Chicago, IL, USA
N312SA
EUROCOPTER DEUTSCHLAND GMBH EC135 P1
While en route during night visual conditions to a hospital helipad with two crewmembers and a patient, the commercial 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 message. 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 position (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 engine indication; he stated that "it was lower and oscillating." Within about 1 minute of the turn, the pilot "heard the low rotor [rpm] horn," and he 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 increase and decrease in engine speed. When the helicopter was about 200 ft above ground level, 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. Surveillance video from a rail platform near the accident site showed a fire near the right (No. 2) engine during the autorotation and a flame burst after the impact with terrain. Examination of the throttles, throttle linkages, engines, control systems, CDS, and the electronic engine control (EEC) units revealed no evidence of preimpact 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. 1 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. 1 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. 1 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 and 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 of flight experience in EC135s, with about 11 hours in the accident make and model EC135 P1. 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+ variant in which the pilot was formally trained. The investigation revealed the pilot completed a basic online (self-study) differences training presentation and some informal familiarization training with other company pilots. No formal flight 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 it; 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 service bulletin about 10 years before the accident regarding collective throttle controls with grips that had an increased mechanical protection against unintentional adjustment; however, that modification was not mandatory.
HISTORY OF FLIGHTOn July 7, 2018, about 2123 central daylight time, a Eurocopter Deutschland GMBH EC135 P1 helicopter, N312SA, impacted terrain during an autorotation near Chicago, Illinois. The pilot, flight paramedic, and flight nurse sustained serious injuries, and the patient was not injured during the accident. The helicopter sustained substantial damage to the fuselage, tailboom, and main rotor blades. The helicopter was registered to Bennett Aviation, LLC, Elmhurst, Illinois, and operated by Pentastar Aviation Charter under the provisions of Title 14 Code of Federal Regulations (CFR) Part 135 as an air ambulance flight. Night visual meteorological conditions prevailed at the time of the accident, and the flight was operated under a visual flight rules flight plan. The flight departed St. Mary Medical Center, Hobart, Indiana, at 2110, and was destined for Advocate Christ Medical Center, Oak Lawn, Illinois. Helicopter satellite tracking data and air traffic control information revealed the helicopter was traveling northwest from the St. Mary Medical Center on a direct route to Advocate Christ Medical Center about 1,000 ft above ground level (agl). About 5 miles southeast of Advocate Christ Medical Center, the helicopter turned to the right after the pilot requested to divert to the Gary International Airport (GYY), Gary, Indiana. About a minute later, the pilot declared a "mayday" and stated the helicopter was going down into a field. The helicopter came to rest upright in a grass area between the Interstate Highway 94 and Interstate Highway 57 interchange (see Figures 1, 2, and 3). Figure 1. Flight Track Map Figure 2. Main Wreckage Figure 3. Main Wreckage Surveillance video from a Chicago Transit Authority rail platform, located adjacent to the accident site, depicted the helicopter during the final phase of the autorotation and impact with terrain. The video showed a fire near the No. 2 (right) engine during the autorotation. A flame burst was observed after the impact with terrain. The pilot was able to recall portions of the flight and recounted them during interviews with National Transportation Safety Board (NTSB) investigators and also provided a written statement. On the evening of the accident, the pilot received a flight request, checked the weather, and performed a preflight inspection for the planned 12 to 13-minute flight. After departure, the pilot climbed to 1,700 ft mean sea level, or about 1,000 ft agl. About 5 miles west of GYY, he contacted Chicago Midway International Airport (MDW), Chicago, Illinois, requesting entry into the airspace, and noticed a "Twist Grip" warning on the left engine 1 side warning panel. The pilot noticed a second indication but could not recall the specific warning. He grabbed each engine throttle twist grip individually to gently verify if he could feel they were in or out of position, and he did not notice any significant changes to the throttle position. The pilot decided he did not have enough time to trouble shoot the emergency procedure before landing at the intended hospital destination, and he would not land at the hospital with a warning indication. He informed the medical crew they would divert to GYY and handed them the helicopter emergency checklist book to assist with locating the emergency checklist procedure(s). As the pilot executed the turn to GYY, he noticed the No. 2 engine indication (N1 gas producer) no longer matched with the No. 1 engine; "it was lower and oscillating." Within about 1 minute of the turn toward GYY, the pilot "heard the low rotor RPM horn", and he lowered the collective to maintain rotor speed. The pilot located a "dark spot" which would give him the best opportunity to complete a full autorotation with a flare to cushion the landing. The pilot determined he no longer could troubleshoot the problem and was doing his best to fly the helicopter. As he started a turn toward his intended landing location, he felt the tail oscillate to the right and back and heard increase and decrease in engine speed. About 200 ft agl, he thought he may land short of the