The Federal Aviation Administration (FAA) asked operators of certain Boeing 737 NGs to conduct safety inspections after structural cracks were reported by the manufacturer. Boeing notified the agency after cracks were discovered during modifications on a “heavily used aircraft”. Subsequent inspections uncovered similar cracks in a small number of additional planes.

According to KOMO News, the concerned part was the pickle fork of a Boeing 737NG that logged 35,000 flight cycles, about half of the service lifespan for this aircraft. The pickle fork is the part that connects the fuselage with the wings, and manages stress and torque loading that bends the structure during operation. A complete failure of this structural component could have devastating consequences for the aircraft. The pickle forks are designed to last 90,000 life cycles – the whole service life of a Boeing 737NG.

So far, cracks were found on “three Boeing 737-800s having more than 36,000 flight cycles,” an official of the Indian Directorate General of Civil Aviation (DGCA) told the Times of India. Boeing intends to inspect all Boeing NGs (737-600, 737-700, 737-800, and 737-900) above 26,000 flight cycles. It said it would work with its customers to “implement a recommended inspection plan for certain airplanes in the fleet”.

Similarly, an airworthiness directive is expected from the FAA for October 1, 2019, which will give operators instructions to conduct specific inspections, make any necessary repairs and report their findings to the agency. It is unclear for now how many aircraft are concerned by those inspections. In total, over 7,000 Boeing 737 NGs have been ordered worldwide, and more than 6,000 of these aircraft are currently in service.

Boeing made it clear that neither the currently grounded 737 MAX nor the P-8 Poseidon (a maritime patrol aircraft based on the same airframe) were concerned by the potential cracks.

This is yet another problem for Boeing. While currently facing strong criticism regarding its Boeing 737 MAX, its manufacturing practices are also under scrutiny regarding the KC-46 Pegasus and at least one of its Boeing 787 Dreamliner.

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The National Transportation Safety Board (NTSB), the investigative agency responsible for civil transportation accident investigation, criticized the certification of the 737 MAX by Boeing and the Federal Aviation Administration (FAA) for misjudging the reaction of pilots in case of malfunction of the MCAS system that caused the crashes of Lion Air and Ethiopian Airlines. This misinterpretation could have consequences for other aircraft certified in the United States.