Incident Overview
An aircraft executing an Instrument Landing System (ILS) approach experienced a left wing strike during the flare phase, resulting in substantial damage. The incident occurred after the aircraft accumulated ice on the leading edges of the wings during the final stages of the approach.
Approach and Ice Accumulation
The aircraft initially commenced a full ILS approach to the Spokane area but terminated it approximately 200 feet above the decision height, executing a missed approach. Air traffic control then vectored the aircraft for a second ILS approach. During the last 400 feet of this approach, the aircraft accumulated between three-quarters and one inch of mixed rime and clear ice. The copilot visually identified the approach lights, and the crew continued the ILS to landing. During the flare, the left wing dropped and struck the runway, causing substantial damage. Post-incident examination revealed that ice had formed on the leading edges of the wings in a flat plane of about two inches, perpendicular to the chord line.
Fog Dispersal Operations
At the time of the incident, fog dispersal operations were in effect. This procedure involved the use of aircraft to disseminate dry ice into the fog to provide condensation nuclei, thereby increasing fog droplet size to promote dissipation. The process also reduces the temperature of the surrounding air and, in certain conditions, can attribute to airframe icing. The prevailing temperature was 33 degrees Fahrenheit.