What emergency exit does the flight deck use if the MCD is blocked?

The flight deck's designated emergency exit in the event of a blockage at the Main Cabin Door (MCD) is the crew escape hatch. This hatch is specifically designed for emergency situations, allowing the flight crew to exit swiftly and safely if the primary exit is inaccessible. Its location and design facilitate a quick exit while minimizing risks associated with other potential exit routes.

The other options, while they may serve as exits in various scenarios, are not specifically meant for situations where the MCD is blocked. The side door exit, emergency exit slide, and rear service door may not be as operationally effective or safe for the flight crew in the context of an emergency where a rapid and secure egress is required, which is why the crew escape hatch is the correct choice.