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MBB/Kawasaki BK 117

From Alfawiki
Messerschmitt-Bölkow-Blohm (MBB) and Kawasaki Heavy Industries
Company typeJoint venture
IndustryAerospace, Helicopter manufacturing
Founded25 February 1977
Headquarters
Germany, Japan
ProductsBK 117 helicopter

The MBB/Kawasaki BK 117 is a light twin-engine helicopter designed for utility and transport purposes, developed through a collaboration between Messerschmitt-Bölkow-Blohm (MBB) of Germany and Kawasaki Heavy Industries of Japan. Following MBB’s acquisition by Daimler-Benz, the company became part of Eurocopter, which is currently known as Airbus Helicopters.

On 25 February 1977, MBB and Kawasaki consolidated their individual twin-engine helicopter projects into a unified development effort. Both parties shared the development expenses equally, with MBB taking charge of dynamic systems and flight control mechanisms, drawing on its expertise from the rigid rotor technology of the MBB Bo 105, while Kawasaki was responsible for the airframe and structural elements. The MBB prototype conducted its maiden flight on 13 June 1979 in Germany, followed by Kawasaki’s prototype flying on 10 August 1979 in Japan.

Each manufacturer maintained separate assembly facilities to produce the BK 117 tailored to their respective regional markets. The helicopter gained popularity in passenger and VIP transport sectors due to its adaptable cabin layout accommodating seven to ten occupants. It also fulfills a wide range of functions such as aerial crane operations, law enforcement, military transport, medical evacuation, and search and rescue tasks.

During the 1990s, the BK 117 C-1 was upgraded to the BK 117 C-2, which was subsequently marketed as the Eurocopter EC 145 and is now known as the H145. This model replaced the original BK 117 in production.

Although bearing different designations, the initial BK 117, Eurocopter EC 145, and Airbus Helicopters H145 are recognized as members of one continuous design lineage.

Origins

The BK 117 traces its lineage back to the earlier rotorcraft developed by German aerospace firm Messerschmitt-Bölkow-Blohm (MBB), specifically the MBB Bo 105. This helicopter was notable for introducing an innovative fiberglass hinge-less main rotor system engineered by Ludwig Bölkow. Capitalizing on the Bo 105’s reputation for dependability, MBB and Boeing Vertol explored a larger variant during the early 1970s. After Boeing withdrew from the project, MBB partnered with Japan’s Kawasaki Heavy Industries.

On 25 February 1977, MBB and Kawasaki formalized a joint development agreement combining their separate twin-engine helicopter designs: MBB’s Bo 107 and Kawasaki’s KH-7. The development costs were split evenly, with half of the funding provided by West Germany’s government starting November 1977. By April 1978, preliminary project studies had been finalized, enabling detailed design work to commence.

The division of responsibilities assigned MBB to develop rotors based on the Bo 105’s rigid system, along with the tailboom, flight controls, and hydraulic systems. Kawasaki took charge of landing gear design, airframe construction, main transmission components, electrical systems, and various smaller parts. BMW contributed consulting services related to styling. Both companies set up independent final assembly lines dedicated to their respective domestic markets.

Initially planned to build two prototypes each, Kawasaki ultimately produced only one. The first prototype built by MBB flew on 13 June 1979 in Ottobrunn, Germany; Kawasaki’s prototype followed with its maiden flight on 10 August 1979 in Gifu, Japan. Development progressed more slowly than anticipated due to shortages of skilled labor at MBB. Certification processes extended beyond the originally targeted end of 1980: German certification was granted on 9 December 1982, Japanese certification on 17 December 1982, and US Federal Aviation Administration approval was obtained on 29 March 1983, facilitating entry into global markets.

Continued Evolution

The first production variant, known as the BK 117A-1, entered service in 1983. It was soon followed by newer versions: the BK 117A-3 introduced in 1985 featured a higher maximum takeoff weight and an enlarged tail rotor with twisted blades; the BK 117A-4 released in 1987 incorporated LTS 101-750B-1 engines to improve performance under hot and high conditions, upgraded the main rotor transmission, enhanced the tail rotor mast, and included a larger fuel capacity. In 1990, MBB’s U.S. subsidiary launched a corporate edition equipped with a Honeywell SPZ-7000 digital automatic flight control system and a cocoon-style interior design; optional equipment comprised Bendix/King EFIS and clamshell cabin doors. The BK 117C-1 model of 1992 featured an updated EFIS panel, improved environmental control systems, and additional enhancements for hot-and-high operations.

