After the Federal Aviation Administration (FAA) issued an Airworthiness Directive (AD) on October 3, 2019, operators of Boeing 737NG aircraft, models 737-600, -700, -700C, -800, -900, and -900ER, were forced to check for cracks on left and right-hand side suspension system, which connects the fuselage with the wings. The system, nicknamed the pickle fork, was designed to safely handle 90,000 flight cycles – the total lifespan of a Boeing 737 NG.

However, cracks were found on two 737NG fuselages that “accumulated between 35,578 and 37,329” cycles, according to the FAA’s issued AD. The U.S. based civil aviation authority estimated that 1,911 Boeing 737NG aircraft are affected in the United States alone. Reportedly, 36 out of 686 checked 737NG aircraft were found to have structural cracks in their outboard chords of frame fittings and failsafe straps, located just above the wheel wells. Boeing expects that each aircraft will have to spend between two to three weeks on the ground in order to repair the pickle fork cracks.

Brazilian airline GOL Linhas Aéreas grounded 11 NGs, while Southwest found two aircraft with structural cracks. The latter carrier is one of the most affected operators in the United States. Out of the 165 aircraft mandating inspection within seven days after the FAA issued the AD in the U.S., almost all of them are operated by Southwest, Reuters reports.

The Airworthiness Directive indicates that any Boeing 737 NG aircraft that have accumulated over 30,000 take-off and landing procedures have to be inspected within seven days of the effective AD date, which is October 3, 2019. Checks are also to be made for aircraft that have not yet accumulated “22,600 flight cycles, or within 1,000 flight cycles after the effective date of this AD, whichever occurs later”, reads the Airworthiness Directive.

The grounded 737 MAX and the P-8 Poseidon, which was developed using the 737 NG airframe, are unaffected by the issues, according to Boeing.