germanwings memorial service
German President Joachim Gauck is pictured on a video screen outside Cologne Cathedral during a memorial service for the 150 victims of Germanwings flight 4U 9525 in Cologne, April 17, 2015. Germany holds a state ceremony at Cologne cathedral to remember the dead killed in the March 24 Germanwings plane crash in the French Alps. Reuters/Wolfgang Rattay

Germanwings co-pilot Andreas Lubitz rehearsed a controlled descent on another flight on the day he is believed to have deliberately crashed Flight 9525 in the French Alps, investigators said Wednesday. A preliminary report by France's BEA investigation agency, citing cockpit data, stated that on both flights the pilot had left the cockpit.

Lubitz put the plane into descent mode five times in a four-and-half-minute period on the Airbus A320 jet's trip from Duesseldorf to Barcelona on March 24, the BEA said in its preliminary report. On the return flight from Barcelona to Duesseldorf, Lubitz is believed to have locked the captain out of the cockpit and plunged the plane into an early descent. However, authorities could not determine the reason behind Lubitz's action from the cockpit data.

“Several altitude selections towards 100 ft were recorded during descent on the flight that preceded the accident flight, while the co-pilot was alone in the cockpit,” French investigators said, in the report.

The BEA said it is continuing to look at the "systemic failings that may have led to this accident or similar events." The probe will focus on the medical aspects and cockpit security, and "seek to understand the current balance between medical confidentiality and flight safety,” the report added.

The crash killed all 150 people on board, including Lubitz. A separate criminal investigation into the crash is being conducted by French prosecutors.

“The initial information from the investigation shows that, during the cruise phase, the co-pilot was alone in the cockpit. He then intentionally modified the autopilot instructions to order the aeroplane to descend until it collided with the terrain. He did not open the cockpit door during the descent, despite requests for access made via the keypad, the cabin interphone and knocks on the door,” the BEA report stated.

A transcript of the Airbus A320’s cockpit voice recorder, published by Bild in March, had revealed Captain Patrick Sondenheimer shouting, "Open the goddamn door," as he tried to break into the locked cockpit. A conversation between the captain and Lubitz -- shortly after the flight took off from Barcelona for Duesseldorf -- indicated that Lubitz had encouraged Sondenheimer to use the toilet.

"During the descent of the accident flight, the Marseille control centre called the flight crew on eleven occasions on three different frequencies, without any answer being transmitted," the latest BEA report stated, adding that the French military defense system also tried to contact Flight 9525, which goes by the call sign GWI18G, on "three occasions during the descent, without any answer."

Authorities had earlier said that Lubitz had been suffering from depression and had been treated for psychological problems. Last month, German prosecutors also said that the 27-year-old had researched suicide methods and the security of cockpit doors.

"An episode of depression and the taking of medication to treat it delayed the renewal of the copilot’s class 1 medical certificate between April and July 2009," the BEA report stated Wednesday, adding: "The Captain’s and co-pilot’s training files show that their professional level was above standard."