At the 1985 Paris Air Show, a military adaptation called the BK 117A-3M was revealed. This attack helicopter variant was designed to carry eight Euromissile HOT 2 missiles along with a chin-mounted turret built by Lucas housing a Browning 12.7mm machine gun, which was controlled via a helmet-mounted sight. It also incorporated advanced targeting technologies such as an SFIM APX-M 397 stabilized sight mounted on the roof and required elevated skid landing gear to provide clearance for the turret.

Throughout the 1990s, building upon its commercial achievements, the BK 117 C-2—later renamed Eurocopter EC 145 and eventually H145—was developed as an evolution of the BK 117 C-1. This updated model replaced earlier BK 117 versions in production lines. In total, 443 BK 117 helicopters were manufactured: MBB produced 329 units plus two prototypes at Donauworth, while Kawasaki completed 111 units plus one prototype in Japan. A licensing agreement allowed Indonesian Aerospace to produce the helicopter as the NBK 117 domestically; however, this program ceased after only a few aircraft were completed.

Following production cessation, aftermarket upgrade programs emerged from third-party providers. Notably, in 2010 Airwork introduced an engine retrofit replacing the original LTS101-750B-1 turboshafts with more powerful LTS101-850B-2 models, resulting in improved performance, reliability, and safety; this conversion was designated the BK117-850D2. By 2016, nearly fifty helicopters had undergone this upgrade.

Technical Overview

The MBB/Kawasaki BK 117 is a twin-engine medium utility and transport helicopter engineered for multiple mission profiles, including emergency medical services (EMS). Its design highlights include twin-engine redundancy for safety, large rear clamshell doors facilitating access, and a roomy cabin adaptable to diverse operational requirements. The airframe is primarily constructed from riveted metal components with limited composite use to maximize internal volume; engines and transmission systems are positioned above the cabin roofline. Weight optimization was a priority without sacrificing structural strength.

Early variants of the BK 117 utilized two Lycoming LTS101 turboshaft engines, each delivering approximately 550 shaft horsepower at takeoff with sufficient reserve power for continued single-engine flight. These engines were calibrated to operate at lower-than-standard RPMs to boost reliability and extend service life. A dedicated control system maintained balanced RPM and torque distribution between both engines during flight maneuvers. An automatic engine governor simplified power adjustments by allowing pilots to concentrate on monitoring torque output and temperature parameters. The helicopter is certified for instrument flight rules (IFR) operations and supports single-pilot control.

According to aviation publication Flying, the BK 117’s rigid four-bladed main rotor system provides exceptional stability and maneuverability, enabling steeper approach angles compared to competing models. The rotor’s smaller diameter and slower rotational speed reduce vibration levels and noise emissions while permitting operation from confined landing zones. The tail boom is mounted high with an elevated tail rotor to enhance ground safety margins. The aircraft’s performance envelope includes aerobatic capabilities such as loops and rolls while maintaining sufficient stability for pilots to release cyclic and collective controls—a rare characteristic among helicopters. Additionally, an optional Sperry three-axis stability augmentation system further improves handling ease and pilot workload reduction.

Operational History

One BK 117 A-3 (construction number 7106) was temporarily leased by the Canadian Forces Air Command for evaluation purposes and was designated as the CH-143. Upon completion of the trial, the helicopter was returned to MBB Canada.

On 17 August 2018, a BK 117 operated by the New South Wales Rural Fire Service was involved in a crash during firefighting activities, which tragically resulted in the pilot's fatality.

