South Korean authorities confirmed that inspections for Boeing 737NG pickle fork cracks have been completed in the country. Out of a total 150 aircraft checks completed, double cracks were detected on 13 aeroplanes, Ministry of Land, Infrastructure and Transport (MOLIT) revealed on November 25, 2019. 

The majority of inspections, 100, were carried out by November 10, 2019, with further 50 between November 10-25, 2019. Pickle fork cracks were detected only during the first round of check-ups, according to MOLIT, which stated no cracks were detected on the aircraft checked after November 10. 

Double cracks were detected on 13 aircraft, which were immediately grounded. Two of the aircraft, one belonging to Jin Air and one to Korean Air, have already been repaired and returned to service. 

Eleven planes remain grounded until repairs are done ‒ something that the ministry hopes will be achieved by January 2020. After that, the planes’ safety will have to be confirmed by aviation safety inspector before they can return to service. 

Meanwhile, the aircraft on which no damage was detected, will be inspected repeatedly within 3,500 flights, according to the ministry, which argues that the action is needed for safety.  

Following a second round of inspections, pickle fork cracks were found on four Boeing 737 NG, bringing the total number of grounded aircraft in South Korea to 13. 

Information about the 13 aircraft affected by fuselage cracks were sent to Boeing. The maintenance works means replacing the affected parts and lasts approximately two weeks per aircraft. All 13 affected aircraft are expected to be repaired by January 2020, the ministry states. 

The pickle fork is a suspension system that connects the fuselage with wings and manages stress and torque loading that bends the structure during operation. It is designed to withstand 90,000 life cycles – the whole service life of a Boeing 737NG.

The problem in question was identified in late September 2019, after cracks were found on the pickle fork during the passenger-to-freighter conversion of a Boeing 737-800 NG that logged 35,000 flight cycles, about half of the service lifespan for this aircraft. Preliminary inspections found similar issues on at least 36 other Boeing 737-800s having more than 36,000 flight cycles.

After a recently issued FAA Airworthiness Directive, the first 737 NG aircraft are grounded after the initial inspection:

On October 3, 2019, the Federal Aviation Administration (FAA) issued an Airworthiness Directive (AD), which required Boeing 737NG (models 737-600, -700, -700C, -800, -900, and -900ER) operators to have their aircraft checked for cracks on the suspension system. 

In total, over 7,000 Boeing 737 NGs have been ordered worldwide, and more than 6,000 of these aircraft are currently in service.