The concord didn't have an auxiliary power unit to provide energy with the engine off. So it needs to rely on energy from the gate or a special external unit. T

The concord didn't have an auxiliary power unit to provide energy with the engine off. So it needs to rely on energy from the gate or a special external unit. This unit was also necessary to provide the energy to start the engine. Obviously, it could start the engine but don't use them for taxiing, except that the 4 engines were so powerful that at idle produced enough thrust to move the plane (and they were burning a lot of gas). So better to taxi on it's on power than been towed. P.s: the 2 tons figure was the higher estimation, not the regular consumption...