Heavy load carrier comprising a base and peripherally arranged side walls (2, 4, 6, 8), at least one of the side walls having a flap which seals a flap opening in the side wall in a closed position and is transferable by pivoting into an open position in which the flap is flapped against the side wall from the outside, the flap being articulated to the side wall by coupling elements, the coupling elements being articulated to the side wall by side wall joints and to the flap by flap joints, and at least one forced guide (28, 34, 42) for the flap being provided and, when the flap is pivoted, simultaneously bringing about a translational flap movement in the plane of the flap, in such a way that the flap is moved upwards towards the upper edge of the side wall when the flap opening is closed, the forced guide being arranged on each of two lateral edges (38, 40) of the flap opening and of the flap and comprising at least one first run-up ramp (34, 44) arranged on the side wall or the flap, a first run-up ramp being formed on each of the lateral edges (38, 40) of the flap opening and cooperating with a first projection on each of the two lateral flap edges, or there being a kinematically reversed arrangement, characterised in that the first run-up ramp is in each case formed in such a way that after travelling over a ramp the flap moves translationally towards the base under gravity and/or a spring bias, a spring being arranged on each of the lateral edges (38, 40) of the side wall which delimit the flap opening and being biased towards closing the flap in such a way that the flap is held in a locking position, the spring being tensioned vertically upwards, resulting in an upward bias, or being pressed horizontally towards the flap interior, resulting in an outward bias, when the flap enters the closed position. the flap being articulated to the side wall by coupling elements, the coupling elements being articulated to the side wall by side wall joints and to the flap by flap joints, and at least one forced guide (28, 34, 42) for the flap being provided and, when the flap is pivoted, simultaneously bringing about a translational flap movement in the plane of the flap, in such a way that the flap is moved upwards towards the upper edge of the side wall when the flap opening is closed, the forced guide being arranged on each of two lateral edges (38, 40) of the flap opening and of the flap and comprising at least one first run-up ramp (34, 44) arranged on the side wall or the flap, a first run-up ramp being formed on each of the lateral edges (38, 40) of the flap opening and cooperating with a first projection on each of the two lateral flap edges, or there being a kinematically reversed arrangement, characterised in that the first run-up ramp is in each case formed in such a way that after travelling over a ramp the flap moves translationally towards the base under gravity and/or a spring bias, a spring being arranged on each of the lateral edges (38, 40) of the side wall which delimit the flap opening and being biased towards closing the flap in such a way that the flap is held in a locking position, the spring being tensioned vertically upwards, resulting in an upward bias, or being pressed horizontally towards the flap interior, resulting in an outward bias, when the flap enters the closed position. that the first run-up ramp is in each case formed in such a way that after travelling over a ramp the flap moves translationally towards the base under gravity and/or a spring bias, a spring being arranged on each of the lateral edges (38, 40) of the side wall which delimit the flap opening and being biased towards closing the flap in such a way that the flap is held in a locking position, the spring being tensioned vertically upwards, resulting in an upward bias, or being pressed horizontally towards the flap interior, resulting in an outward bias, when the flap enters the closed position.