Agusta Spa A109E N144CF accident near Eastland, Texas

Probable cause

The loss of helicopter control after an in-flight upset, which occurred when the pilot selected the autopilot’s altitude hold mode; the reason for the reported in-flight control anomaly could not be determined during postaccident helicopter examinations. Contributing to the accident was the pilot's delay in transitioning to instrument flight rules flight before entering instrument meteorological conditions.

NTSB analysis

The emergency medical service helicopter was dispatched on a 30-minute flight to pick up a patient at a hospital. Due to area weather forecasts of marginal visual meteorological conditions (VMC) to instrument meteorological conditions (IMC) conditions, the pilot had the flight dispatcher file an instrument flight rules (IFR) flight plan in the event that he had to execute an IFR approach at his destination. The first 20 minutes of the flight were conducted in VMC about 2,500 ft mean sea level (msl) and were uneventful. During the final 10 minutes of the flight, the helicopter was nearing IMC, which included high overcast and midlevel scattered to broken clouds with light to moderate rain showers and reduced visibility. The pilot began a climb to 4,000 ft msl and then contacted an air traffic controller to activate the IFR flight plan. During this time, both the flight paramedic and flight nurse told the pilot that they were not comfortable entering the worsening weather conditions. Upon reaching 4,000 ft msl, the pilot engaged the autopilot in altitude hold mode, and the helicopter then abruptly pitched down 90 degrees and began spinning with the airspeed increasing. The pilot identified a disagreement between the pilot and copilot attitude director indicators, turned the autopilot off, and moved his scan to the backup attitude director indicator. The pilot then attempted an unusual attitude recovery by initiating back pressure on the cyclic control; however, the helicopter continued to descend rapidly through the bottom of the cloud base very close to the ground. The helicopter subsequently touched down in a level attitude, bounced several times, and skidded to a stop. All three occupants were assisted from the wreckage by ground personnel.

Examination of the flight control systems did not reveal any anomalies that might have contributed to the accident. A review of the helicopter's maintenance history revealed that other company pilots had reported several occurrences of uncommanded pitch-and-roll anomalies with the helicopter during the previous several years. Maintenance inspections after these occurrences could not duplicate the reported problems, and the helicopter was always returned to service after successful flight control systems check flights. After the accident, the autopilot system, gyros, and servo components were examined, and no preimpact anomalies were found; however, the solid-state components could not be tested for functionality due to damage. The reason for the reported in-flight control anomaly could not be determined.

The flight paramedic and flight nurse said that they lost visual reference to the ground during the in-flight upset. Therefore, it is possible that the transition from VMC to IMC led to the pilot becoming spatially disoriented while he was trying to recover from the reported upset and that this prevented him from recovering from it; however, investigators could not definitively determine if the pilot became spatially disoriented. Regardless, it is likely that an earlier transition from VFR to IFR flight before encountering IMC would have given the pilot a better chance to recover from the reported autopilot system-induced anomaly and would have reduced the possibility of his becoming spatially disoriented.

Text from the NTSB. Open the NTSB docket for CEN12FA670 for the full record.