Perryville, MO, USA
N238BK
Airbus Helicopters Deutschland MBB-BK 117 B-2
The airline transport pilot was operating an emergency medical services flight. He reported that, about 17 minutes after takeoff while in cruise flight at dusk, the helicopter "experienced a sharp change in attitude yawing to the left with a hard-upward bump," followed by a change in engine noise. He saw that the engine gas generator speed (N1) gauges for each engine were indicating below 40% and decreasing and that the No. 1 engine low warning light, the No. 1 generator light, and the battery discharge warning lights were illuminated. The pilot stated that the helicopter suddenly "pitched nose up and rolled to the right" and that he then heard the rotor speed begin to deteriorate. He entered an autorotation by applying right forward cyclic and lowering the collective to full down. During the autorotative descent, he saw power lines and a ditch, which required him to change the helicopter's flightpath and land on the far side of the ditch. He flared the helicopter about 100 ft above ground level, and the rotor speed began to decay rapidly. He stated that he attempted to level the helicopter "as it began to fall," but the helicopter landed right skid low and then skidded for about 100 ft. The main rotor blades hit the ground as the helicopter rolled onto its right side. The pilot reported that, after exiting the helicopter, he observed fuel draining in a solid stream from a fuel vent port on the helicopter's belly and that he then re-entered the cockpit and turned off all electrical and fuel switches to minimize the risk of fire. The pilot's recollection of the accident circumstances was consistent with a dual-engine loss of power. Additionally, the damage observed on the rotor system was consistent with the engine not having power at the time of impact. The fuel transfer system between the main tanks and the supply tanks and from the supply tanks to their respective engines and the fuel delivery system functioned normally during operational testing. No residual fuel was found within the engine fuel filter bowl, indicative of no fuel reaching the engines. Based on the pilot's statement that he saw a steady stream of fuel leaking from a fuel vent port on the helicopter's belly shortly after the accident, fuel was likely present within the main fuel tanks. Therefore, based on the evidence, it is likely that the pilot did not activate the fuel transfer pumps, which resulted in no fuel transferring between the main fuel tanks and the supply tanks and led to eventual fuel starvation. Thus, when the engines consumed all available fuel from their respective supply tanks, the dual-engine loss of power occurred. The advisory, caution, and warning annunciator panel functioned normally during operational testing. However, postaccident examination of the helicopter revealed that the dimming function was activated, and the pilot confirmed that he dimmed the panel before takeoff. The annunciator panel contains caution lights for when the fuel transfer pumps are off and for when the fuel quantity in each supply tank is low. Illumination of these caution lights leads to the illumination of the master warning light but generates no aural tones. The ambient light at the time of the flight and the pilot's activation of the dimming function in conjunction with the night vision imaging system filters likely precluded the pilot from being able to see the illuminated caution lights on the annunciator panel and an illuminated master warning light.
HISTORY OF FLIGHTOn July 1, 2017, about 2036 central daylight time, an Airbus Helicopters Deutschland, MBB-BK 117 B-2, N238BK, helicopter, landed hard and rolled over during an emergency landing to a field near Perryville, Missouri. The pilot, three crew members, and a passenger received minor injuries, and the helicopter sustained substantial damage. The helicopter was owned and operated by Air Methods Corporation, doing business as Kids Flight, as a 14 Code of Federal Regulations Part 135 medical flight. Visual meteorological conditions (dusk) prevailed at the time of the accident, and a company visual flight rules flight plan was filed. The flight originated from the St. Francis Medical Center (MO50), Cape Girardeau, Missouri, about 2019 and was en route to the St. Louis Children's Hospital (2MU1), St. Louis, Missouri. The pilot reported that at 1901, he was notified by the Air Methods Communication Center (AirCom) concerning a flight request. The pilot accepted the flight and after ensuring all necessary requirements were completed, the flight departed at 1922 for MO50, which was approximately 50 nautical miles (nm) to the southeast. The pilot reported that the helicopter departed with 140 gallons of fuel in the main fuel tanks. The flight arrived at MO50 about 1949. About 2015, the medical crew arrived at the helicopter pad and loaded the patient on board the helicopter. About 2019, the helicopter departed for 2MU1, which was approximately 85 nm on a 338° heading. Sunset was about 2025 with the sun setting on a 