MBB/Kawasaki BK 117

Origins in Germany 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==

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. An optional Sperry-built three-axis stability augmentation system also served to improve the rotorcraft's ease of handling. ==Accidents and incidents==

A BK 117-B2 helicopter contracted by the New South Wales Rural Fire Service to fight fires crashed on 17 August 2018, the pilot died in the crash. 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==

;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 ; • Fire and Rescue NSW (formerly) • New South Wales Rural Fire Service BK 117 • Western Australia Police ; • Chilean Air Force • Carabineros de Chile ; • Colombian National Armada ; • Prefectural police departments Police BK 117 ; • Malagasy Air Force ; • Peruvian National Police ; • Ministry of Emergency Situations ; • Guardia Civil ; • South African Air Force ; • Riverside County Sheriff's Department (California) Civil 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 ; • Yellowhead Helicopters Ltd. • Shock Trauma Air Rescue Society • Helico Secours • Airmedic • HALO Air Ambulance ; • Everett Aviation ; • Auckland Rescue Helicopter Trust • Life Flight (New Zealand) • Canterbury West Coast Air Rescue Trust • Otago Rescue Helicopter Trust ; • Rega (air rescue) : 7 H145 since 2018, replacing the EC145 ; • Daily Air ; • Si Chang Flying Services ; • Air Methods • St. Louis Children's Hospital • Orlando Regional Medical Center Former ; • Bophuthatswana Air Force ; • Canadian Forces Air Command ; • ADAC • DRF Luftrettung • Bundeswehr • German State Police ; • Transkei Defence Force ; • Venda Defence Force ==Specifications (BK 117 B-2)==