Abstract: A flap door in the floor of an aircraft cabin has a mechanism for locking and unlocking the flap door from either side. A bearing block with a bellcrank lever pivoted to the block is attached to the flap door that hinges upwardly into the passenger cabin. The bellcrank lever is one-armed and has a lateral roller that engages into a lateral guide groove. Further, a locking member is provided on the one-armed bellcrank lever, which catches behind a spring biased stop member on the bearing block in the closed position of the flap door. A handle recessed in the upwardly facing surface of the flap door is connected through a flexible pull member for withdrawing the stop member out of its locking position to open the door from above.