ERA17FA190 · Eurocopter Deutschland Gmbh EC 135 P2

The purpose of the flight was for the airline transport pilot of the helicopter to practice solo instrument approaches in instrument meteorological conditions (IMC). The pilot received adequate preflight weather briefings using company-approved weather sources, including one 35 minutes before departure. The terminal area forecast published earlier that morning and valid for the pilot's anticipated time of arrival at the destination indicated that the visibility would be 6 statute miles with an overcast ceiling at 1,200 ft agl; though the most recent surface observation report contradicted the forecast, indicating that the visibility was 4 statute miles in rain and the overcast ceiling was at 500 ft. The pilot subsequently submitted a flight request form to his company, which documented the weather products he reviewed before the flight and indicated that he was aware of the reported and the forecast weather conditions for the route before departure. The company's operation control center approved and released the helicopter for the flight. A review of weather radar and surface weather observation reports current at the time of the departure revealed that the helicopter entered and remained in IMC as it continued to the destination airport.

A review of radar data and air traffic control (ATC) communications revealed that controllers provided radar vectors to the pilot for an instrument landing system (ILS) approach. The helicopter intercepted the localizer course about 1 nautical mile (nm) outside the approach gate. The controller then cleared the pilot for the approach with a restriction to maintain an altitude at or above 2,000 ft mean sea level (msl), which was both the assigned altitude and the intermediate altitude for the approach, until established on the approach and to contact the control tower at the destination airport. The pilot acknowledged the clearance and contacted the tower controller shortly thereafter. After checking in with the tower controller; the helicopter maintained 2,000 ft msl as it continued through the glideslope and crossed over the locator outer marker, which had a published crossing altitude of 1,842 ft msl.

As the helicopter reached a point about 3 nm inside the outer marker, while flying at an altitude about 2,000 ft msl, the pilot declared a missed approach, telling the controller that he had received "some bad vectors at the very end" and that he wanted to "just line up and come back around again." The controller advised the pilot to fly the published missed approach procedure (a straight-ahead climb to 900 ft msl and then a left climbing turn toward the next navigational fix, at an altitude 2,000 ft msl). The helicopter then climbed straight ahead to an altitude of 2,525 ft msl in 9 seconds, before it turned right and started descending rapidly. The helicopter's calculated rate of climb before it began to descend was about 3,000 ft/min, while it's calculated groundspeed was about 120 knots. This climb rate and speed were not consistent with the pilot using the helicopter's automatic flight control system go-around mode because they were well above the climb rate and groundspeed that the "go around" mode would have maintained. Radar contact was lost as the helicopter descended through 1,625 ft msl, and the calculated descent rate between the helicopter's final two radar-recorded positions was more than 7,000 ft/min. No further communications were received from the pilot. One witness reported seeing the helicopter "spinning down…out of the clouds in an upside-down nose dive." Another witness reported that the helicopter descended "like a rocket" and that he did not observe any smoke or fire before the helicopter impacted the ground.

The helicopter came to rest in a ditch, fragmented and mostly consumed by postimpact fire, about 3,200 ft before the runway threshold. All the helicopter's major components were located in the wreckage area. Examination of the helicopter revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation.

The weather conditions recorded at the destination airport showed that IMC existed with easterly surface winds, visibility 2 1/2 statute miles in mist, an overcast ceiling at 500 ft agl, and temperature and dew point of 16°C. An AIRMET was current for low-level wind shear and turbulence for the region at the time of the accident, and high resolution rapid refresh model sounding data from around the time of the accident indicated that there was a possibility of turbulence. However, there was no verification of any significant wind shear or turbulence in any PIREPs, and the pilot did not report turbulence to air traffic control. Therefore, it could not be determined if turbulence contributed to the accident.

Although the radar vectors provided by the controller during the approach were contrary to the FAA's guidance to air traffic controllers, which required aircraft to be vectored to intercept an ILS localizer course 2 nm outside the approach gate given the weather conditions that prevailed at that time, radar data confirmed that the helicopter successfully tracked inbound toward the airport on the localizer course. Although the radar vectors did not directly contribute to the accident, they likely increased the pilot's task load during the accident sequence.

Several factors indicated that the pilot was task-saturated when the accident sequence occurred: he was performing an instrument approach that he had not previously performed; he was provided radar vectors close to the approach gate, which accelerated the timeline of the approach procedure; and he was likely already planning the return flight to the departure airport, which he previously indicated to the controller that he would conduct following the approach. That the pilot did not descend the helicopter after intercepting the glideslope or passing the final approach fix and did not fly the published missed approach procedure are indicative that he had likely become task-saturated during the final moments of the flight.

Nontime-correlated but sequentially recorded data recovered from the helicopter's warning unit revealed that, at some time during the accident flight, the greater-than-106% rotor rpm warning indicator illuminated multiple times, then the greater-than-112% rotor rpm warning illuminated. The rotor rpm warnings cycled between greater than 106% and 112% and less than 95% multiple times. Given that no discrepancies wiht the helicopter's engines or rotor system were discovered during the postaccident examination, it is likely that these rapid, dramatic changes in rotor rpm annunciated and recorded by the warning unit were the result of the pilot's control inputs as he became task-saturated and began to experience the effects of spatial disorientation. The helicopter's subsequent rapid climb, right turn contrary to the published missed approach instructions, and its near-vertical descent are consistent with the pilot's loss of helicopter control due to spatial disorientation.

Verbatim NTSB analysis and probable cause from the NTSB dataset