intended location, and he made adjustments to the collective and cyclic to maintain rotor RPM and airspeed. The pilot then initiated a flare and landing. After the helicopter came to rest, the flight paramedic mentioned the helicopter was on fire, and the pilot noticed a fire near the No. 2 engine. PERSONNEL INFORMATIONA review of the pilot's records and telephone interviews revealed the pilot was hired by Pentastar in August 2016 and primarily flew the EC135 P2+ helicopter. His most recent Federal Aviation Regulations Part 135 competency check was completed March 31, 2018, in the EC135 P2+ helicopter, which was equipped with a different cockpit display than the EC135 P1 accident helicopter. At the time of the accident, the pilot had accumulated about 319 flight hours in the EC135 P2+, with about 11 total hours in the EC135 P1. The pilot completed the Pentastar "RW EC-135P1 Differences Training", which was an online self-study course, on February 18, 2018. The online course included, but was not limited to, the following differences: Cockpit Display System (CDS) versus Center Panel Display System (CPDS) (P2+), analogue versus first limit indicator (FLI) all engines operative and one engine inoperative limits, and twist grip controls. In addition, the pilot stated he completed some "hands-on" EC135 P1 training with other company pilots, and familiarization flights. The pilot had not received any simulator training for the EC135 P1 helicopter as there was no EC135 P1 simulator available at any worldwide training facility. AIRCRAFT INFORMATIONAccording to Pentastar, the helicopter was maintained according to the manufacturer's inspection program, and the most recent inspection was completed on April 2, 2018. At the time of the accident, the helicopter had accrued 6,555.4 flight hours. The helicopter was not equipped or certified for instrument flight rules operations. The engines were equipped with Electronic Engine Control (EEC). The engine throttles (twist grips) were mounted on the collective. The forward throttle was for the No. 1 (left position) engine, and the aft throttle was for the No. 2 (right position) engine. For the throttles to be in the neutral position, a white line and the letter "N" on each throttle need to be aligned with a white arrow on the collective. There was a detent when the throttle was rolled across the neutral position, which matched the painted positions that were mid-way between the full open and minimum idle positions. Normal flight was conducted with the throttles in the neutral position, allowing the EECs to control the engines. The EECs provided several functions, which included the scheduling of fuel and maintaining engine operation within predetermined limits. The airframe manufacturer refers to the engine EECs as Full Authority Digital Engine Controls (FADECs) in the cockpit indications. The operator's helicopter fleet consisted of two EC135 P2+ helicopters, and one EC135 P1 helicopter. Manual Engine Control According to the EC135 P1 CDS flight manual, if either throttle were rolled out of the neutral position, two annunciator lights would illuminate on the CDS; ENG MANUAL (engine manual) and TWIST GRIP, and a yellow master caution light in the pilot's field of view on the instrument panel. The ENG MANUAL light indicated that the FADEC no longer controlled that engine, and the movements of the collective up or down would not automatically result in engine power changes to maintain constant rotor speed. The TWIST GRIP light indicated that the throttle was not in the neutral position but was unaffected by whether the engine was in manual or under FADEC control. The rotorcraft flight manual (RFM) page 3-16, indicated the following warning about operating the engine in the manual mode: "OPERATE THE TWIST GRIP WITH GREAT CARE AND AVOID QUICK TWIST GRIP ROTATIONS. HOLD MIN. 10% TORQUE ON THE NORMAL ENGINE TO MAINTAIN AUTOMATIC CONTROL OF [Rotor Speed]." The RFM page 3-34, effective after alert service bulletin (ASB) EC135-76A-002 had been completed, also noted that if a throttle were rolled out of the neutral position and if the residual torque on the engine in MANUAL mode was greater than 10%, the respective engine twist grip should be moved to the neutral position. If the residual torque on the engine in MANUAL mode was less than 10%, the respective guarded ENG MODE SEL switch on the overhead panel must be switched to MANUAL then to NORM, followed by verification of ENG MANUAL caution light extinguished, the respective engine twist grip moved to the neutral position, and verification of correct operation in NORM mode through small collective movements. In either case, if the TWIST GRIP caution indication remained on, LAND AS SOON AS PRACTICAL. Once the throttle was returned to the neutral position, the TWIST GRIP light would extinguish; however, if the throttle were rotated from the neutral position again, in either direction, the engine would revert to manual control, and the process would have to be repeated. According to the helicopter manufacturer, with one engine in manual mode, and the other under EEC control, a reduction in power (using the twist grip to reduce fuel flow) on the manual engine would result in a power increase on the engine under EEC control (in an effort to maintain the rotor speed), up to the predetermined limits. If power was increased on the engine in manual mode (using the twist grip), then the power could increase to the engine fuel control limits, and there would be a corresponding decrease in power on the engine under EEC control. AIRPORT INFORMATIONAccording to Pentastar, the helicopter was maintained according to the manufacturer's inspection program, and the most recent inspection was completed on April 2, 2018. At the time of the accident, the helicopter had accrued 6,555.4 flight hours. The helicopter was not equipped or certified for instrument flight rules operations. The engines were equipped with Electronic Engine Control (EEC). The engine throttles (twist grips) were mounted on the collective. The forward throttle was for the No. 1 (left position) engine, and the aft throttle was for the No. 2 (right