Serious incident to the Cessna 525 registered F-HJAV operated by Valljet on 14/03/2025 near Paris-Le Bourget AD

The crew took off from Limoges-Bellegarde airport at 17:55 bound for Paris - le Bourget airport.

When flying through the transition altitude, the pilots detected an inconsistency between the altitude values indicated on their PFDs.

When the aeroplane was established at FL 180 according to the information displayed on the captain’s PFD , the crew informed ACC/south-west air traffic control that they had an on-board altimeter problem. The crew indicated to the controller that they were at FL 180 and asked him to confirm the flight level displayed on the radar screen. The controller informed the crew that they were displayed as being at FL 180.

Thereafter, the processing of the failure led the crew to consider that the indicated altitude on the co-pilot’s PFD was erroneous. The crew thus selected ADC 1  as the altimetric source for both PFDs.

At around 18:30, the crew began the descent. Five minutes later, when the crew thought they had started level flight at FL 90 and were trying to contact the CDG controller, the GNSS altitude was in reality of the order of 3,000 ft in descent with a vertical speed of around -270 ft/min.

In their statements, the crew specified that a PULL UP TERRAIN TAWS warning was activated afew minutes later. At this point, the aeroplane, supposed to be at FL 90, was at a GNSS altitude of approximately 1,200 ft, i.e. a height of approximately 700 ft, in descent. The captain disconnected the autopilot, increased power and flew using external visual references.

The crew landed at Le Bourget airport at 18h58.