The Germanwings co-pilot suspected of deliberately crashing a jet in the French Alps rehearsed the fatal manoeuvre on the morning of the disaster, and had twice been refused medical papers needed to fly, investigators have said.
The French BEA accident investigation agency said that on five occasions, the co-pilot set the autopilot to take the Airbus down to just 100 feet while the captain was out of the cockpit on the outbound flight to Barcelona from Duesseldorf.
But the brief twists of an altitude dial, mimicking those which crashed the A320 on its way back to the German city 2-3 hours later, would not have been noticed by passengers or controllers because they were quickly reversed and were masked by the fact that the jet had already started an authorised descent, the BEA said.
A preliminary report on the flight that crashed on March 24, killing 150 people, confirmed a growing picture of painstaking preparations carried out by the co-pilot, named by French prosecutors as Andreas Lubitz.
"All I can say is that he changed this button to the minimum setting of 100 feet and he did it several times," said Remi Jouty, director of the French BEA accident investigation agency. "These very brief actions were a sort of rehearsal of the manoeuvre."
Digging into data and cockpit recordings recovered from the jet's black boxes, the BEA gave the most detailed picture so far on what happened in the cockpit of return flight 9525.
Shortly after the A320 reached cruise height, the captain left the cockpit.
Just over 30 seconds after the door closed, leaving Lubitz alone, he entered the instruction he had rehearsed.
By turning a dial, he ordered the plane's autopilot to descend to 100 feet, the BEA said. This was the lowest setting possible and enough to crash into mountains ahead. He then altered another dial to speed the jet up.