Before the 1960s, wilderness airplane crashes usually ended in tragedy. Even if they were not seriously injured during the crash, survivors faced a long wait before they could be rescued, often succumbing to starvation or exposure to the elements before they could be saved.

Rescue crews had a hard time finding crash survivors obscured by brush and snow. They were forced to fly dangerously low, searching by eyesight alone for an SOS or signs of smoke. Often, rescue crews flew in the same dangerous conditions that caused the original accident, causing many rescuers to face the same fate as the crash victims.

For one National Research Council engineer, however, this harsh reality was simply unacceptable. So Harry Stevinson invented the Crash Position Indicator to help rescue crews find downed aircraft quickly and safely – a device that would save the lives of crash victims and rescue crews alike.

Tired of airplane rescue tragedies

Harry Stevinson grew up hearing tragic tales of rescue missions gone wrong, and he wanted to do something about the problem. Drawing from his extensive knowledge of radios, Stevinson knew it was possible to distinguish the direction from which radio waves came. He decided the solution to finding downed aircraft would be a radio beacon on each aircraft that could indicate where the plane had crashed.

Harry Stevinson displays the Crash Position Indicator.

His plan required that the radio beacon survive the impact of a plane crash, as well as any fires, explosion or water immersion that followed – and of course, it had to keep working through all hazards.

Unfortunately, as determined as Stevinson was to improve wilderness rescue attempts and develop his radio beacon idea, the project had to be put on hold when the Second World War began.

Renewed determination to save lives

After the war, in 1946, Stevinson was studying gliders at the NRC Flight Research Lab. During test flights, gliders would descend from high altitudes while Stevinson recorded data about how the aircraft "handled" in different situations.

While these tests were ongoing, a jet fighter happened to crash. Stevinson and his team watched helplessly as the rescue crew that was searching for the lost plane also crashed into the bush. To Stevinson, it was clear that had a radio beacon been installed on the downed jet the task of locating the crash site would have been much easier and safer for the rescue crews. Once again, he was determined to create a radio beacon for downed aircraft.

Developing a crash-proof radio beacon was no easy task, however. The final device needed to meet some tough requirements: it had to ride on the host aircraft in an inactive state for indefinite periods, but be ready to immediately start to work in the event of a crash; it had to survive any conceivable crash by falling clear as the aircraft crumpled; and it had to turn itself on automatically, so that rescuers could find the location of the crash quickly. In addition to these basic requirements, it had to be lightweight and low-cost.

The Crash Position Indicator

In the end, Stevinson built a device that combined the radio transmitter and antenna in one compact package. It was light and durable, designed to attach to the tail of an aircraft, then separate and curve away from the plane during a crash. A spring-loaded latch that held the beacon to the airplane would release on impact, allowing the beacon to be carried safely away from the plane by the rushing wind.

Stevinson's device was tested in situations where searchers did not know the location of the fallen aircraft. In every test, searchers found their target in less than two hours – an unbelievable improvement in search and rescue abilities.

By not giving up on his goal of designing a radio beacon for locating aircraft, NRC's Harry Stevinson improved aviation safety and saved lives around the world.