What happened
During a scheduled cargo operation, a Part 135 aircraft was conducting a full ILS approach to runway 27 at Helena Regional Airport. The flight was operating in an environment without radar coverage. While executing the procedure turn to intercept the final approach course, the aircraft descended below the required altitude prescribed by the approach charts.
The flight profile required the crew to remain at 7,000 feet until the glideslope was intercepted. However, the aircraft struck the ground at an elevation of approximately 5,300 feet. This impact occurred roughly 1.5 miles before the aircraft would have reached the Hauser NDB, a waypoint where the altitude should have been 6,741 feet. Per the established approach instructions, the aircraft was not permitted to descend below 5,400 feet until reaching the outer marker, which was situated approximately five and one-half miles west of the crash site.
Findings
Investigations into the accident determined that the primary factor was the pilot's failure to maintain the prescribed altitude while turning inbound toward the final approach course. The descent occurred during the course reversal phase of the instrument approach. Environmental conditions at the time of the accident included mountainous terrain and cloud cover, which complicated the execution of the procedure turn.