Accident Details
A Part 135 cargo flight was conducting a full Instrument Landing System (ILS) approach to Runway 27 at Helena Regional Airport in a non-radar environment. The approach procedure requires the pilot to maintain an altitude of 7,000 feet until intercepting the glideslope. However, the aircraft struck the terrain at an elevation of approximately 5,300 feet. The impact occurred about 1.5 miles prior to the point where the pilot should have crossed the Hauser Nondirectional Beacon (NDB) at an altitude of 6,741 feet.
Flight Path
According to the approach plate, the aircraft was not authorized to descend below 5,400 feet until reaching the outer marker, which is located approximately five and one-half miles west of the impact site. The aircraft's descent below the published minimum altitude occurred well before intercepting the glideslope or reaching the outer marker.
Approach Procedure
The ILS approach to Runway 27 at Helena Regional Airport calls for a step-down altitude of 7,000 feet until glideslope interception. The Hauser NDB serves as a crossing fix at 6,741 feet. The outer marker, positioned about 5.5 miles west of the accident site, marks the point where descent below 5,400 feet is permitted. The aircraft's premature descent led to impact with terrain at 5,300 feet, which is below the minimum crossing altitude at the NDB and the outer marker altitude.
The investigation focused on the pilot's adherence to the published approach procedures in a non-radar environment, where no ground-based radar guidance was available to monitor the aircraft's altitude and position.