300° azimuth. The pilot reported that there was 110 gallons in the main fuel tanks. The pilot reported that after 15 minutes of flight, he scanned the instruments and gauges "noting that all systems were in the normal range and fuel was transferring from the main tank." He reported that the fuel level indication was approximately 95 gallons in the main tanks and the supply tanks were "just below the full indication," and that there were no illuminated lights on the warning/caution panel. The airspeed was 120 kts at an altitude of 1,600 ft above mean sea level - about 1,200 ft above ground level (agl). The pilot reported that when the flight was about 5 miles north of Perryville, Missouri, the helicopter "experienced a sharp change in attitude yawing to the left with a hard-upward bump," followed by a change in the engine noise. He observed the N1 gauges both indicating below 40 per cent and decreasing. The No. 1 engine low warning light, the No. 1 generator light, and the battery discharge warning lights were illuminated. He stated, "Suddenly the aircraft pitched nose up and rolled to the right. I could hear the rotor begin to deteriorate." He entered an autorotation by applying right forward cyclic and lowering the collective to full down. During the autorotative descent, he saw power lines and a ditch which required him to change his flight path to land on the far side of the ditch. He flared the helicopter about 100 ft agl and the rotor rpm began to decay rapidly. He attempted to level the helicopter "as it began to fall through." The helicopter landed right skid low and the helicopter skidded for about 100 ft. The main rotor blades hit the ground as the helicopter rolled onto its right side. Once the helicopter came to a rest, he pulled the power levers to the stop position. The pilot and flight crew, with the patient on a stretcher, egressed the helicopter. The pilot reported that he observed fuel draining in a solid stream from one of the drains on the belly of the helicopter. He re-entered the cockpit and turned off all electrical and fuel switches to minimize the risk of fire. PERSONNEL INFORMATIONThe pilot, age 59, held an Federal Aviation Administration (FAA) airline transport pilot certificate with a rotorcraft helicopter, and instrument helicopter ratings. The pilot's most recent FAA second-class medical certificate was dated February 21, 2017, with a restriction for corrective lenses. He had 6,237 hours of total flight time with 308 hours of flight time in the make and model of the accident helicopter. AIRCRAFT INFORMATIONThe Airbus Helicopters Deutschland MBB-BK 117 B-2 helicopter has a four-bladed rigid main rotor system that provides helicopter lift and thrust. A two-bladed tail rotor system provides anti- torque and directional control. The helicopter flight controls are hydraulically assisted by a dual hydraulic system. The helicopter was equipped with a skid-type landing gear and two Honeywell LTS101-750B-1 turboshaft engine. The BK117 B-2 helicopter is type certificated under FAA Type Certificate Data Sheet (TCDS) No. H13EU as a Transport Category A & B helicopter. The accident helicopter, serial number (S/N) 7238, was manufactured in 1991. According to helicopter records, the airframe had accumulated an aircraft total time (ATT) of about 12,150 flight hours the day prior to the accident. The engines installed on the accident helicopter were S/Ns LE45662 AEF and LE45681 EFA, positioned as the No. 1 (left) and No. 2 (right) engines, respectively. The No. 1 engine had accumulated about 9,799.53 hours, about 27,502.20 generator cycles, and about 22,451.90 power turbine cycles around the time of the accident. The No. 2 engine had accumulated about 10,193.60 hours, 27,278.27 gas generator cycles, and 20,832.55 power turbine cycles. A night vision goggle (NVG) compatible interior lighting system, manufactured by Ahlers Aerospace, Inc., was installed under FAA Supplemental Type Certificate (STC) No. SR09523RC. The night vision imaging system (NVIS) kit uses infrared filters that are installed externally to the faces of instruments and displays to reduce or eliminate infrared glare. An infrared filter is also placed over the advisory, caution, and warning annunciator panel. STC No. SR09523RC does not affect the instrument lighting controls originally installed on the helicopter. Helicopter Fuel System Description The helicopter fuel system comprises the fuel storage system, fuel supply system, and fuel monitoring system. The fuel storage system consists of the fuel tanks, tank vent system, tank drain valves, and filler neck. The fuel supply system consists of the fuel tank pumps, fuel lines, and emergency fuel shutoff valves. The fuel monitoring system consists of the fuel quantity indicator, low fuel warning, fuel pressure waning, and fuel filter contamination warning. The helicopter contains four flexible fuel tank bladders: an 80 kg fuel tank, forward main tank, left and right prime (supply) tank, and a rear main tank. The 80 kg fuel tank is connected to the forward main tank via one interconnecting