É a porta de acesso do compartimento aviônico, conforme descrito no Manual de Operação da Tripulação de Voo !
An inward-opening, manually operated, hinged door gives access to the avionics compartment. This door is in the lower fuselage, forward of the nose landing gear bay. A ladder is stowed inside the compartment adjacent to this door, which may be either be operated from the interior or the exterior. This compartment is also accessible from the cockpit, via a floor hatch located behind the Captains' seat. A fixed ladder in the avionics compartment for access from the cockpit.
Aqui está um desenho do lado de fora!
E aqui uma vista da cabine de comando do cockpit para um A340!
