MBB/Kawasaki BK 117

The MBB/Kawasaki BK 117 is a twin-engined light utility–transport helicopter. It was jointly developed and manufactured by Messerschmitt-Bölkow-Blohm (MBB) of West Germany and Kawasaki of Japan. MBB was later purchased by Daimler-Benz and eventually became a part of Eurocopter, which was later rebranded as Airbus Helicopters.

On 25 February 1977, MBB and Kawasaki signed a cooperative agreement to abandon their independent efforts to design twin-engined general purpose helicopters in favor of a collaborative venture to development of a new rotorcraft for that role. While the program's costs were shared equally, the workshare was divided into certain areas of the design. MBB utilized their expertise with the rigid rotor system used on the earlier Bo 105 to develop the majority of the dynamic systems and flight controls, while Kawasaki focused on the airframe, structural elements, and various other components. On 13 June 1979, MBB's flying prototype conducted its maiden flight at Ottobrunn, Bavaria, Germany; months later, it was followed by the Kawasaki prototype at Gifu, Chūbu region, Japan on 10 August 1979.

Each company established their own final assembly line, producing the BK 117 for their respective regions. The BK 117 has proven to be popular for passenger services and VIP-transport; the cabin can be outfitted with various seating configurations, for between seven to ten passengers. It is also used for a diverse range of other operations, such as aerial crane and sling work, law enforcement, and military transport, and is exceptional as an air ambulance and search and rescue platform. Due to its popularity, during the 1990s a refined derivative—initially marketed as the BK 117 C-2, before being rebranded as the EC145 and, yet later, the H145—was developed from the BK 117 C-1 version; this improved version of the rotorcraft has since succeeded the original BK 117 in production.

The original BK 117, Eurocopter EC145, and Airbus Helicopters H145, are typically thought of as being in one design family, despite different marketing and naming.

Development

Origins

thumb|left|Second prototype at [[Hubschraubermuseum Bückeburg in Germany]]

thumb|Third prototype of the BK 117, on display since 2001 in Japan

According to aviation author J. Mac. McCellan, the BK 117 has its origins in an earlier rotorcraft designed and produced by German aerospace manufacturer Messerschmitt-Bölkow-Blohm (MBB), the MBB Bo 105. This helicopter, which proved to be a commercial success, had made use of a revolutionary hingeless main rotor composed of fibreglass, which was developed by German engineer Ludwig Bölkow. Having established a reputation for reliability and safety, during the early 1970s MBB, along with one of its major shareholders, Boeing Vertol, began studying options for producing an enlarged derivative of the type to accompany the Bo 105. However, Boeing soon withdrew from the venture, leading to MBB searching for another partner; this was found in the form of Japanese company Kawasaki Heavy Industries.

On 25 February 1977, MBB and Kawasaki signed an agreement to cooperate on the development of a new rotorcraft. Under the terms of this agreement, the two corporations merged their previously separate projects to produce twin-engined general purpose helicopters, these being the Bo 107 by MBB and the KH-7 from Kawasaki. All of the privately incurred development costs were shared equally between the two partners; in November 1977, the program received a huge boost when the government of West Germany announced that it would fund half of the costs of development. By April 1978, project definition studies had been completed, enabling the joint venture to proceed with the detail design phase of development.

Design

thumb|left|Head on view of BK 117

thumb|Bk 117 B2 cockpit

thumb|Doors open BK 117 P2

The MBB/Kawasaki BK 117 is a twin-engined medium utility–transport helicopter. It possessed several attributes that lend itself to performing many different roles, such as twin-engine redundancy, sizable clamshell-shaped rear-facing double doors, and a relatively spacious cabin; one mission to which it was deemed to be suitable was the emergency medical services (EMS). The airframe is composed of rivetted metal, making minimal use of composite materials. In order to free up internal space, both the engines and transmission are positioned above the main cabin. Considerable efforts were made to reduce the weight of the aircraft without compromising the aircraft's structural integrity. The engines are regulated using a specialized control system which smoothly and evenly regulate RPM and torque between both engines, even during vigorous maneuvers. In terms of its flight performance, the type was considered to be suitable for the execution of various aerobatic maneuvers, such as flying loops and rolls, while retaining such levels of inherent stability that pilots could readily release both the cyclic and collective controls, unlike the majority of rotorcraft.

A BK 117-B2 helicopter operated by Search and Rescue Services Limited crashed into Mount Pirongia on 19 September 2023 after the helicopter rapidly dropped in height, of the 3 people abroad, all survived.

A BK 117-B2 helicopter owned by Air Methods LLC crashed on 24 April 2025 during takeoff near the runway, of the 3 people aboard all survived.

Operational history

A single BK 117 A-3 (c/n 7106) was leased by the Canadian Forces Air Command for a test program and designated as the CH-143. When the program was over, the aircraft was returned to MBB Canada.

Variants

thumb|BK 117 P2 in Police service

thumb|JASDF BK 117 A4

;BK 117 P-2 (D-HBKA):German prototype, first flown 13 June 1979. Now exhibited at the Bückeburg helicopter museum, Bückeburg, Germany.

;BK 117 S-01 (D-HDRF):Initial pre-production prototype. Now preserved on top of the DRF-Headquarters at Stuttgart Airport.

