Refined satellite tracking data combined with some non-defined physical evidence from the wreckage of the Ethiopian Airlines crash site prompted Canada, then the US to ground the Boeing 737 MAX.

The morning of March 13, Canada’s transport ministry announced that country’s grounding. Three Canadian airlines—Air Canada, WestJet and Sunwing—have MAXs in their fleets.

Hours later the same day, the US abruptly changed course when President Donald Trump announced the US was also grounding the MAX—the last country to do so. American Airlines, Southwest Airlines and United Airlines operate MAXs.

Previously, FAA and US Department of Transportation (DOT) had said there was no evidence linking the March 10 Ethiopian flight 302 MAX 8 crash to the Lion Air MAX 8 crash, flight 610, that occurred in Indonesia in October. They stood by a decision to not ground the MAX; Boeing and the US airlines supported the decision, saying they were confident in the MAX’s safety.

Given that the two black box recorders retrieved from the Ethiopian wreckage were still unopened and unexamined Wednesday, the new evidence had to be something else.

FAA’s emergency order stated the new information concerned “the aircraft's configuration just after takeoff that, taken together with newly refined data from satellite-based tracking of the aircraft's flight path,” indicated similarities with what happened with the Lion Air flight.

"Suffice it to say the evidence found on the ground made it more likely that the flight path was closer to Lion Air," FAA acting administrator Dan Elwell told reporters after the order was released.

The order's language suggests discovery of wreckage that establishes the aircraft's flight-control surface positions. Flight 610 began to experience flight-control issues shortly after retracting its flaps after takeoff. Those issues are the focus of that ongoing investigation.

The refined satellite data, meanwhile came from space-based ADS-B provider Aireon.

"The way the [initial] data was presented, it was not showing credible movement of an aircraft," Elwell said.

The resulting track, including flight 302's altitude variations, lined up closely with 610’s known track. This suggests 302 was struggling to maintain altitude and then dove rapidly to impact, as happened with 610 and which is why the Indonesian crash investigation is focused on the MAX’s maneuvering characteristics augmentation system anti-stall software. That investigation, like 302, is ongoing.

Canadian transport minister Marc Garneau said that while links between the two crashes were still not conclusive, “there are similarities that exceed a certain threshold in our minds."

FAA’s Elwell, explaining why the agency was the last to issue a MAX grounding, said, "we are a fact-driven, data-based organization. We make actions based on data, findings and risk assessment. That data coalesced today and we made the call."

But questions will be asked about the gap between Canada’s and the US’ grounding decisions. Did the regulatory authorities of each country have access to that satellite data and wreckage information at about the same time? If so, what led the US authorities to wait more than three hours after Canada? And why did the US president make that announcement, not FAA or DOT?

US lawmakers were quick to raise those questions and call for oversight of FAA’s decision-making processes.

US House Transportation and Infrastructure Committee chair Peter DeFazio (Dem-Oregon), and House aviation subcommittee Chair Rick Larsen (Dem-Washington) issued a statement late Wednesday afternoon saying, “Despite repeated assurances from the FAA in recent days, it has become abundantly clear to us that not only should the 737 MAX be grounded but also that there must be a rigorous investigation into why the aircraft, which has critical safety systems that did not exist on prior models, was certified without requiring additional pilot training. While a lot of data has yet to be recovered that will help explain why Ethiopian Airlines flight 302 went down, as chairs of the committee and subcommittee with jurisdiction over the FAA and NTSB, we plan to conduct rigorous oversight with every tool at our disposal to get to the bottom of the FAA’s decision-making process.”

Karen Walker karen.walker@informa.com