire area of the fuselage crown and vertical chem-mill cracks next to butt joints.