US regulators are ordering operators of winglet-equipped Boeing 767-300s to conduct checks on the wing structure following occurrences of fatigue cracking.
Aviation Partners Boeing formally launched its winglet for the 767-300ER in 2007 and, two years later, American Airlines put the modification into service.
The winglets have since been adopted by several carriers including US operators Delta Air Lines, United Airlines and UPS.
In an airworthiness directive the US FAA states that operators need to conduct high-frequency eddy-current inspections for cracking of the lower outboard wing skin on the modified aircraft.
It also orders follow-up actions including repeat inspections, modification of internal stringers, and other measures.
The FAA says the fatigue cracking in the wing skin could potentially result in separation of the winglet and reduced controllability.
It says the directive affects some 140 US-registered aircraft.
Certain aircraft, identified in a service bulletin issued by Aviation Partners Boeing last year, are unaffected owing to a change incorporated into winglet retrofit kits.
European operators of winglet-equipped 767s include Austrian Airlines, Condor and Icelandair.