"Energy cannot be created or destroyed, it can only be changed from one form to another." - Albert Einstein
The EXPED push button is an optional feature offered by Airbus that lets pilots temporarily increase their climb or descent gradient at the touch of a button. With EXPEDite mode engaged during climb, the aircraft will soar skyward at Green Dot speed, (a slower speed which has the best lift to drag ratio. This converts the airplane’s speed (i.e. kinetic energy) into altitude (i.e. potential energy). It is worth knowing that green dot speed increases as an airplane gains altitude and it is not recommended using EXPED to climb above 25000ft (to avoid getting too close to stall speed).
During descent, pressing the EXPED button unleashes a high-speed, adrenaline-fueled plunge. The airplane changes its speed target to Mach 0.80 or 340kt, whichever is higher, enabling it to lose altitude at a breakneck pace while exchanging kinetic energy (Gaining speed) for potential energy (Losing altitude). It's like going on a thrilling roller coaster ride through the skies! So if you want to experience the rush of a speedy descent or a high-flying climb, the EXPED push button is the perfect tool to have in your arsenal.
In reality, however, this function is rarely used (pilots just use the speed knob to achieve the same purpose), hence with miniFCU, we have designed to enable it to swap with other more common functions like FS and LS.