Incident Overview
A single-pilot helicopter operating under instrument flight rules (IFR) in night instrument meteorological conditions experienced a loss of radar contact after deviating from the assigned approach course. The controller had instructed the pilot to fly heading 340 degrees to intercept the localizer course for an instrument landing system approach. At the time of the instruction, the helicopter was approximately 1.5 miles from the localizer centerline, flying a heading of 095 degrees at a groundspeed of about 150 knots. This resulted in the aircraft flying through and ending up well east of the 322-degree localizer course.
Sequence of Events
During a subsequent 135-degree turn to rejoin the final approach course, the pilot was issued an approach clearance but was instructed to "maintain 4,000" feet. The helicopter's track initially approached the runway centerline, then turned sharply away to the right of the inbound course. The track showed an approximate heading of 100 degrees when the radar target disappeared.
In the 1 minute and 10 seconds following the pilot's acknowledgment of the 4,000-foot altitude assignment, the helicopter descended only 300 feet, slowed to approximately 65 knots groundspeed, and turned 140 degrees right of course. At the point where the helicopter re-intercepted the localizer, the autopilot was capable of capturing the localizer but incapable of capturing the glideslope. If altitude hold remained engaged and the pilot reduced collective to initiate a descent, the autopilot would adjust pitch in an effort to maintain the selected altitude. Similar scenarios in helicopters and flight simulators have resulted in unusual attitudes and zero airspeed descents to the ground.
Pilot Experience
The pilot had accrued 9,616 total hours of flight experience. He had 100 total hours of instrument flight experience, of which 10 hours were simulated instrument flight experience.
Wreckage and Communication Examination
Examination of the wreckage revealed no mechanical anomalies. Examination of voice communication tapes revealed that the controller used non-standard approach clearance procedures, did not comply with requirements for weather dissemination, and did not comply with the appropriate intercept angle of 45 degrees for helicopters as prescribed in Federal Aviation Administration orders.