The chair of the National Transportation Safety Board (NTSB) wrote a letter to the head of the Federal Aviation Administration (FAA) on Tuesday, expressing concerns that the FAA is not adequately addressing important safety recommendations regarding a recently identified flaw in a Boeing 737 component.

The NTSB made an urgent safety recommendation last Friday, alerting that a specific rudder control component in certain Boeing 737 models may fail under specific cold weather conditions.

Following this announcement, the FAA stated that it had resolved the issue and claimed that no affected parts were being used by U.S. airlines.

However, the letter from the NTSB chair pointed out that the FAA is not doing enough to tackle the issue and noted that it was misleading to claim the parts are not currently in operation by U.S. carriers.

“I am worried that the FAA has not given this issue the attention it requires until we made our urgent safety recommendation public,” NTSB chair Jennifer Homendy stated in her letter. “It disappoints me that there do not seem to be immediate plans from the FAA to address the risks linked to jammed rudder controls in the six months since we published our preliminary report on this matter.”

The NTSB’s investigation was triggered by a control loss incident involving a United Airlines flight back in February. The letter also mentioned two comparable events from 2019 related to foreign airlines. It clarified that the FAA’s assertion about the parts being out of service with U.S. airlines is incorrect.

The NTSB’s findings suggest that, according to information obtained from Boeing and the component manufacturer, there may still be around 16 affected parts in use on U.S. aircraft, with hundreds more potentially installed or held as spare parts worldwide.

The letter also criticized Boeing for failing to properly notify other airlines about the potentially defective components.

In reaction to the NTSB’s letter, the FAA released a statement indicating it takes all NTSB recommendations seriously.

“The FAA is working swiftly to set up a discussion with the relevant civil aviation authorities to ensure they have the necessary information from the FAA, including any recommended actions,” the statement noted. “The FAA will also be issuing a Continued Airworthiness Notification to the International Community (CANIC) and plans to conduct further simulator testing in October.”