The interlock between the wing sweep lever and Flap lever in the throttle box was mechanical, the exception was the manoeuvre Switch, however the control mechanism covering that relied on the feedback shafts between the flap/slat drive unit and the wing sweep actuators to the High lift and Wing Sweep Control Unit, all instances of the Flaps going into the side of the fuselage were due to the FSDU to HLWSCU feedback shafts not being connected, so the electrical position indicator on the RH side of the HLWSCU would have no idea of the incorrect positions so the electrical/hydraulic interlock would also not engage. If memory serves the first one occurred at Cottesmore, the second at Marham (might be the other way around) and I don’t recall a St Athan one and both the flaps were down but the lever had been moved to the up position whilst power was off, with power supplied the wing sweep lever was able to be moved as the mechanical interlock was not engaged.
High lift devices A three-section slat is installed in the wing leading edge. Each slat section is equipped with two tracks which slide over rollers fitted to the wing leading edge. The three sections are mechanically linked to each other and are moved by four screw jacks. A four-section double-slotted flap is fitted along the full trailing edge of each wing. Each section consists of a main vane and a leading edge vane fixed to the main vane. The actuation system is comprised of eight screw jacks, two for each vane. The actuation system is driven by units located in the centre fuselage, which is powered by four hydraulic motors – two motors driving the flap system and two driving the slat system. Hydraulic power is supplied by both hydraulics systems, each powering one slat and one flap motor. When a hydraulic failure occurs, the motors powered by the functioning system are still able to drive both flaps and slats to their full travel. As long as the wings are selected fully forward, the flaps lever may be moved to any of its three positions (UP, MID and DOWN). In addition to the UP, MID and DOWN positions, the flaps and slats can be extended to a manoeuvre position. With the wings swept to 25° the flaps can be extended to 7° and the slats to 11°. With the wings swept to 45° the slats can be extended to 11°, whilst the flaps remain retracted. The manoeuvre flaps and slats are selected by operation of the combined airbrakes/ manoeuvre, flap/slat switch