Miramar, Florida(CNN) Aviation investigators are looking into two American companies that handled the sensor at the center of the Lion Air crash last year, according to multiple sources familiar with the case.
The sensor, a vane located on the front of the Boeing 737 Max model known as the angle-of-attack (AoA) sensor, fed incorrect data to the flight control system of the Lion Air plane, activating an anti-stall software on the aircraft that repeatedly pitched the plane downward before its crash into the Java Sea, killing 189 people, Indonesian authorities have said.
On Thursday, Ethiopian aviation authorities said that one of the AoA sensors on board the Ethiopian Airlines flight that crashed last month was also producing faulty data, activating the same automatic flight control system that pilots battled before that plane's crash, which killed 157 people.
The Indonesian and Ethiopian investigators have only both released preliminary reports, and they do not specify a cause for the crashes.
The sensor on the Lion Air flight had been repaired by Xtra Aerospace, a company in Miramar, Florida, in 2017, before it was returned to Lion Air and later installed on the doomed flight, according to Nurcahyo Utomo, an investigator with Indonesia's National Transportation Safety Committee.
The part sat in storage with the airline until it was put on the Lion Air plane the day before it crashed, Utomo said.
The US National Transportation Safety Board, which is assisting Indonesian authorities in the Lion Air investigation, is looking into work done on the sensor at the company in the aftermath of the crash at the request of the Indonesian aviation authority, according to Utomo.
In a statement, Xtra said that the part had "conformed to and passed all required and mandated tests" before it was delivered to Lion Air in November 2017, and that the company is cooperating with investigators.
"Our thoughts and condolences are with all those who have lost loved ones in the recent 737 Max 8 accidents," the company said. "Xtra is fully committed to supporting any investigations into this matter."
An airline that receives a refurbished part, like Lion Air, would be responsible for installing it in accordance with the aircraft maintenance manual and performing any required tests on it, according to aviation experts.
The manufacturer of the AoA sensor used on Boeing's 737 Max model, Rosemount Aerospace, was also visited by NTSB investigators after the Lion Air crash, according to a former engineer at the company who requested anonymity because he was not authorized to speak for the company.
A spokeswoman for United Technologies, which owns the Burnsville, Minnesota-based Rosemount, declined to comment.
Bloomberg first reported the involvement of the two companies in the AoA's development and maintenance.
It is routine for crash investigators to visit facilities that handled a part that could have played a role in an accident.
"The whole manufacturing and storage and installation of that component, the Angle of Attack sensor, is under investigation and that's what the NTSB guys are doing down there," said Dr. Alan Diehl, a former NTSB investigator, who is not working on this investigation and was speaking in general about his experience in crash investigations.
"That doesn't mean that there's anything wrong -- that's why they're investigating," Diehl said.
The NTSB declined to comment to CNN.
The former Rosemount engineer expressed astonishment that Boeing had originally designed the anti-stall software, known as the Maneuvering Characteristics Augmentation System, or MCAS, to draw from only one of two AoA sensors on the nose of the plane.
"How that got certified is something that's a mystery to us," he said.
The Justice Department is currently probing Boeing and the Federal Aviation Administration's certification and marketing of the plane, CNN has reported.
Boeing last week announced that they were updating MCAS to draw data from the two AoA sensors, adding a level of redundancy to the system.
Elements of plane design are classified by regulators for their risk of failure, which determines the level of redundancy needed. The higher the risk of failure, the more redundancy required.
Boeing officials have said that the software in its initial design had been classified at a level of risk of failure that, in line with industry standards, didn't require data from a second sensor.