CEN16FA372

The pilot's excessive cyclic input during a missed approach maneuver in night instrument meteorological conditions, which resulted in a loss of control and spiraling descent into terrain.

The pilot and two medical crewmembers were conducting a night instrument flight rules cross-country flight to pick up a patient. During the instrument approach to the destination airport, the weather conditions deteriorated. The pilot was using the helicopter's autopilot to fly the GPS approach to the airport, and the pilot and the medical crew reported normal helicopter operations. Upon reaching the GPS approach minimum descent altitude, the pilot was unable to see the airport and executed a go-around. The pilot reported that, after initiating the go-around, he attempted to counteract, with right cyclic input, an uncommanded sharp left 45° bank . Recorded flight data revealed that the helicopter climbed and made a progressive right bank that reached 50°. The helicopter descended as the right bank continued, and the airspeed increased until the helicopter impacted treetops. The helicopter then impacted terrain on it's right side and came to rest near a group of trees. Postaccident examinations of the helicopter and flight control systems did not reveal any malfunctions or anomalies that would have precluded normal operation. The helicopter was equipped with a GPS roll steering modification that featured a switch that allowed the pilot to manually select the heading reference source. In case of a malfunction or an erroneous setting, the helicopter's automatic flight control system had at least two limiters in place to prevent excessive roll commands. Further testing revealed that the GPS roll steering modification could not compromise the flight director and autopilot functionalities to the point of upsetting the helicopter attitudes or moving beyond the systems limiters. Recorded helicopter, engine, and flight track data were analyzed and used to conduct flight simulations. The simulations revealed that the helicopter was operated within the prescribed limits; no evidence of an uncommanded 45° left bank was found. The helicopter performed a constant right climbing turn with decreasing airspeed followed by a progressive right bank with the airspeed and descent rate increasing. In order to recover, the simulations required large collective inputs and a steep right bank; such maneuvers are difficult when performed in night conditions with no visual references, although less demanding in day conditions with clear visual references. The data are indicative of a descending accelerated spiral, likely precipitated by the pilot inputting excessive right cyclic control during the missed approach go-around maneuver, which resulted in a loss of control.

