| BK 117 | |
|---|---|
 A BK 117 of theGerman police | |
| General information | |
| Type | Utility / Transport |
| National origin | Germany /Japan |
| Manufacturer | Messerschmitt-Bölkow-Blohm (MBB)/Kawasaki Heavy Industries |
| Status | In production |
| Primary users | DRF |
| History | |
| Manufactured | 1979–present |
| Introduction date | 9 December 1982 |
| First flight | 13 June 1979 |
| Developed into | Eurocopter EC145 |
TheMBB/Kawasaki BK 117 is a twin-engined lightutility–transport helicopter. It was jointly developed and manufactured byMesserschmitt-Bölkow-Blohm (MBB) ofGermany andKawasaki ofJapan. MBB was later purchased byDaimler-Benz and eventually became a part ofEurocopter, which was later rebranded asAirbus 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 earlierBo 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 itsmaiden flight atOttobrunn,Bavaria, Germany; months later, it was followed by the Kawasaki prototype atGifu,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 asaerial crane and sling work,law enforcement, andmilitary transport, and is exceptional as anair ambulance andsearch and rescue platform. Due to its popularity, during the 1990s a refined derivative—initially marketed as theBK 117 C-2, before being rebranded as theEC145 and, yet later, theH145—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.
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According to aviation author J. Mac. McCellan, the BK 117 has its origins in an earlier rotorcraft designed and produced byGerman aerospace manufacturerMesserschmitt-Bölkow-Blohm (MBB), theMBB Bo 105.[1] This helicopter, which proved to be a commercial success, had made use of a revolutionaryhingeless main rotor composed offibreglass, which was developed by German engineerLudwig Bölkow. Having established a reputation for reliability and safety, during the early 1970s MBB, along with one of its majorshareholders,Boeing Vertol, began studying options for producing an enlarged derivative of the type to accompany the Bo 105.[2] However, Boeing soon withdrew from the venture, leading to MBB searching for another partner; this was found in the form ofJapanese companyKawasaki Heavy Industries.[3]
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 theBo 107 by MBB and theKH-7 from Kawasaki.[4] 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 ofWest Germany announced that it would fund half of the costs of development.[5] By April 1978, project definition studies had been completed, enabling the joint venture to proceed with the detail design phase of development.[5]
Separate elements of the design were assigned to each company; MBB were responsible for developing therotors (these were based on the rigid rotor system previously used on MBB'sBo 105), tail boom,flight controls andhydraulic system while Kawasaki undertook the development of thelanding gear,airframe, main transmission, electrical system and other minor components.[3] Germanvehicle manufacturerBMW acted as a consultant on the styling of the BK 117.[5] As per their agreement, each company established their own final assembly line for the type, on which they would produce the rotorcraft to meet demands within their respective local markets.[6][3]
Originally, each company intended to construct a pair ofprototypes (in actuality, Kawasaki opted to only build a single prototype) which were to be completed by 1979; one for flight testing purposes and the others for tie down testing and static testing. On 13 June 1979, MBB's flying prototype conducted itsmaiden flight atOttobrunn,Bavaria, Germany; months later, it was followed by the Kawasaki prototype atGifu,Chūbu region, Japan on 10 August 1979.[6][5] The pace of development on the program had been slower than expected, a problem that was exacerbated by a shortage of skilled manpower that was available at MBB. Although it was originally planned for the rotorcraft'sairworthiness certification to be achieved before the end of 1980, German certification was not achieved until 9 December 1982, being quickly followed by the receipt of Japanese certification on 17 December 1982. On 29 March 1983, the type secured the all-importantUnited StatesFederal Aviation Administration (FAA) certification, clearing it for widespread use.[7][5]
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During 1983, the initial production version, designated as theBK 117A-1 was first delivered.[5] Improved variants were quickly developed; in early 1985, theBK 117A-3, featuring an increased maximum takeoff weight and an enlarged tail rotor with twisted airfoils, was certified; two years later, theBK 117A-4, equipped with LTS 101-750B-1 engines for improved hot/high performance and increased maximum takeoff weight, along with improvements to the main rotor transmission and tail rotor mast, as well as a larger capacity fuel tank, was introduced.[5] During 1990, MBB's American division launched a dedicated corporate version of the BK 117; it was furnished with aHoneywell-built SPZ-7000 digital automaticflight control system and a cocoon-type interior system; optional extras included a Bendix/Kingelectronic flight instrumentation system (EFIS) and a clamshell cabin door. During 1992, theBK 117C-1, equipped with a revised EFIS panel and an improved environmental control system, along with greater hot-and-high performance, was introduced to service.[5]
At one stage, there was considerable attention paid to the concept of a dedicated militarized variant of the type.[5] During the 1985Paris Air Show, the concept of an armedattack helicopter derivative, referred to as theBK 117A-3M, was revealed to the general public. As promoted, this variant would have been capable of being armed with launchers for eightEuromissileHOT 2 missiles and a chin-mountedLucas-builtturret for a Browning 12.7mmmachine gun, aimed using ahelmet-mounted sight.[5] It was also to be equipped with various advanced targeting sensors, including an SFIM APX-M 397 roof-mounted stabilizedsight. In order to provide sufficient ground clearance for the gun turret, the use of higher skid landing gear would have also been necessitated.[5]
