What happened
A scheduled passenger flight was conducting an instrument landing system (ILS) approach when the aircraft encountered freezing fog. The crew reported receiving an ice caution message almost immediately upon entering the fog layer. Although the crew activated wing and engine inlet anti-ice systems, ice accumulated rapidly on the windshield wipers and the winglet.
During the approach, visibility was reported at one-half mile. As the aircraft approached minimums, the captain regained visual contact with the runway at approximately 140 feet above the ground. The first officer disconnected the autopilot, causing the nose to pitch up slightly. The captain instructed the first officer to maintain a nose-down attitude and increase thrust. As the aircraft drifted right of the centerline, the captain took control, noting that the aircraft felt heavy and sluggish.
Upon adding thrust, the ailerons became more responsive, but the left wing dropped and scraped the runway at approximately the same time the left main gear touched down. The CL-600 then bounced into the air before landing hard on the runway. The crew taxied the aircraft to the gate. There were no fatalities or injuries.
The investigation
An inspection of the aircraft and airport the following afternoon revealed ice accumulation on the antennas, windshield wipers, radome, winglets, and both horizontal and vertical stabilizers. The ice thickness was measured between one-half to five-eighths of an inch, with total thickness including ice spines reaching three-quarters of an inch.
Kinematic parameter extraction indicated a loss of lift consistent with airframe icing; however, the data showed no early stall prior to touchdown and no indication that icing caused the loss of control. Flight data recorder analysis showed the aircraft rolled left and then right when the autopilot was disengaged. The aircraft initially touched down 1,976 feet from the approach end of the runway with the right main gear in the grass. The left wing tip left a 63-foot scrape mark on the runway. The aircraft experienced a vertical acceleration of at least 1.8g during the initial touchdown and a subsequent 3.25g impact one second later.