This is really strange (flight to BCN)
On the previous flight, the following facts can be noted:
at 7 h 19 min 59, noises like those of the cockpit door opening then closing were recorded and corresponded to when the Captain left the cockpit; the aeroplane was then at cruise speed at flight level FL370 (37,000 ft);
at 7 h 20 min 29, the flight was transferred to the Bordeaux en-route control
centre and the crew was instructed to descend to flight level FL350 (35,000 ft), an instruction read back by the co-pilot;
at 7 h 20 min 32, the aircraft was put into a descent to flight level FL350 , selected a few seconds earlier;
at 7 h 20 min 50, 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;
at 7 h 21 min 10, the Bordeaux control centre gave the crew the instruction to
continue the descent to flight level FL210;
at 7 h 21 min 16, the selected altitude was 21,000 ft;
from 7 h 22 min 27, the selected altitude was 100 ft most of the time and changed several times until it stabilized at 25,000 ft at 7 h 24 min 13;
at 7 h 24 min 15, the buzzer to request access to the cockpit was recorded;
at 7 h 24 min 29, noises like those of the unlocking of the cockpit door then its opening was recorded and corresponded to the Captains return to the cockpit;
at 7 h 25 min 32, the flight was transferred to the Barcelona en-route control
centre and the crew was instructed to descend to FL170;
at 7 h 26 min 16, the aircraft was put into a descent to its newly cleared flight level and the flight continued normally.
Due to the engaged autopilot modes, the changes in selected altitudes described above did not influence the aircraft descent flight path.
On page 28 of the final report you can find the corresponding graph, scary.
https://www.bea.aero/uploads/tx_elyd...0125.en-LR.pdf