The US Federal Aviation Administration has revoked the aircraft repair station licence held by Xtra Aerospace, the Florida shop that repaired the angle-of-attack (AOA) indicator investigators say contributed to the 2018 crash of a Lion Air Boeing 737 Max.
The FAA ordered that the shop's licence be pulled on 25 October, the same day Indonesia's National Transportation Safety Committee issued a report concluding that Xtra likely calibrated the AOA sensor incorrectly.
"Xtra failed to comply with requirements to repair only aircraft parts on its list of parts acceptable to the FAA that it was capable of repairing," says the FAA. "The company also failed to comply with procedures in its repair station manual for implementing a capability list in accordance with… regulations."
Xtra's public relations firm issued a statement saying the company disputes the FAA's findings.
“We have been cooperating closely with the FAA throughout its investigation and though we have reached a settlement with the FAA, we respectfully disagree with the agency’s findings," says Xtra's statement.
"The FAA’s enforcement action is separate from the [NTSC's] investigation and report of the Lion Air Boeing 737 Max accident and is not an indication that Xtra was responsible for the accident," Xtra adds. "Safety is central to all we do, and we will continue cooperating with the authorities. We would like to express our deep sadness and sympathy for all those who have lost loved ones in the Lion Air Flight 610 accident.”
The NTSC says the AOA sensor was misaligned by about 21 degrees, an error which led the aircraft's maneuvering characteristics augmentation system (MCAS) to activate, pushing the aircraft nose down. The pilots were unable to recover.
"This immediate 21-degree delta indicated that the AOA sensor was most likely improperly calibrated at Xtra Aerospace," says the NTSC's report.
The sensor on the Lion Air 737 Max had previously been installed on the right side of a 737-900ER operated by Malaysia's Malindo Air. It was removed from that aircraft in August 2017 following "maintenance write-ups" related to speed and altitude warnings appearing on the co-pilot's display, says the report.
Having been sent to Xtra for repair in October 2017, the sensor failed an operational test. "The preliminary result stated that the eroded vane caused erroneous readings," says the NTSC.
Repair records show that Xtra replaced the eroded vane, and calibrated and tested the sensor. "The work order stated that the results for the required tests were satisfactory," says the report.
Xtra sent the AOA sensor back to Malindo in November 2017, and in October 2018 it was sent to Denpasar, Indonesia, where technicians installed it on the crashed Lion Air 737 Max 8. The NTSC could not determine if an AOA test was completed properly when the part was installed.
The FAA says it started investigating Xtra in November 2018, looking "specifically at the company's compliance with regulatory requirements… and records and work orders for aircraft parts it approved for return to service".
"From November 2009 until May 2019, Xtra failed to complete and retain records in accordance with procedures in its repair-station manual to support parts on its capability list," says the FAA. "The company also did not substantiate that it had adequate facilities, tools, test equipment, technical publications and trained and qualified employees to repair parts on its capability list."
The FAA says the order revoking Xtra's certificate is part of a settlement agreement under which the company waives its right to appeal the decision.
Story updated on 25 October to include Xtra's statement.