Computed Tomography (CT) Scans The helicopter's control system actuators were subjected to CT scans to confirm internal component configuration and integrity without disassembly. The following actuators were scanned: roll trim actuator, both left and right roll linear actuators, and both left and right pitch linear actuators. The scans did not reveal any preimpact anomalies that would have precluded normal operation. The NTSB CT Specialist Factual Report is included in the public docket for this accident report. Actuator and Computer Testing The roll artificial feel and trim actuator were examined at the manufacturers facility under the supervision of the Agenzia Nazionale per la Sicurezza del Volo (ANSV) of Italy. Results of the examination showed that there were no mechanical or electrical malfunctions with the actuator and the unit passed its acceptance testing. The two helipilot computers and the FD computer were examined at the manufacturers facility under the supervision of the ANSV. The first helipilot computer sustained minor external damage, but there was no evidence of internal mechanical damage, or electrical/burn failures of the components located on the circuit boards or the circuit boards. All internal circuits were within specification. Control of the servo amplifiers output signal was confirmed with no anomalies noted. The test confirmed that the computer provided the correct command signal to position the linear actuators; the tests performed were successful and each pitch, roll, and yaw channel worked properly. Based on the results of the testing, no functional anomalies were found. The second helipilot computer sustained significant external damage and internal damage to the motherboard; the yaw, pitch, and roll cards were found separated from the motherboard due to the mechanical deformation of the chassis. The gain card was undamaged. Due to the internal damage, functional testing was limited to the roll and gain cards by using an exemplar chassis assembly. All internal circuits were within specification. Control of the servo amplifiers output signal was confirmed with no anomalies noted. The tests performed were successful and each pitch, roll, and yaw channel worked properly. Based on the results of the testing, no functional anomalies were found with the roll channel. The FD computer sustained significant external damage and the internal circuit cards were impact damaged but did not show signs of electrical/burn damage. A functional test of the FD computer could not be performed. The three main rotor actuators, identified as red, yellow, and blue, were examined at the manufacturers facility under the supervision of the ANSV. The red and yellow actuators attachments were fractured under overload. The actuators were subjected to the manufacturer's functional tests procedures; each actuator passed the functional tests and disassembly of the units was not performed. The results of the functional testing are provided in the NTSB Systems Factual Report included in the public docket for this accident report. Leonardo Helicopters (Agusta) Flight Simulation and Testing Leonardo Helicopters completed extensive flight simulations and testing based on the accident data. The simulator session was performed with an Agusta A109E level D full flight simulator (FFS) at the Leonardo Helicopter Training Academy, to reproduce the accident Flight and identify anomalies or contributing factors. An A109S FFS was not available, but the functionally of the A109E FD and helipilot computers are identical among the two simulator types. The testing revealed that the helicopter was operated within the prescribed limits and there was no evidence of a mechanical malfunction. The data revealed that the helicopter performed a constant right climbing turn with decreasing airspeed followed by a progressive right bank with airspeed and descent rate increasing. The simulator testing did not find evidence of an uncommanded 45° bank as reported by the pilot. The simulation required large collective inputs and steep right bank, which were the most critical conditions in the simulations, especially when performed in night conditions with no visual references. The simulation recovery maneuver was less demanding in day conditions with clear visual references. Further testing revealed that the GPS roll steering modification on an A109S cannot compromise the FD and AFCS functionalities up to the point of upsetting the helicopter attitudes. Data Collection Unit (DCU) Each engine is equipped with a DCU and both units were downloaded by the engine manufacturer under the supervision of the Transportation Safety Board of Canada. The purpose of the DCU is to serve as a repository for various engine parameters, accumulated operation time, accumulated part cycles, and specific operational exceedance data. The electronic engine controls automatically store the data in the DCU in snapshot format when there is a triggering event. Engine data stored during the last 100 hours of operating time was analyzed. Both engines were producing power at the moment of impact and no preimpact engine anomalies were recorded. Data Acquisition Unit (DAU) The DAU was examined and downloaded by the manufacturer under the supervision of the Federal Aviation Administration (FAA). The unit did not exhibit any significant impact damage and the download of both channels A and B was successful. The data was redundant from both channels and did not reveal any recorded faults or exceedances. Sandel ST3400 The Sandel ST3400 is an integrated Terrain Awareness and Warning System (TAWS). The device is capable of recording GPS coordinates, track, barometric altitude, vertical velocity, and radar altitude. The data retrieved from the device revealed an operating time from 01:25:54 to 02:03:42 CDT. On approach to AXN the device produced no voice callouts since the input from the radar altimeter never met the mandatory call-out threshold of 300 ft AGL. Additionally, there were no forward-looking terrain avoidance or ground proximity warning system alerts recorded in the flight data during the approach phase of the accident flight as the alerting buffer never indicated terrain and/or obstacle clearance issues. Appareo Stratus 2S The Appareo Stratus 2S is a battery-operated automatic dependent surveillance-broadcast (ADS-B) receiver with GPS capability designed to interface with an iPad, iPhone, or iPod Touch running the ForeFlight Mobile application. The device did not have any recorded data from the accident flight. Apple iPad Air 2 The iPad was found in the wreckage and displayed a map page within the ForeFlight application. The device was given to the operator and later sent to the NTSB Recorders Lab for download since the device was capable of storing non-volatile memory. When a download was attempted by the NTSB, the device had been manually reset and no data was retrieved. Garmin GNS 530 Data Card The data card was inserted into a surrogate Garmin GNS 530W unit at the NTSB Recorders Laboratory. When the device is powered using the docking station, the GPS is automatically put into a "simulator" mode; therefore, the map location shown on the screen was not indicative of any accident information. The map database was version 4.00 and the aviation database expiration date as October 13, 2016. When powered on, the device's communication (COM) frequency was set to 123.000 megahertz MHz and the localizer (LOC) frequency was set to 109.70 MHz. These frequencies corresponded to the pilot's statement that the last LOC frequency would have been selected for BRD instrument landing system (ILS) RWY 34 approach, which utilizes 109.7 MHz. At 0201, the AXN automated surface observing system (ASOS) recorded wind from 290 degrees at 10 knots, 9 miles visibility, scattered clouds at 400 ft, broken clouds at 3,600 ft, temperature 57 degrees F, dew point 57 degr