tube. The forward main tank is connected to each supply tank via overflow tubes. The left and right supply tanks are separated but glued together. The left supply tank supplies fuel to the No. 1 engine and the right supply tank supplies fuel to the No. 2 engine. The rear main tank carries the fuel filler neck and is connected to the forward main tank via two upper and one lower interconnecting tubes. The total usable fuel capacity of all fuel tanks is about 184.2 gallons. The 80 kg fuel tank holds about 26.3 gallons, the forward and aft main fuel tanks combined holds about 132.4 gallons, and both supply tanks combined holds about 25.5 gallons. There are four fuel pumps within the helicopter fuel system: two fuel prime pumps and two fuel transfer pumps. Each supply tank contains a prime pump that delivers fuel to the engines via feed lines during engine start. The prime pumps are identified "left" and "right" based on the supply tank in which they reside. The prime pumps are activated using a toggle switch on the center console of the helicopter. Activation of the prime pumps illuminates the "PRIME PUMPS" caution light on the advisory, caution, and warning annunciator panel in the cockpit. Once the engines are running, the engine-driven fuel pumps draw fuel from the supply tanks and the prime pumps can be turned off. Deactivation of the prime pumps extinguishes the "PRIME PUMPS" caution light. The two fuel transfer pumps are identified "forward" and "aft". Both fuel transfer pumps are located within the forward main tank. The transfer pumps deliver fuel from the main fuel tanks to the supply tanks and must be activated during helicopter operation. The capacity of the transfer pumps allows for more fuel to be transferred into the supply tanks than the engines can consume. Any surplus fuel in the supply tanks return to the main fuel tanks via overflow tubes. When the transfer pumps are deactivated, the "F PUMP XFER FWD" and "F PUMP XFER AFT" caution lights illuminate on the annunciator panel. Activation of the respective transfer pumps extinguishes the associated caution lights. Each supply tank contains a fuel quantity transmitter. Additionally, fuel quantity transmitters are installed in the forward main tank and the 80 kg fuel tank. The fuel quantity indicator (gauge) in the cockpit shows three values in gallons: the main fuel tank quantity, the left supply tank fuel quantity, and right supply tank fuel quantity. Each supply tank contains a low fuel warning transmitter that detects when its respective supply tank contains less than 7.6 gallons of fuel. Activation of the low fuel warning transmitter results in illumination of the "FUEL LOW I" or "FUEL LOW II" caution light on the annunciator panel for the left supply tank and right supply tank, respectively. METEOROLOGICAL INFORMATIONAt 1955, the surface weather observation at Hunter Field (SAR), Sparta, Illinois, located 15 nm northeast of the accident site, was: wind light and variable; 10 miles visibility; sky clear; temperature 26° C; dew point 17° C; altimeter 30.05 inches of mercury. AIRPORT INFORMATIONThe Airbus Helicopters Deutschland MBB-BK 117 B-2 helicopter has a four-bladed rigid main rotor system that provides helicopter lift and thrust. A two-bladed tail rotor system provides anti- torque and directional control. The helicopter flight controls are hydraulically assisted by a dual hydraulic system. The helicopter was equipped with a skid-type landing gear and two Honeywell LTS101-750B-1 turboshaft engine. The BK117 B-2 helicopter is type certificated under FAA Type Certificate Data Sheet (TCDS) No. H13EU as a Transport Category A & B helicopter. The accident helicopter, serial number (S/N) 7238, was manufactured in 1991. According to helicopter records, the airframe had accumulated an aircraft total time (ATT) of about 12,150 flight hours the day prior to the accident. The engines installed on the accident helicopter were S/Ns LE45662 AEF and LE45681 EFA, positioned as the No. 1 (left) and No. 2 (right) engines, respectively. The No. 1 engine had accumulated about 9,799.53 hours, about 27,502.20 generator cycles, and about 22,451.90 power turbine cycles around the time of the accident. The No. 2 engine had accumulated about 10,193.60 hours, 27,278.27 gas generator cycles, and 20,832.55 power turbine cycles. A night vision goggle (NVG) compatible interior lighting system, manufactured by Ahlers Aerospace, Inc., was installed under FAA Supplemental Type Certificate (STC) No. SR09523RC. The night vision imaging system (NVIS) kit uses infrared filters that are installed externally to the faces of instruments and displays to reduce or eliminate infrared glare. An infrared filter is also placed over the advisory, caution, and warning annunciator panel. STC No. SR09523RC does not affect the instrument lighting controls originally installed on the helicopter. Helicopter Fuel System Description The helicopter fuel system comprises the fuel storage system, fuel supply system, and fuel monitoring system. The fuel storage system consists of the fuel