During the 1990s, as a result of the commercial success of the type, a refined derivative, initially marketed as theBK 117 C-2 prior to its rebranding as theEC 145 and later as theH145, was developed from the BK 117 C-1 version; this improved version of the rotorcraft has succeeded and eventually replaced the original BK 117 in production. In total, 443 BK 117s were manufactured by the two partners; 329 (and two prototypes) were produced by MBB at their Donauworth facility while 111 (and one prototype) were completed by Kawasaki in Japan. During the 1980s, an agreement was formed withIndonesian Aerospace, enabling the type to beproduced under license inIndonesia, which was accordingly designated as theNBK 117; however, according to economics author Sören Eriksson, the Indonesian production program was terminated after only a handful of rotorcraft were completed.[8][5]
Since exiting production, third parties have produced their own upgrade program for existing BK 117s. In 2010, Airwork launched its conversion program for the type, replacing the original LTS101-750B-1 engine with the newer LTS101-850B-2 engine, increasing both its performance, reliability and safety margins, resulting in theBK117-850D2; by 2016, Airwork had upgraded nearly 50 rotorcraft in this manner.[9]
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The MBB/Kawasaki BK 117 is a twin-engined mediumutility–transport helicopter. It possessed several attributes that lend itself to performing many different roles, such as twin-engine redundancy, sizableclamshell-shaped rear-facing double doors, and a relatively spacious cabin; one mission to which it was deemed to be suitable was theemergency medical services (EMS).[10] The airframe is composed ofrivetted metal, making minimal use ofcomposite 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.[3] The cabin could be configured with various interiors in order to suit its purpose.[11]
Early versions of the BK 117 were powered by a pair ofLycoming LTS101turboshaft engines, rated to generate 550 shp at takeoff with considerable reserve power to guard against a single engine failure.[3] While each engine possesses sufficient power to maintain flight and even takeoff in the event of a single engine being rendered inoperable, the type also has favorableautorotation capabilities. In order to extend their operational lifespan and increase their reliability, MBB tuned the engines to operate at lower-than-standardrevolutions per minute (RPM).[11] The engines are regulated using a specialized control system which smoothly and evenly regulate RPM andtorque between both engines, even during vigorous maneuvers.[3] Power management has been greatly eased via the addition of an automatic engine-governor system, allowing pilots to simply monitor the torque and engine temperature gauges. The aircraft can be suitably equipped for flight underinstrument flight rules (IFR) as well as for single-pilot operations.[3]
According to aviation publicationFlying, as a consequence of its uncommon rigid mainrotor system, the BK 117 possessed relatively high stability and maneuverability which, amongst other capabilities, reportedly gave the type the ability to perform a steeper approach than any other helicopter in its class.[3] The four-bladed main rotor was smaller and slower-turning than many of its contemporaries, reducing both vibration and noise while also enabling the type to use more compact landing sites. The high-mounted tail boom and tail rotor of the BK 117 also presented several benefits, such as enhanced safety to personnel on the ground.[12] In terms of its flight performance, the type was considered to be suitable for the execution of variousaerobatic maneuvers, such as flying loops and rolls, while retaining such levels of inherent stability that pilots could readily release both thecyclic andcollective controls, unlike the majority of rotorcraft.[11] An optionalSperry-built three-axis stability augmentation system also served to improve the rotorcraft's ease of handling.[11]
![[icon]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.m.wikipedia.org%2fwiki%2fFile%3aWiki_letter_w_cropped.svg) | This sectionneeds expansion. You can help byadding missing information.(November 2017) |
A BK 117-B2 helicopter contracted by theNew South Wales Rural Fire Service to fight fires crashed on 17 August 2018, the pilot died in the crash.[13]
A BK 117-B2 helicopter owned byAir Methods LLC crashed on 24 April 2025 during takeoff near the runway, of the 3 people aboard all survived.[9]
A BK 117-B2 helicopter owned byAirmedic crashed on 20 June 2025 during takeoff in a lake, of the 5 people aboard, 4 died, including the patient.[1]
A BK 117-D3 helicopter owned by Eastindo Air crashed on 1 September 2025 near a waterfall, of the 8 aboard, all were killed.[14]
A single BK 117 A-3 (c/n 7106) was leased by theCanadian Forces Air Command for a test program and designated as theCH-143. When the program was over, the aircraft was returned to MBB Canada.[15]
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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 theEC145 or H145. Nevertheless, all models share the same EASA Type Certificate (see EASA Type Certificate Data Sheet).[20]
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The majority of the helicopters are operated by various emergency services although it is also operated by private individuals, companies and executive charter operators.
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Data fromJane's All The World's Aircraft 1993–94[55]
General characteristics
Performance
Related development
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Airbus Helicopters aircraft | ||
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| Civil helicopters |
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| Military helicopters |
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| Experimental helicopters | ||
