If icing didn't bring Colgan down, what did?

By David Learmount

If icing now looks likely not to have been the only cause of the Colgan Air Bombardier Dash 8 Q400 accident, the investigators have to consider what other factors were involved.

The possibilities include the fact that because the crew were aware they were in icing conditions they raised their workload and may have been hyper-sensitive to non-standard aircraft behaviour - like the operation of the stick shaker/pusher. In addition, all the problems happened at about the time the aircraft was intercepting the ILS localiser and, a little later, the glideslope. This high workload process can distract the crew's attention from critical performance issues like airspeed monitoring. Even small amounts of ice contamination on flying surfaces such as the wings and tailplane can alter their stalling angles of attack and also move the centre of lift, usually forward.