Few airplanes have generated as much discussion, controversy and media attention as the Boeing 737 Max.

Designed as the fourth and most efficient version of the narrow-body Boeing 737 (BA) - Get Free Report, the new type of aircraft had its maiden flight in January 2016 but was then grounded worldwide between March 2019 and November 2020 after two crashes that took the lives of 346 people.

Later investigations determined that the crashes occurred due to a failure in the planes' maneuvering characteristics augmentation system (MCAS) used to stabilize planes in flight. In 2021, Boeing paid $2.5 billion to settle Department of Justice allegations that it defrauded the Federal Aviation Administration (FAA) by covering up defects.

Another Max 737 Problem Halts Plane Deliveries
After requiring Boeing to institute new MCAS training and certain design changes, the FAA eventually cleared Boeing 737 Max's return to the skies by the end of 2020 — in October 2022, Alaska Airlines (ALK) - Get Free Report committed to buying 52 Boeing 737 Max planes for delivery between 2024 and 2027. It's also currently in the process phasing out its other aircraft in the hope of becoming a single-carrier airline by the end of 2023.

The plane is Boeing's most popular design. The company delivered 111 of the planes in the first quarter and has been targeting increasing production to 38 per month by June, Reuters reported.

However, as numerous other airlines also stock up on the 737 Max, Boeing is now being forced to halt deliveries. On April 13, the company said that it was immediately stopping deliveries of the 737 Max, 737 Max 8 and MAX 8-200 aircraft after being informed of a "non-standard manufacturing process" from a supplier.

Spirit AeroSystems (SPR) - Get Free Report made the two fittings in aft fuselages used in the rear of the planes.

Boeing told CNN that a "significant number" of planes were affected. While the defect is not “an immediate safety of flight issue," according to the plane maker, it needs to be looked into amid higher risk due to manufacturing inconsistencies.

Boeing Working With FAA on Issue
Boeing also said that it has notified the FAA of the situation and is now working with the agency to inspect and fix any potential problems.

This will, however, cause "lower near-term 737 MAX deliveries while this required work is completed."

In a statement, Boeing said "We regret the impact that this issue will have on affected customers and are in contact with them concerning their delivery schedule." It added. "We will provide additional information in the days and weeks ahead as we better understand the delivery impacts."

United (UAL) - Get Free Report, which has a large fleet of Boeing 737 Max planes and was one of the airlines that recently purchased new ones, said that it does not expect the halted deliveries to have "any significant impact on our capacity plans for this summer or the rest of the year."

Boeing shares fell in after-hours trading after news of the delivery halt broke and, as of Friday afternoon, were still down more than 6% at $200.76. Spirit AeroSystems stock, meanwhile, plunged by more than 20%.

As demand for air travel continues to rise, many airlines are finally looking to expand their fleet after many canceled Boeing orders during the pandemic.

Since the 2019 grounding of the Max 737, Boeing has reported only two profitable quarters — the last one in the summer of 2022.