Accident Overview
A Part 135 cargo flight conducting an ILS runway 27 approach at Helena Regional Airport collided with terrain during the procedure. The approach was performed in a non-radar environment. Although the published procedure requires maintaining 7,000 feet until intercepting the glideslope, the aircraft impacted the ground at an elevation of 5,300 feet about 1.5 miles before the point where the pilot should have crossed the Hauser NDB at an altitude of 6,741 feet.
Approach Procedure Details
According to the approach plate, the aircraft should not have descended below 5,400 feet until reaching the outer marker, which is located approximately 5.5 miles west of the impact site. The aircraft was executing a 'full' ILS approach, which includes a procedure turn to align with the final approach course.
Terrain and Weather Conditions
The accident site is characterized by hilly and mountainous terrain. Clouds were present in the area where the course reversal (procedure turn) was performed.
Official Probable Cause
The National Transportation Safety Board determined the probable cause of this accident to be the pilot's failure to maintain the correct altitude while turning inbound during a procedure turn to the ILS final approach course. Factors contributing to the accident included hilly/mountainous terrain and clouds in the area where the course reversal was performed.