Variants

BK 117 P-2 (D-HBKA)
German prototype that first flew on 13 June 1979. This aircraft is displayed at the Bückeburg helicopter museum in Germany.
BK 117 S-01 (D-HDRF)
The initial pre-production prototype, now preserved on display atop the DRF Headquarters at Stuttgart Airport.
BK 117 P-3/P-5 (JQ0003)
Japanese prototype with a maiden flight on 10 August 1979, currently exhibited at the Kakamigahara Aerospace Museum in Japan.
BK 117 A-1
Equipped with two Lycoming LTS 101-650B-1 engines; its first flight occurred on 23 April 1982.
BK 117 A-3
Released in March 1985, featuring a larger tail rotor, Yaw Control Stability Augmentation System (CSAS), enhanced stability through SPAS, and an increased maximum takeoff weight of 3,200 kg. The Canadian Armed Forces leased one unit for testing under the designation CH-143.
BK 117 A-4
Introduced in July 1986 with upgraded transmission limits and an improved tail rotor head. German variants include additional internal fuel tanks to boost operational range.
BK 117 A-3M
Military adaptation launched in 1986, incorporating taller landing skids, capacity for up to eleven personnel, and options for armament such as a Browning 12.7 mm machine gun and missile mounting points.
BK 117 B-1
Debuted in December 1987 with upgraded LTS 101-750B-1 engines enhancing performance and allowing a payload increase of approximately 140 kg.
BK 117 B-1C
UK-certified model characterized by reduced operational range and endurance.
BK 117 B-2
Features an increased maximum gross weight of 3,350 kg, powered by Allied Signal Lycoming LTS101-750B-1 engines, new tail rotor blades, improved capabilities for "hot and high" conditions, and overall enhanced flight performance.
BK 117 C-1
Powered by twin Turbomeca Arriel 1E engines with later versions upgradable to Arriel 1E2 models.
NBK 117
Indonesian license-produced variant manufactured by Indonesian Aerospace.
BK 117-850D2
Launched in 2010 as a Supplemental Type Certificate (STC) upgrade of the BK 117 B-2, equipped with Honeywell LTS101-850B-2 engines to improve One Engine Inoperative (OEI) and Category A performance. This development and certification process took place in New Zealand through Airwork and Flight Structures Ltd.

NOTE: Subsequent models evolved from the BK 117 by Eurocopter Deutschland and Airbus Helicopters—specifically BK 117-C2, -D2, and -D3—are marketed as the EC145 and H145. These variants all share the same EASA Type Certificate.

Military and Government

Civil

The BK 117 helicopter is extensively employed by emergency response organizations around the globe. Additionally, it serves private owners, business enterprises, and providers of executive charter flights.

  • Everett Aviation
  • Since 2018, Rega (air rescue) has operated seven H145 helicopters, which have replaced their EC145 fleet.
  • Daily Air Corporation
  • Si Chang Flying Services

Former

  • ADAC – modernized its helicopter fleet with Eurocopter EC145 T2 and EC135 models
  • DRF Luftrettung
  • Bundeswehr
  • German State Police

Bibliography

  • "BK 117...a Terrestrial Space Ship". Air International, Vol 36 No 4, April 1989. Bromley, UK: Fine Scroll. . pp. 163–170.
  • Eriksson, Sören. "Clusters and Economic Growth in Asia." Edward Elgar Publishing, 2013. ISBN 0-85793-009-5.
  • Hatch, Paul. "World's Air Forces". Flight International, 5–11 December 1990. pp. 35–81.
  • Hoyle, Craig. "World Air Forces Directory". Flight International, Vol. 182, No. 5370, 11–17 December 2012. pp. 40–64. Template:ISSN.
  • Lambert, Mark. Jane's All The World's Aircraft 1993–94. Coulsdon, UK:Jane's Data Division, 1993. ISBN 0-7106-1066-1.
  • McCellan, J. Mac. "Paramedic." Flying, February 1986. Vol. 113, No. 2. pp. 62–67. Template:ISSN.
  • Mlandenov, Alexander. "Russia's Responders". Air International, Vol. 91, No. 6, December 2016. pp. 78–87. Template:ISSN.
  • Prétat, Samuel. "EC 145 & UH-72." Éditions Minimonde76, 2015. ISBN 9-782954-18181-3. (in French)
  • Scharenborg, Martin. "Fighting the fires". Air International, Vol. 103 No. 2, September 2022. pp. 68–72. .

External links

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