The invention relates to an air duct (10) for supplying ambient air in an aircraft, comprising an air inlet (12), a flow duct portion (16) extending downstream of the air inlet (12) and a feed device (22) that is devised to feed ambient air through the air inlet (12) and the flow duct portion (16). A flow control flap (24) closes the air inlet (12) in a first position, releases a first flow cross-section of the air inlet (12) in a second position and releases a second flow cross-section of the air inlet (12), which is larger than the first flow cross-section, in a third position. The flow control flap (24) is so designed and disposed that a first surface portion (28) of the flow control flap (24), in the second position of the flow control flap (24), is aligned in the region of the air inlet (12) substantially parallel to an aircraft outer skin portion (18) is surrounding the air inlet (12), and that the first surface portion (28) of the flow control flap (24), in the third position of the flow control flap (14), is aligned in the region of the air inlet (12) at an angle to the aircraft outer skin portion (18) surrounding the air inlet (12).