Crash Position Indicator
Encyclopedia
The Crash Position Indicator (CPI) is a radio beacon designed to be ejected from an aircraft when it crashes. This helps ensure it survives the crash and any post-crash fires or sinking, allowing it to broadcast a homing signal to search and rescue
aircraft.
CPI's became a requirement on some military aircraft and were often combined with flight data recorder
s. Today the beacon functions are normally fulfilled by the Emergency Locator Transmitter system. The term "crash position indicator" no longer refers to the specific device, but any locator beacon. The CPI is ranked #48 in the list of the 50 Greatest Canadian Inventions.
. After the war he joined the National Research Council's (NRC) National Aeronautical Establishment (NAE), testing glider
performance.
While these tests were ongoing, a jet fighter happened to crash. The aircraft had no beacon, and thus the rescue plane sent to find the fighter was forced to fly low over wooded areas in an attempt to locate the wreck. The rescue plane's low flight led to its own crash in the bush. With a beacon, the rescue aircraft would have been able to stay at much higher, and safer, altitudes. Stevinson decided that the beacon was more important than glider research, and was able to convince the NRC to develop the concept.
Other rescue beacon systems had already been developed and deployed, but Stevinson felt these were insufficient. If the crash occurred over water, the beacon would sink with the aircraft even if the crew escaped and were on the surface. Over land, the aircraft itself would block the signal if the beacon ended up buried under the fuselage, and the crash and any post-crash fires had the possibility of destroying it.
There was one contemporary system that offered survivability. It used a small mortar
to fire the beacon off the aircraft and then land it under parachute
with a shock absorber
to lessen impact with the ground. The beacon package included a folding antenna, two pop-out arms intended to orient it upright after landing on the ground, and a floatation bag for water.
The key, however, was to make an aerodynamic system that would pull the system away from an aircraft quickly, but then slow the CPI down once it was released. Working with David Makow, Stevinson came up with the idea of using a Frisbee
-shaped package, built a model out of paper, and dropped it off the balcony. When it exhibited a tumbling motion, a second model was built of aluminum and released from the window of a car. As hoped, the tumbling quickly slowed the package to safe speeds. The team then started work on a radio-clear version using fiberglass reinforced plastic.
While they worked on the design, the Division of Electrical Engineering was working on a production radio system. After about two years of development, everything was ready and the first experimental CPI was assembled. Among the many tests, early examples were fired on a rocket sled
at speeds up to 370 km/h off the top of a cliff formed by a former gravel pit.
These tests were followed by production-setting releases from aircraft. In this case the CPI was placed inside a cylindrical recess on the outside of the aircraft fuselage, normally near the tail. The upper curved portion of the CPI projected into the wind, providing a constant lift when the aircraft was in motion. This was countered by a spring latch that would automatically release in the case of a sudden deceleration.
. They contracted Leigh Instruments of Carleton Place to manufacture the system.
CPI was soon mandatory on Canadian Air Force aircraft working in the far north. In one instance, an aircraft in the Yukon
mountains was found by CPI in a location where visual location would have been impossible. In another, a USAF aircraft crashed into the ocean at night, but its injured crew was rescued after the CPI broadcast was detected. Leigh received a letter of thanks. Even Air Force One
was equipped with a CPI, the AN/ASH-20.
under the name "Flight Memory". In 1958 he visited the NRC to discuss the possibility of incorporating the Flight Memory system into the CPI.
At the time, Warren's device had not been built, and when they finally had a unit ready for testing in 1962, they found that DSI had already developed a "very nice" system providing "voice, time, and 96 data channels … on ¼ inch tape." Surprised by this development, ARL nevertheless requested one of the airframes, and showed it with Flight Memory at a trade show in 1963.
DSI's system would go on to spawn a series of models, some in CPI's and some in ruggedized crash-survivable forms.
. It was optional on many other aircraft, and fairly common on bush planes. Its success was such that Leigh eventually purchased DSI, and by 1978 yearly sales of modern CPI devices were $6 million. Total sales over the years topped $100 million. Leigh became one of the largest Canadian electronics firms.
In 1988, Plessey
announced they would purchase Leigh for about 42.5 million Pounds. This was most of the money Plessey received from GEC during the creation of GEC Plessey Telecommunications
. However, the deal fell through and the company was eventually broken up.
