"We don't is the short answer," CNN aviation correspondent Richard Quest
Those decisions are alarming.
"You have to remember most pilots would never go to these extremes," Quest said. "They will never ask the aircraft to do something which could be inherently dangerous in such a fashion."
selected an altitude of 100 feet for three seconds on one occasion and chose the same altitude again for one minute, 47 seconds, another time, Quest said.
"What's he doing is he is testing the system," Quest said. "He is seeing how it reacts if you do something quite outrageous like set the autopilot to 100 feet instead of say 20,000 or 10,000 (feet) or whatever it is supposed to be.
"He wants to see, does the Airbus rebel? Does it set off warning noises? Does it take over control? Does the envelope protections suddenly kick in?" Quest said. "And what he discovers of course (is) it doesn't, and then on the return flight, we know what happens."
CNN aviation analyst Miles O'Brien
also agreed with the French authorities' report asserting that Lubitz practiced a course setting to crash the plane. Asked if there could be any innocent interpretation of the recorded events, O'Brien said, "It was a dry run, there's no question."
French authorities released details Wednesday of what happened on both the outbound and return flights aboard the Germanwings Flight 9525 between Barcelona, Spain, and Dusseldorf, Germany, in March.
It was on the return flight that Lubitz deliberately crashed
But it was on the outbound flight when Lubitz did test runs of changing the plane's altitude to 100 feet, the French authorities' report said.
was alone on the flight deck on the outbound flight, he was asked to bring the plane down to a lower altitude.
At one point, "the selected altitude decreased to 100 ft for three seconds and then increased to the maximum value of 49,000 ft and stabilized again at 35,000 ft," the report said.
Less than two minutes later, "the selected altitude was 100 feet most of the time and changed several times until it stabilized at 25,000 ft."
At this point the captain buzzed to re-enter the cockpit, and the flight continued as planned to Barcelona.
Because he had already been asked to descend, Lubitz's apparent rehearsal of different altitude settings would have gone unnoticed by air traffic controllers since he did not diverge from the flight plan.
The French investigators' report and a Germanwings representative both indicate that the same six crew members were on both legs of the trip.
The report by the French air accident investigation agency, the BEA, is based on analysis of the aircraft's flight data recorder and cockpit voice recorder.