NYC06MA005 · Augusta 109E

The single-pilot helicopter was flying under instrument flight rules in night instrument meteorological conditions. The controller instructed the pilot to fly heading 340 degrees to intercept the localizer course for an instrument landing system approach. At that time, the helicopter was about 1.5 miles from the localizer centerline, headed 095 degrees, about 150 knots groundspeed. Consequently, the helicopter flew through and ended up well east of the 322-degree localizer course. During the resulting 135-degree turn to rejoin the final approach course, the pilot was issued an approach clearance, but told to "maintain 4,000." The helicopter's track approached the runway centerline, and then turned sharply away from, and to the right of the inbound course. The track showed an approximate heading of 100 degrees, when the radar target disappeared. During the 1 minute and 10 seconds following the pilot's acknowledgement 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 at that point of the flight, 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. The pilot had accrued 9,616 total hours of flight experience. He had 100 total hours of instrument flight experience; of which 10 hours was simulated instrument flight experience. 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.

Verbatim NTSB analysis and probable cause from the NTSB dataset