How many airbrake panels deploy in AB1 mode?

In AB1 mode of the Dassault Falcon 2000LXS, one airbrake panel deploys. This configuration is primarily used to assist in reducing airspeed during descent or approach while maintaining control. The deployment of a single panel helps manage drag without significantly affecting the airplane's handling characteristics, allowing for more precise control during critical phases of flight. This design decision ensures that pilots have the ability to modulate deceleration effectively and maintain an optimal descent profile without overwhelming the aircraft with too much drag.

Other options misrepresent the actual function of the airbrakes in AB1 mode. Having no panels deploy would negate the purpose of airbrakes, which is to increase drag. If two or three panels were to deploy, that would lead to excessive drag, which is not desirable during standard operations. Hence, the selection of one airbrake panel gives a balanced approach to deceleration while providing adequate control.