On 28 January 2009 the commander of a Boeing 757-200 being operated by UK-based Operator Astraeus AL for Ghana Airways and acting as PF fir the sector became aware of a the failure of his ASI early in the night takeoff roll on a scheduled passenger flight. He decided to continue the takeoff and deal with the problem whilst airborne. After passing FL180 the crew selected the left Air Data switch to ALTN, believing this isolated the left Air Data Computer (ADC) from the Autopilot & Flight Director System (AFDS). Passing FL316, the VNAV mode became active and the Flight Management Computer™s (FMCs), which use the left ADC as their input of aircraft speed, sensed an overspeed condition and provided a pitch-up command to slow the aircraft. The co-pilot was concerned about the aircraft™s behaviour and, after several verbal prompts to the commander, pushed the control column forward. The commander, uncertain as to what was failing, believed that a stick-pusher had activated. He disengaged the automatics and lowered the aircraft™s nose, then handed over control to the co-pilot. A œMAYDAY was declared and the aircraft returned to Accra without further event.