Serious incident to the Learjet 45 registerd D-CNMB on 18/12/2019 en route [Investigation delegated to STSB / Switzerland by the BEA]

Preliminary data based on the notification from the Swiss authorities:

At cruising level, an alarm for aileron mistrim is triggered. As the pilots complete the appropriate checklist, manual roll control becomes very difficult to handle and a distress message (MAYDAY) is declared to air traffic control. The flight crew decided to divert to Geneva Airport (LSGG), where they were able to carry out a safe landing with the flaps retracted.