Airline passenger organisation Flyers Rights has challenged the US Federal Aviation Administration’s (FAA) decision to return the grounded Boeing 737 MAX aircraft to service.

A notice of appeal has been filed in the DC Circuit Court of Appeals. It follows the agency’s ungrounding order issued on 18 November.

Boeing 737 MAX has been temporarily grounded since March 2019 after two fatal crashes in Indonesia and Ethiopia claimed 346 lives. president Paul Hudson said: “Boeing and FAA first declared the MAX safe in 2017, then again, a second time after the first crash in October 2018, and then incredibly, a third time after the second crash in March 2019.

“Now the FAA and Boeing have declared it safe a fourth time, based on secret data and secret testing that is clearly legally inadequate.”

The US airline passenger advocacy group has petitioned the court to review the final Airworthiness Directive and notification of rescission of Emergency Order of Prohibition.

Hudson, along with Democratic lawmakers, has urged the FAA to disclose more fundamental data in its review.

Hudson added: “After reneging on their multiple 2019 transparency pledges to Congress under oath, to the public, and to shareholders, the FAA and Boeing now insist that the public should trust them this time, all based on secret data and secret testing by anonymous employees.

“Meanwhile, dozens of questions and concerns raised by independent aviation experts have gone unanswered. Pilot retraining has been roundly criticised as inadequate.”

Various aviation organisations, including UAE civil aviation regulator General Civil Aviation Authority (GCAA) and European Union Aviation Safety Agency (EASA), have also started preparations to return the grounded aircraft.