;BK 117 P-3/P-5 (JQ0003):Japanese prototype, first flown 10 August 1979. Now exhibited at Kakamigahara Aerospace Museum, Kakamigahara/Gifu, Japan

;BK 117 A-1 :Powered by two Lycoming LTS 101-650B-1 engines. First flown 23 April 1982.

;BK 117 A-3 :Introduced in March 1985, the A-3 has a larger tail rotor with improved blades, Yaw CSAS, improved stability (SPAS) and the take-off weight increased to 3,200 kg (7,055 lb).- The Canadian Armed forces leased a single BK 117-A3 for a test program and designated it the CH-143. When the program was over, the aircraft was returned to MBB Canada

;BK 117 A-4 :Introduced in July 1986, the A-4 has increased transmission limits at take-off power, improved tail rotor head. German aircraft have provision for extra internal fuel, giving enhanced performance.

;BK 117 A-3M :Military version introduced in 1986. The A-3M is fitted with taller skids and can carry 11 troops. A Browning 12.7 mm (0.5 in) machine gun can be mounted under the fuselage in a Lucas turret with 450 rounds and controlled by a helmet-mounted sight. The A-3M also has outrigger pylons which can hold up to eight HOT II or TOW antitank missiles or a variety of air-to-air missiles, rocket-pods, or forward-firing cannons. Provisions for a doorway gunner's position with a 12.7 mm (0.5 in) gun can also be installed.

;BK 117 B-1 :Introduced in December 1987, the B-1 is fitted with LTS 101-750B-1 engines to provide increased performance, and a 140 kg (309 lb) increase in payload.

;BK 117 B-1C :UK-certified version with reduced range and endurance.

;BK 117 B-2 :Maximum Gross Weight increased to 3,350 kg, 2 x Allied Signal Lycoming LTS101-750B-1 engines fitted as standard, new tail rotor blades, improved "hot and high" performance, take-off/landing limitation increased to 15,000 ft, improved flight performance for: HIGE/HOGE, single engine service ceiling.

;BK 117 C-1 :Powered by two Turbomeca Arriel 1E engines. Later models may be upgraded to Arriel 1E2 engines.

;NBK 117 :License-built model produced in Indonesia by Indonesian Aerospace.

;BK 117-850D2 :Introduced in 2010, the 850D2 variant is an STC (Supplementary Type Certificate) development (i.e., re-engined) of BK 117 B-2 incorporating Honeywell LTS 101-850B-2 engines aimed at improving OEI and Category A performance. Development and certification was conducted in New Zealand by Airwork of Ardmore, NZ, in conjunction with Flight Structures Ltd.

NOTE: All later models are derived from the BK 117 by (initially) Eurocopter Deutschland and (later) Airbus Helicopters. The models BK 117-C2, -D2, and -D3 are therefore better known under their commercial naming convention as the EC145 or H145. Nevertheless, all models share the same EASA Type Certificate (see EASA Type Certificate Data Sheet).

Operators

Military and government

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Fire and Rescue NSW (formerly)
New South Wales Rural Fire Service

thumb|A [[Federal Police (Germany)|Polizei BK 117 ]]

Western Australia Police

;

Chilean Air Force
Carabineros de Chile

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Colombian National Armada

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Prefectural police departmentsthumb|[[Saitama Prefecture|Saitama Prefectural Police BK 117]]

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Malagasy Air Force

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Peruvian National Police

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Ministry of Emergency Situations

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Guardia Civil

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South African Air Force

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Riverside County Sheriff's Department (California)

Civil

thumb|A PolAir 5' BK 117 in flight

thumb|right|[[Shock Trauma Air Rescue Society|STARS Air Ambulance at Foothills Medical Centre in Canada]]

The majority of the helicopters are operated by various emergency services although it is also operated by private individuals, companies and executive charter operators.

;

CareFlight
Westpac Life Saver Rescue Service

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Yellowhead Helicopters Ltd.

Shock Trauma Air Rescue Society
Helico Secours
Airmedic
HALO Air Ambulance

;

thumb|220x220px|Airmedic BK117 B2 in flight

Everett Aviation

;

thumb|BK 117 in service with [[Auckland Rescue Helicopter Trust]]

Auckland Rescue Helicopter Trust
Life Flight (New Zealand)
Canterbury West Coast Air Rescue Trust
Otago Rescue Helicopter Trust

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Rega (air rescue) : 7 H145 since 2018, replacing the EC145

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Daily Air

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Si Chang Flying Services

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Air Methods
St. Louis Children's Hospital
Orlando Regional Medical Center

Former

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Bophuthatswana Air Force

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Canadian Forces Air Command

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ADAC
DRF Luftrettung
Bundeswehr
German State Police

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Transkei Defence Force

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Venda Defence Force

Specifications (BK 117 B-2)

References

Citations

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. .
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. .
Lambert, Mark. Jane's All The World's Aircraft 1993–94. Coulsdon, UK:Jane's Data Division, 1993. .
McCellan, J. Mac. "Paramedic." Flying, February 1986. Vol. 113, No. 2. pp. 62–67. .
Mlandenov, Alexander. "Russia's Responders". Air International, Vol. 91, No. 6, December 2016. pp. 78–87. .
Prétat, Samuel. "EC 145 & UH-72." Éditions Minimonde76, 2015. .
Scharenborg, Martin. "Fighting the fires". Air International, Vol. 103 No. 2, September 2022. pp. 68–72. .

External links

Manufacturer's website
BK 117 in aeromedical services
BK 117 factsheet