Medevac Helicopter Crashes With Patient Onboard

On July 7, 2018, about 2123 CDT, a Eurocopter Deutschland GMBH EC135 P1 helicopter, N312SA, impacted terrain during an autorotation near Chicago, Illinois. The pilot, paramedic, and nurse were seriously injured, and the patient was not injured. The helicopter was operated by Pentastar Aviation Charter as an air ambulance flight.
While en route, the pilot noticed a twist grip caution indication on the left engine (No. 1) cockpit display system (CDS) panel. The pilot also noticed a second indication but could not recall the specific caution. He stated that he then grabbed each engine throttle twist grip individually to gently verify if he could feel they were in or out of neutral detent, but did not notice any significant changes to the throttle position. The pilot decided to divert to a nearby airport, and, as he executed a turn toward the airport, he noticed the No. 2 engine indication no longer matched the No. 1, stating that "it was lower and oscillating."
Within ~1 minute, the pilot "heard the low rotor [rpm] horn," and lowered the collective to maintain rotor speed. The pilot located a "dark spot" on the ground, which he determined would give him the best opportunity to complete a full autorotation. As he started a turn toward his intended landing location, he felt the tail oscillate to the right and back and heard an oscillation in engine speed. When the helicopter was about 200' AGL, he thought he may land short of the intended location and adjusted the collective and cyclic to maintain rotor rpm and airspeed. The helicopter impacted terrain, rotated 180°, and came to rest upright. This video from a rail platform showed a fire near the right (No. 2) engine during the autorotation, and a flame burst after impact with terrain.
Examination of the aircraft revealed no evidence of pre-impact mechanical malfunctions or failures that would have precluded normal operation. Analysis of data retrieved from the CDS and EEC units revealed that, about 4 minutes after takeoff, the No. engine was placed in manual mode and out of EEC control, which indicates that the pilot had likely inadvertently moved the No. 1 engine throttle out of its neutral detent. The No. 2 engine was in manual mode for about 7 minutes before the pilot noted the CDS twist grip caution indication. The data showed that as the pilot continued to manually control the No. engine, the No. 2 engine was also placed in manual mode and out of EEC control, which indicates that the pilot moved the No. 2 throttle out of its neutral detent. The pilot attempted to maintain rotor and engine rpms while controlling both engines manually; it is not likely that he fully understood the nature of the problem.
The pilot misinterpreted an aural alert (low rotor rpm as opposed to high rotor rpm) when high rotor rpm existed, then lowered the collective, which created a rotor overspeed condition. This configuration resulted in a high-workload scenario in which it would be particularly challenging for the pilot to control the helicopter while maneuvering in low altitude and night visual conditions.
The pilot had accumulated about 300 hours in EC135s, with about 11 hours in the accident make and model. The accident helicopter was the only EC135 P1 variant in the operator's fleet. Its engines, displays, and throttle controls differed from the EC135 P2+ in which the pilot was formally trained. The pilot had completed an online self-study differences training presentation, and some informal familiarization training with other company pilots. No formal training was part of the differences training curriculum.
Because the throttle (twist grip) differs between the P1 and P2+ variants, it is likely that the pilot moved it into manual mode without realizing; he likely did not recognize this issue because he did not have as much experience or formal training in the P1 variant. Because the displays also differed between the variants, it could have been more difficult for the pilot to recognize and understand the indications he was receiving. Given the differences among the two variants regarding the displays and throttle controls, additional familiarization training, such as a familiarization flight with a company check pilot, would have provided the pilot with a better understanding of the key differences.
The helicopter manufacturer issued a voluntary service bulletin 10 years before the accident regarding collective throttle controls with grips that had an increased mechanical protection against unintentional adjustment.
The NTSB determined the probable causes of this accident to be the pilot's inadvertent disabling of the No. 1 and No. 2 engines' electronic engine control systems, which resulted in engine and rotor overspeed conditions, a subsequent autorotation, and a a hard landing. Contributing to the accident were the pilot's inexperience with the helicopter variant and the operator's lack of a more robust helicopter differences training program.