FAA Identifies New Issue With 737 MAX

An un-grounding date for Boeing's 737 MAX is not yet on the horizon.

As Boeing works with airlines, regulators and other stakeholders to fix a flight control system suspected of contributing to two fatal crashes of the airliner, the Federal Aviation Administration found a previously-unknown flaw that it will require Boeing to fix.

According to a source familiar with the situation, the software update proposed by Boeing was undergoing simulator testing last week. During the test, the source said, FAA pilots discovered an issue that affected their ability to recover from a runaway stabilizer trim. The issue was eventually traced to how the flight computers were processing data.

Runaway stabilizer trim is a signal of activation of the Maneuvering Characteristics Augmentation System, or MCAS, the flight-control code suspected of being at the root of the two accidents, which killed 346 people.

“The safety of our airplanes is Boeing’s highest priority," a Boeing spokesman said in an email, confirming that the FAA had identified the issue during a simulator session."Boeing agrees with the FAA's decision and request, and is working on the required software," the company's statement added. "Addressing this condition will reduce pilot workload by accounting for a potential source of uncommanded stabilizer motion," Boeing said. Stabilizers are the part of a plane's tail that controls pitch, i.e. points the nose up or down.

The FAA said it will not announce a date to lift the MAX grounding order until all issues with the plane are addressed.

"The FAA is following a thorough process, not a prescribed timeline, for returning the Boeing 737 Max to passenger service. The FAA will lift the aircraft’s prohibition order when we deem it is safe to do so," the agency said in a statement. "We continue to evaluate Boeing’s software modification to the MCAS and we are still developing necessary training requirements."

Meanwhile, airlines continue to push back their planned reintroduction of the MAX into service. United Airlines announced Wednesday that the plane would be off its schedule until at least Sept. 3. American Airlines made a similar announcement earlier this month, but last week, American's CEO seemed to suggest the plane may be out of service beyond that date. The groundings have resulted in thousands of canceled flights every month as airlines struggle to cope with the resulting shortage of aircraft.