What happened
The first officer was flying the aircraft during an instrument landing system approach to Salt Lake City (SLC). Fog seeding operations were active in the area, creating variable visibility conditions. The approach began with runway visual range well above Category I minimums.
At decision height, the captain called out "lights in sight." However, the first officer continued the descent through decision height. The aircraft re-entered instrument meteorological conditions, prompting the captain to call for a missed approach. The first officer applied power and established a wings-level attitude with a 10-degree nose-up pitch on the gyro horizon while the captain executed checklist items.
The captain then observed that the aircraft was heading 20 degrees right of course with a right-wing-down attitude on his gyro horizon. He called "turn left and pull up." The left main landing gear struck a 45-foot-high ILS antenna stack located 1,049 feet down the runway, 400 feet to the right of the centerline. This impact separated the left main gear. The aircraft diverted to Pocatello (PIH), where additional damage was sustained during landing.
The investigation
Post-accident testing revealed that the first officer's gyro horizon had bad bearings and its "off" flag was inoperative. Additionally, the first officer's altimeter read 100 feet high.