In April 2023, a manufacturing fault was discovered inside parts of the Boeing 737 MAX, one of the world’s most popular passenger jets. The problem, found inside the structure that connects the aircraft’s tail fin to its body, had gone undetected for up to four years. Boeing confirmed that the fault did not put in-service planes at risk, but repairing it would delay the delivery of more than 170 aircraft to airlines around the world.
How the Problem Was Found
On 12 April 2023, Spirit AeroSystems — the company that builds the fuselages for Boeing’s 737 family at its factory in Wichita, Kansas — notified Boeing that workers had used a non-standard manufacturing process when attaching the vertical tail to the back of certain aircraft. Spirit AeroSystems is one of Boeing’s most important suppliers, responsible for producing the main body sections of the jet. The vertical tail is the upright fin at the rear of the plane that helps it fly in a straight line; it connects to the fuselage at eight points. Engineers found that two of these connection points did not meet the requirements set by the Federal Aviation Administration (FAA), the US aviation regulator.
Workers had drilled some of the required holes in the wrong position or added duplicate holes by mistake. The error may have been present since 2019, when the 737 MAX returned to production after a lengthy global grounding that followed two fatal crashes and killed 346 people. This meant the problem had gone undetected for about four years. The defect affected the 737 MAX 7 and the 737 MAX 8, but not the larger MAX 9.
After reviewing the situation with the FAA, Boeing confirmed that aircraft already flying with passengers were safe to continue in service, because the fault did not affect the immediate structural integrity of the plane. However, all undelivered aircraft had to be inspected and repaired before they could be handed over to airlines.
What Happened Next
Fixing the problem was not simple. Because the fittings were located deep inside the aircraft’s structure, workers at Spirit AeroSystems’ factory had to partially disassemble each plane to reach the affected area and install correctly positioned fittings. Boeing identified more than 170 aircraft that needed this rework before they could be delivered.
The repairs had a significant impact on Boeing’s delivery targets for 2023. The company had planned to hand over between 400 and 450 aircraft from the 737 family during the year, but delivered only 396 by December. Airlines waiting for new jets — including Southwest Airlines, one of the 737 MAX’s biggest customers — had to adjust their schedules as a result.
Spirit AeroSystems accepted responsibility for the error and recorded 23 million dollars in costs related to the repairs. The rework was completed by July 2023. The incident reinforced growing concerns about manufacturing quality at Boeing and its supply chain, raising fresh questions about the inspection procedures used at one of the world’s largest aircraft manufacturers.
Key vocabulary:
- fuselage – the main body of an aircraft, which carries the passengers, crew and cargo
- vertical tail – the upright fin at the rear of an aircraft that helps it fly in a straight line; also called the vertical stabiliser
- non-standard manufacturing process – a way of building something that does not follow the approved method; in aviation, every production step must follow strict rules set by regulators
- rework – repairs carried out on a product that was already built but does not meet the required standard; in aviation, rework typically means returning to an earlier stage of production
- delivery – when an aircraft manufacturer officially hands a completed aircraft to an airline; the airline takes legal ownership of the aircraft at this point
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