tanks, tank vent system, tank drain valves, and filler neck. The fuel supply system consists of the fuel tank pumps, fuel lines, and emergency fuel shutoff valves. The fuel monitoring system consists of the fuel quantity indicator, low fuel warning, fuel pressure waning, and fuel filter contamination warning. The helicopter contains four flexible fuel tank bladders: an 80 kg fuel tank, forward main tank, left and right prime (supply) tank, and a rear main tank. The 80 kg fuel tank is connected to the forward main tank via one interconnecting tube. The forward main tank is connected to each supply tank via overflow tubes. The left and right supply tanks are separated but glued together. The left supply tank supplies fuel to the No. 1 engine and the right supply tank supplies fuel to the No. 2 engine. The rear main tank carries the fuel filler neck and is connected to the forward main tank via two upper and one lower interconnecting tubes. The total usable fuel capacity of all fuel tanks is about 184.2 gallons. The 80 kg fuel tank holds about 26.3 gallons, the forward and aft main fuel tanks combined holds about 132.4 gallons, and both supply tanks combined holds about 25.5 gallons. There are four fuel pumps within the helicopter fuel system: two fuel prime pumps and two fuel transfer pumps. Each supply tank contains a prime pump that delivers fuel to the engines via feed lines during engine start. The prime pumps are identified "left" and "right" based on the supply tank in which they reside. The prime pumps are activated using a toggle switch on the center console of the helicopter. Activation of the prime pumps illuminates the "PRIME PUMPS" caution light on the advisory, caution, and warning annunciator panel in the cockpit. Once the engines are running, the engine-driven fuel pumps draw fuel from the supply tanks and the prime pumps can be turned off. Deactivation of the prime pumps extinguishes the "PRIME PUMPS" caution light. The two fuel transfer pumps are identified "forward" and "aft". Both fuel transfer pumps are located within the forward main tank. The transfer pumps deliver fuel from the main fuel tanks to the supply tanks and must be activated during helicopter operation. The capacity of the transfer pumps allows for more fuel to be transferred into the supply tanks than the engines can consume. Any surplus fuel in the supply tanks return to the main fuel tanks via overflow tubes. When the transfer pumps are deactivated, the "F PUMP XFER FWD" and "F PUMP XFER AFT" caution lights illuminate on the annunciator panel. Activation of the respective transfer pumps extinguishes the associated caution lights. Each supply tank contains a fuel quantity transmitter. Additionally, fuel quantity transmitters are installed in the forward main tank and the 80 kg fuel tank. The fuel quantity indicator (gauge) in the cockpit shows three values in gallons: the main fuel tank quantity, the left supply tank fuel quantity, and right supply tank fuel quantity. Each supply tank contains a low fuel warning transmitter that detects when its respective supply tank contains less than 7.6 gallons of fuel. Activation of the low fuel warning transmitter results in illumination of the "FUEL LOW I" or "FUEL LOW II" caution light on the annunciator panel for the left supply tank and right supply tank, respectively. WRECKAGE AND IMPACT INFORMATIONThe helicopter's main fuselage was found resting on its right side in a farm field. The surrounding vegetation was relatively low, and the terrain was relatively flat. The right skid had fractured and partially separated from the main fuselage. The left skid tube appeared relatively intact. Dirt was visible on the underside of the main fuselage. The aft-right loading door was opened, and the aft-left loading door remained closed. The front-left chin bubble was fractured and the wire strike protection cutter on the helicopter chin was partially separated from the fuselage. The tail boom and empennage had separated from the main fuselage but were located immediately adjacent to the main fuselage. The tail boom and empennage came to rest inverted. The tail rotor and tail rotor gearbox remained attached to the vertical fin. One of the two tail rotor blades exhibited a broomstrawed appearance and the other appeared relatively intact. Three of the four main rotor blades appeared to be underneath the main fuselage with their tip ends generally pointed in the aft direction. The fourth main rotor blade tip end was generally pointed to the 4 o'clock direction. T
Fuel starvation due to the pilot’s failure to turn on the fuel transfer pump switches during takeoff, which led to a total loss of engine power. Contributing to the accident was the pilot's improper decision to activate the annunciator panel’s dimming function during dusk, which prevented him from seeing the illuminated fuel transfer pump caution light indicating that the pumps were off and the illuminated caution lights for low fuel in the supply tanks.
Source: NTSB Aviation Accident Database
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