Although most aircraft carry non-ejectable beacons, ejectable versions are still built for overwater flight, and most of these feature the tumbling-airfoil design.
Search and rescue
Search and rescue is the search for and provision of aid to people who are in distress or imminent danger.The general field of search and rescue includes many specialty sub-fields, mostly based upon terrain considerations...
aircraft.
CPI's became a requirement on some military aircraft and were often combined with flight data recorder
Flight data recorder
A flight data recorder is an electronic device employed to record any instructions sent to any electronic systems on an aircraft. It is a device used to record specific aircraft performance parameters...
s. Today the beacon functions are normally fulfilled by the Emergency Locator Transmitter system. The term "crash position indicator" no longer refers to the specific device, but any locator beacon. The CPI is ranked #48 in the list of the 50 Greatest Canadian Inventions.
Harry Stevinson
The CPI was developed by Harry Stevinson, starting work on the concept just before the opening of World War IIWorld War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
. After the war he joined the National Research Council's (NRC) National Aeronautical Establishment (NAE), testing glider
Glider
Unpowered aircraft are a group of aerial vehicles that can fly without onboard propulsion. They can be classified as gliders, balloons and kites. In this instance, 'flight' means a trajectory that is not merely a vertical descent such as a parachute. In the case of kites, the flight is obtained by...
performance.
While these tests were ongoing, a jet fighter happened to crash. The aircraft had no beacon, and thus the rescue plane sent to find the fighter was forced to fly low over wooded areas in an attempt to locate the wreck. The rescue plane's low flight led to its own crash in the bush. With a beacon, the rescue aircraft would have been able to stay at much higher, and safer, altitudes. Stevinson decided that the beacon was more important than glider research, and was able to convince the NRC to develop the concept.
Other rescue beacon systems had already been developed and deployed, but Stevinson felt these were insufficient. If the crash occurred over water, the beacon would sink with the aircraft even if the crew escaped and were on the surface. Over land, the aircraft itself would block the signal if the beacon ended up buried under the fuselage, and the crash and any post-crash fires had the possibility of destroying it.
There was one contemporary system that offered survivability. It used a small mortar
Mortar (weapon)
A mortar is an indirect fire weapon that fires explosive projectiles known as bombs at low velocities, short ranges, and high-arcing ballistic trajectories. It is typically muzzle-loading and has a barrel length less than 15 times its caliber....
to fire the beacon off the aircraft and then land it under parachute
Parachute
A parachute is a device used to slow the motion of an object through an atmosphere by creating drag, or in the case of ram-air parachutes, aerodynamic lift. Parachutes are usually made out of light, strong cloth, originally silk, now most commonly nylon...
with a shock absorber
Shock absorber
A shock absorber is a mechanical device designed to smooth out or damp shock impulse, and dissipate kinetic energy. It is a type of dashpot.-Nomenclature:...
to lessen impact with the ground. The beacon package included a folding antenna, two pop-out arms intended to orient it upright after landing on the ground, and a floatation bag for water.
CPI development
Stevinson liked the idea, but not the implementation. He preferred an aerodynamic release system that would eliminate the mortar, and a ruggedized radio system with an omnidirectional antenna that would eliminate the rest of the complexity. Survivability on both land and water could be achieved using lightweight foams.The key, however, was to make an aerodynamic system that would pull the system away from an aircraft quickly, but then slow the CPI down once it was released. Working with David Makow, Stevinson came up with the idea of using a Frisbee
Frisbee
A flying disc is a disc-shaped glider that is generally plastic and roughly in diameter, with a lip. The shape of the disc, an airfoil in cross-section, allows it to fly by generating lift as it moves through the air while rotating....
-shaped package, built a model out of paper, and dropped it off the balcony. When it exhibited a tumbling motion, a second model was built of aluminum and released from the window of a car. As hoped, the tumbling quickly slowed the package to safe speeds. The team then started work on a radio-clear version using fiberglass reinforced plastic.