position) engine. For the throttles to be in the neutral position, a white line and the letter "N" on each throttle need to be aligned with a white arrow on the collective. There was a detent when the throttle was rolled across the neutral position, which matched the painted positions that were mid-way between the full open and minimum idle positions. Normal flight was conducted with the throttles in the neutral position, allowing the EECs to control the engines. The EECs provided several functions, which included the scheduling of fuel and maintaining engine operation within predetermined limits. The airframe manufacturer refers to the engine EECs as Full Authority Digital Engine Controls (FADECs) in the cockpit indications. The operator's helicopter fleet consisted of two EC135 P2+ helicopters, and one EC135 P1 helicopter. Manual Engine Control According to the EC135 P1 CDS flight manual, if either throttle were rolled out of the neutral position, two annunciator lights would illuminate on the CDS; ENG MANUAL (engine manual) and TWIST GRIP, and a yellow master caution light in the pilot's field of view on the instrument panel. The ENG MANUAL light indicated that the FADEC no longer controlled that engine, and the movements of the collective up or down would not automatically result in engine power changes to maintain constant rotor speed. The TWIST GRIP light indicated that the throttle was not in the neutral position but was unaffected by whether the engine was in manual or under FADEC control. The rotorcraft flight manual (RFM) page 3-16, indicated the following warning about operating the engine in the manual mode: "OPERATE THE TWIST GRIP WITH GREAT CARE AND AVOID QUICK TWIST GRIP ROTATIONS. HOLD MIN. 10% TORQUE ON THE NORMAL ENGINE TO MAINTAIN AUTOMATIC CONTROL OF [Rotor Speed]." The RFM page 3-34, effective after alert service bulletin (ASB) EC135-76A-002 had been completed, also noted that if a throttle were rolled out of the neutral position and if the residual torque on the engine in MANUAL mode was greater than 10%, the respective engine twist grip should be moved to the neutral position. If the residual torque on the engine in MANUAL mode was less than 10%, the respective guarded ENG MODE SEL switch on the overhead panel must be switched to MANUAL then to NORM, followed by verification of ENG MANUAL caution light extinguished, the respective engine twist grip moved to the neutral position, and verification of correct operation in NORM mode through small collective movements. In either case, if the TWIST GRIP caution indication remained on, LAND AS SOON AS PRACTICAL. Once the throttle was returned to the neutral position, the TWIST GRIP light would extinguish; however, if the throttle were rotated from the neutral position again, in either direction, the engine would revert to manual control, and the process would have to be repeated. According to the helicopter manufacturer, with one engine in manual mode, and the other under EEC control, a reduction in power (using the twist grip to reduce fuel flow) on the manual engine would result in a power increase on the engine under EEC control (in an effort to maintain the rotor speed), up to the predetermined limits. If power was increased on the engine in manual mode (using the twist grip), then the power could increase to the engine fuel control limits, and there would be a corresponding decrease in power on the engine under EEC control. WRECKAGE AND IMPACT INFORMATIONExamination of the accident site revealed the initial impact was consistent with the tail bumper contacting the terrain, followed by the landing gear skids and fuselage. The left landing gear skid was separated and came to rest near the ground scar that was consistent with the fuselage impact. The fuselage was crushed upward, and the fenestron structure was separated near the tailboom attachment location. The helicopter had rotated 180° from the direction of impact and came to rest upright. Three main rotor blades displayed fractures near the root, and one blade was relatively undamaged. The pilot seat (right front) and paramedic seat (left aft, aft-face) were found fully attenuated. The flight nurse seat (right aft, forward-face) two floor legs were fractured, and the seat back was separated from the aft wall brackets. The ENG 1 twist grip (forward) was in the "Max" position, and the ENG 2 twist grip (aft) was in the near "Max" position. Both engines ENG MOD SEL switches were in the "normal" position, and the switch guard in place. The ENG CONTROL switches were unguarded and in the "off" position. The FADEC switches were in the "on" position. The rotor brake was engaged. Thermal damage was noted on the No. 2 engine and main transmission cowling. Both engines power turbine wheel blades were missing the outer halves of the blades. Multiple impact dents, consistent with the fractured turbine blades, were noted inside the exhaust stubs of both engines. The No. 1 engine had a 1/2" by 1/2" hole in the exhaust stub at the 1 o'clock position forward of the aft firewall, and the No. 2 engine had a 2" by 1" hole in the exhaust stub at the 10 o'clock position forward of the aft firewall. The engines and FADEC components (Electronic Engine Controls (EECs) and Data Collection Units (DCUs)) were removed and shipped to Pratt & Whitney Canada (PWC) for further examination. Control continuity was established from the cyclic and collective controls to the rotor head. Tail rotor control continuity was established from the anti-torque pedals to the breaks in the tailboom, and then from the breaks to the fenestron. The main transmission was intact and secure in its mounts. Continuity was established through the transmission to its accessories. ADDITIONAL INFORMATIONPer Federal Regulation 14 CFR 135.607, helicopters in air ambulance operations must be equipped with an approved flight data monitoring (FDM) system capable of recording flight performance data. This rule w
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 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.
Source: NTSB Aviation Accident Database
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