This is a lengthy read, but worth it. I'll quote the main piece I am speaking of.

At the Bali airport, a vane, known as an angle of attack sensor, was replaced. Crash investigators were presented with photographs supposedly showing that a mandatory test was done after the vane had been replaced. But upon further inspection, investigators concluded the photos were from a different aircraft. “This is a test that Lion Air was required to do, and they didn’t,” said John Cox, an aviation safety consultant. If the test had been done, engineers likely would have realized the vane was calibrated incorrectly by 21 degrees

Source: nytimes.com

On Friday, October 25th, 2019, the FAA revoked the repair station certificate of the Florida repair shop that had sold the second-hand part to Lion Air.

The FAA revocation order said Xtra “recklessly and systemically” failed to comply with federal safety requirements.

Source: Seattle Times

Would the finding in the first article imply the Florida repair shop can reopen for business? Or, did they sell Lion Air the AoA and was miscalibrated by them, and therefore the business will remain closed?

AoA = angle-of-attack


2 Answers 2


The FAA action, while supposedly not directly related Lion Air but more to Xtra's problems with working on parts they were not authorized to work on because they hadn't demonstrated that had everything in place, is obviously politically related to the event because the crash put the spotlight on Xtra and the FAA had to do something once having lifted that particular rock.

So from a strictly legal standpoint, Lion Air's maintenance actions don't help Xtra and what will happen is Xtra will have to make reforms and then go back to the FAA to try to get their repair cert reinstated independently of any Lion Air actions.

Normally what happens is a part goes to a repair facility, and the repair shop puts it though an Acceptance Test Procedure (ATP) as per the manufacturer's Component Maintenance Manual (CMM). There is usually some kind of test rig that has to be made (instructions for making it in the CMM), that runs the specified functional tests on both ingoing and outgoing parts.

So the part goes in, and gets an incoming ATP. If it passes the incoming ATP, it's considered serviceable and gets tagged NFF (No Fault Found) and sent back to the airline as serviceable. If it fails ATP, it gets broken down and repaired as required. It then gets an outgoing ATP (the same test normally) to validate function before it is tagged repaired/serviceable.

I can't really tell from the article if the mis-calibration was inherent to the vane as received or was something screwed up when the airline installed it. Notwithstanding the likelihood that Xtra was turning parts around that they don't appear to be approved to repair, it's not uncommon for parts to come back to an airline NFF, or repaired, and still fail when it's installed on the plane.

So either Xtra had the proper manual, test rig, parts and tools, training etc. for fixing these vanes or they didn't. The FAA's action makes it sound like they didn't and were maybe just receiving units and doing some other test they made up themselves, or maybe just smiled at it and sent it back out. Hard to say.

In any case, receiving a part back with a serviceable tag is no ironclad guarantee that it will work in service, and "bad from spares stock" happens from time to time. No system is perfect. The business depends to some degree on the redundancy of having two and three of everything to cater to random failures no matter the background causes, except in this instance Boeing decided to let that single-point-of-failure spot in the system architecture get through cert, and here we are.


As part of the investigation the authorities followed that part through the system and scrutinized every step of the AoA's life. When they looked at Xtra they found numerous issues with the company and how they handled repairs. The FAA's press release on Xtra says:

According to the order, 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. The company also failed to comply with procedures in its repair station manual for implementing a capability list in accordance with the Federal Aviation Regulations. Xtra is a repair station certificated under part 145 of the Federal Aviation Regulations.

Translation: they didn't stick to what they were allowed to fix, they weren't supposed to try to fix the AoA sensor. Next:

The FAA began its investigation in November 2018. Investigators looked specifically at the company’s compliance with regulatory requirements that apply to its capability list, and records and work orders for aircraft parts it approved for return to service. The investigation determined that 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. 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.

Translation: For a decade Xtra can't say for sure what they fixed or how they fixed it, and couldn't show they had the tools or the talent to fix anything they were allowed to.

So Xtra have a serious systemic problem, almost every single part they have ever touched is now suspect, so they've been shut down. I don't know whether the repair to the AoA was faked or simply botched with bad records, but either way I wouldn't want to fly in an airplane which had safety critical parts from Xtra.


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