While they worked on the design, the Division of Electrical Engineering was working on a production radio system. After about two years of development, everything was ready and the first experimental CPI was assembled. Among the many tests, early examples were fired on a rocket sled
Rocket sled
A rocket sled is a test platform that slides along a set of rails, propelled by rockets.As its name implies, a rocket sled does not use wheels. Instead, it has sliding pads, called "slippers", which are curved around the head of the rails to prevent the sled from flying off the track...
at speeds up to 370 km/h off the top of a cliff formed by a former gravel pit.
These tests were followed by production-setting releases from aircraft. In this case the CPI was placed inside a cylindrical recess on the outside of the aircraft fuselage, normally near the tail. The upper curved portion of the CPI projected into the wind, providing a constant lift when the aircraft was in motion. This was countered by a spring latch that would automatically release in the case of a sudden deceleration.
Commercial production
When development was completed in 1959, production did not start immediately. Licenses were passed from company to company before finally settling at Dominion Scientific Instruments (DSI) of OttawaOttawa
Ottawa is the capital of Canada, the second largest city in the Province of Ontario, and the fourth largest city in the country. The city is located on the south bank of the Ottawa River in the eastern portion of Southern Ontario...
. They contracted Leigh Instruments of Carleton Place to manufacture the system.
CPI was soon mandatory on Canadian Air Force aircraft working in the far north. In one instance, an aircraft in the Yukon
Yukon
Yukon is the westernmost and smallest of Canada's three federal territories. It was named after the Yukon River. The word Yukon means "Great River" in Gwich’in....
mountains was found by CPI in a location where visual location would have been impossible. In another, a USAF aircraft crashed into the ocean at night, but its injured crew was rescued after the CPI broadcast was detected. Leigh received a letter of thanks. Even Air Force One
Air Force One
Air Force One is the official air traffic control call sign of any United States Air Force aircraft carrying the President of the United States. In common parlance the term refers to those Air Force aircraft whose primary mission is to transport the president; however, any U.S. Air Force aircraft...
was equipped with a CPI, the AN/ASH-20.
ARL's Flight Memory
While Stevinson was working on the "tumbling aerofoil beacon", David Warren of the Aeronautical Research Laboratories (ARL), Australia's counterpart to the Canadian NAE, was developing the concept of the cockpit voice recorderCockpit voice recorder
A cockpit voice recorder , often referred to as a "black box", is a flight recorder used to record the audio environment in the flight deck of an aircraft for the purpose of investigation of accidents and incidents...
under the name "Flight Memory". In 1958 he visited the NRC to discuss the possibility of incorporating the Flight Memory system into the CPI.
At the time, Warren's device had not been built, and when they finally had a unit ready for testing in 1962, they found that DSI had already developed a "very nice" system providing "voice, time, and 96 data channels … on ¼ inch tape." Surprised by this development, ARL nevertheless requested one of the airframes, and showed it with Flight Memory at a trade show in 1963.
DSI's system would go on to spawn a series of models, some in CPI's and some in ruggedized crash-survivable forms.
Commercial success, business failure
By the 1970s, the CPI with data recorder was now a standard item on many Canadian and US aircraft, and would also be selected for the Panavia TornadoPanavia Tornado
The Panavia Tornado is a family of twin-engine, variable-sweep wing combat aircraft, which was jointly developed and manufactured by the United Kingdom, West Germany and Italy...
. It was optional on many other aircraft, and fairly common on bush planes. Its success was such that Leigh eventually purchased DSI, and by 1978 yearly sales of modern CPI devices were $6 million. Total sales over the years topped $100 million. Leigh became one of the largest Canadian electronics firms.
In 1988, Plessey
Plessey
The Plessey Company plc was a British-based international electronics, defence and telecommunications company. It originated in 1917, growing and diversifying into electronics. It expanded after the second world war by acquisition of companies and formed overseas companies...
announced they would purchase Leigh for about 42.5 million Pounds. This was most of the money Plessey received from GEC during the creation of GEC Plessey Telecommunications
Marconi Communications
Marconi Communications was a principal subsidiary of the Marconi Corporation plc and was formerly known as GEC Plessey Telecommunications . The company was a world leading telecommunications manufacturer...
. However, the deal fell through and the company was eventually broken up.
Although most aircraft carry non-ejectable beacons, ejectable versions are still built for overwater flight, and most of these feature the tumbling-airfoil design.