History of Flight
On September 17, 2016, at 0204 central daylight time, an Agusta (Leonardo) A109S helicopter, registration N91NM, impacted trees and terrain near Chandler Field Airport (AXN) in Alexandria, Minnesota. The commercial pilot and two crew members sustained serious injuries, and the helicopter was destroyed. The aircraft was operated by North Memorial Air Care under 14 CFR Part 135 as an air medical positioning flight. Night instrument meteorological conditions prevailed, and an IFR flight plan had been filed. The helicopter departed Brainerd Lakes Regional Airport (BRD) at 0137, destined for the Douglas County Hospital helipad via AXN.
Air traffic control communications and radar data indicated that the pilot requested a clearance at 0135 and departed shortly thereafter. The helicopter climbed to 4,000 ft AGL and flew southwest. The pilot contacted ATC and requested to proceed direct to KILVE, the initial approach fix for the RNAV (GPS) approach to runway 22 at AXN. The controller cleared the approach and instructed the pilot to maintain 4,000 ft until established. Radar contact was lost one minute later. Ten minutes later, the pilot reported inbound at KILVE. The controller approved a frequency change and requested cancellation of the IFR flight plan; no further communications were recorded. Radar data showed the helicopter remained on the final approach course descending until the last target at 0201:06, 4.75 nautical miles from the runway at about 2,050 ft AGL.
In a postaccident statement, the pilot stated that he accepted the flight after reviewing weather conditions and filed an IFR flight plan. About 20 miles from AXN, he noticed clouds forming beneath the helicopter. He initiated a missed approach using the go-around function of the autopilot with 100% engine power. During the missed approach, the helicopter made a quick 45° left bank, and he applied right cyclic, then the helicopter banked sharply to the right.
The flight nurse seated in the middle cabin stated that the IFR flight was uneventful until near the airport. He could see runway lights through the fog but could not determine altitude. The pilot told the crew they would go-around. The helicopter banked right, then shuddered when alarms sounded. The engines sounded normal throughout.
The helicopter impacted the tops of several tall trees and the ground, continuing into a wooded area. Several residents heard the engines and impact.
Recorded flight data showed the flight path aligned with the GPS approach course, intercepting the last waypoint WANBI at 02:02:31, then deviating right of course. The helicopter reached the minimum descent altitude of 1,840 ft at 02:03:12. Between 02:03:12 and 02:03:14, collective position increased, consistent with a go-around. The helicopter descended to 1,740 ft until a climb began at 02:03:17, climbing and turning right with a maximum bank angle of 50°.
Personnel Information
The pilot was the Director of Operations for North Memorial Air Care. In the preceding 6 months, he had accumulated 2.4 hours of flight time in actual instrument conditions, logged 11 precision instrument approaches, and 6 landings at night. The North Memorial Operations Manual required pilots to comply with 14 CFR Part 135.247(a)(2) for recent night flight experience; the pilot had logged 6 night takeoffs and landings in the preceding 90 days.
Aircraft Information
The helicopter was equipped with a Spectrum Aeromed Medical Conversion Kit (STC SR02974CH) as of June 12, 2015. It had a GPS roll steering modification featuring a HEADING/GPS STEER switch. In HEADING mode, the flight director calculates roll commands to maintain a selected heading. In GPS STEER mode, the flight director receives a heading error signal from a dedicated STC box. The automatic flight control system includes limiters to prevent excessive roll commands: a maximum roll command of ±20° in HDG mode, and a maximum roll attitude of ±24° and roll rate of ±8.2° per second in the helipilot computers.
Meteorological Information
At 0201, the AXN ASOS reported wind from 290° at 10 knots, visibility 9 miles, scattered clouds at 400 ft, broken clouds at 3,600 ft, temperature 57°F, dew point 57°F, altimeter 29.87 inHg. At 0209, visibility dropped to 4 miles with mist and broken clouds at 300 ft. An AIRMET Sierra for IFR conditions due to mist and precipitation was issued on September 16 at 2145 and was valid at the accident time.
The pilot used the ForeFlight application on his iPad at 0119 and received a Lockheed Martin Flight Service weather briefing. The briefing contained all valid AIRMETs, observations, and forecasts. No record of other weather information was found.
Wreckage and Impact Information
The accident site was in a residential area about 1,000 yards northwest of the approach end of runway 22 at AXN. The debris path was about 130 yards long, beginning with lopped treetops (95-100 ft tall) and ending 30 yards beyond the main wreckage. Initial impact marks included parallel ground scars and the tail skid in an impact crater. The fuselage came to rest on its left side, separated aft of the engines, and wrapped around two trees. The right side showed ground impact damage and mud smearing. The tail section was oriented opposite the fuselage, with mud smearing near the tail rotor. The right pilot seat and one passenger seat pan had separated from their mounts.
Postaccident examination found no malfunctions or anomalies in the flight control and autopilot system. The HEADING/GPS STEER pushbutton was found in the HEADING position, and electrical continuity was confirmed. Depressing the button confirmed GPS STEER function.
Tests and Research
Both engine data collection units were downloaded. Engines were producing power at impact, with no preimpact anomalies. The data acquisition unit showed no faults or exceedances. The Sandel ST3400 TAWS recorded no voice callouts because radar altitude never met the 300 ft AGL threshold, and no terrain or obstacle alerts were recorded. The Appareo Stratus 2S had no recorded data from the accident flight. The iPad was manually reset and no data was retrieved. The Garmin GNS 530 data card displayed frequencies corresponding to the pilot's statement about the BRD ILS approach.
CT scans of control system actuators revealed no preimpact anomalies. The roll artificial feel and trim actuator passed acceptance testing. The helipilot computers passed functional tests, though one had minor external damage. The flight director computer could not be tested due to impact damage. The three main rotor actuators passed functional tests.
Leonardo Helicopters conducted flight simulations using an A109E simulator (functionally identical to A109S) to reproduce the accident. Testing found no evidence of an uncommanded 45° bank as reported by the pilot. The simulation required large collective inputs and steep right bank, which were most critical in night conditions with no visual references. Recovery was less demanding in day conditions. Further testing showed that the GPS roll steering modification could not compromise the FD and AFCS functionalities to upset helicopter attitudes.