Spectrum Management - From the Early Years to the 1990s

by Laval Desbiens

Locating Emergency Locator Transmitter  (ELT's & EPIRB's)

A contribution from Michel Castonguay

ELT = Emergency Locator Transmitter

EPIRB = Emergency Position-Indicating Radio Beacon

The airlines, government and the public as a whole are concerned with aviation safety.  One way to increase aviation safety consists in equipping each aircraft with an automatic locator beacon, better known as an ELT (Emergency Locator Transmitter).

This locator beacon is designed to transmit a radio signal when it sustains a strong enough shock. It uses radiolocation to pinpoint an aircraft's position.

The International Telecommunication Union (ITU) and the International Civil Aviation Organization (ICAO) have reserved the 121.5 MHz and 243 MHz frequencies world-wide to standardize the use of this device.

Air traffic controllers in airports monitor these frequencies continuously. An international network of satellites has also been put in place to ensure automatic, approximate location of the source of the distress signal. But who has enough experience and equipment to locate missing aircraft through emergency signals on the 121.5 MHz or 243 MHz frequencies? In Canada, the military and some technicians at Transport Canada are able to do so, as well as radio inspectors.

It must be understood that the situation has evolved greatly since the implementation of this safety system and that in the beginning, few people were qualified to detect and locate the source of these signals. Satellites did not have the capacity they have nowadays and the quality of the locator beacons was not as good. During the early years of implementation, the batteries of ELTs tended to become defective and trigger accidental operation of the emergency transmitter. Since all the devices use mainly the same frequency, the interference caused by those that were transmitting a signal because of a defect or malfunction hindered reception to a great extent and reduced the monitoring network's ability to identify an aircraft in distress.

In a typical search procedure, a distress signal is detected by an air traffic controller, an airplane pilot or military personnel who report the information to the Canadian Search and Rescue Centre. The distress signal is located by the satellite network and military aircraft that determine the position of the ELT of the aircraft in distress or that has a malfunction. When conditions (weather, urban areas, airports) do not allow military personnel to pinpoint the aircraft involved, they ask technicians at Transport Canada or radio inspectors to locate the device that is transmitting the distress signal.

During the early years of implementation, the number of malfunctions was quite high. The military would locate the sources of distress signals, but very often could not tell which aircraft were in trouble because they were in airports, on water, in hangars or in urban areas. Thus, radio inspectors were often called in to complete the job of finding the aircraft. Below are a few cases and anecdotes that clearly depict the nature of the investigations carried out to find emergency locator transmitters.

1- Typical case

The majority of investigations would start with a call from the Canadian Search and Rescue Centre to inform a supervisor in the district office concerned of the department responsible for managing radio frequencies (Transport Canada, Communications Canada, Industry Canada) that the Centre was receiving a signal from an ELT. Military personnel had reached the area aboard a Buffalo aircraft and had traced the source of the signal to a certain spot, but they had not found any aircraft in distress. They were requesting assistance to find the malfunctioning ELT in the identified area.

Regardless of the time of day, the supervisor would promptly assign the investigation to a radio inspector who would start by going to the office to collect a spectrum monitoring vehicle and the required radiolocation equipment. He would then contact the search and rescue centre to validate the information and the continued presence of the distress signal. He would travel towards the area identified by the military and begin to monitor the 121.5 MHz frequency with the radiolocation equipment. After reaching the area in question, the receiving equipment installed in the monitoring vehicle normally allowed the distress signal to be picked up and the radio inspector could find the position of the ELT quickly enough by using direction finding methods (azimuth readings, triangulation, field intensity measurements, etc.). The problem, in most cases, was that the aircraft containing the malfunctioning locator beacon was parked among many other planes in an airport or float planes on water, or it could not be seen because it was in a hangar or a garage of some sort. The radio inspector would then have to use various investigation techniques and considerable resourcefulness to identify the aircraft concerned.

Once it was identified, he had to stop the transmission of the interfering signal as quickly as possible to clear the distress frequency of all interference. Then, he would contact the Search and Rescue Centre to report the results of the investigation. This type of investigation led to the discovery of malfunctioning or faulty ELTs in many airport hangars, commercial and private garages where aircraft were being repaired, at marinas and isolated airports, in parts warehouses and even in containers ready for shipment to Russia.

2- Where did the plane go?

After being informed by air traffic controllers at Dorval Airport in Montreal that they were receiving a signal on the 121.5 MHz frequency, a radio inspector from the Montreal district office who was working in the area rushed to the airport and quickly determined that the ELT transmitting the distress signal was located in a hangar where four large aircraft were parked side by side.

The inspector had only radio monitoring equipment that was permanently installed in his vehicle and he could not tell which of the aircraft was at fault due to the metallic environment that produced multiple reflections of the signal. He went to the airline company's office and called a colleague at his office to bring him the necessary portable radio monitoring equipment. When the colleague arrived with the equipment 45 minutes later, the distress signal could no longer be detected, but the inspector noted that one of the aircraft had left the hangar. The inspector provided the air traffic controllers with the identification of the aircraft in question and they indicated that the plane had taken off. Measures were taken to inform the Canadian Search and Rescue Centre and the pilot concerned of the problems with the ELT so that it could be corrected upon arrival.

3- Happy New Year!

The Canadian Search and Rescue Centre performs extraordinary tasks and the military provides assistance that is beyond measure. However, their response capacity is limited by weather conditions, and sometimes their planes cannot be used.

This was the case at the end of one New Year's Day when a distress signal was detected by the satellite network, which determined the position to be halfway between Ottawa and Montreal. A major snowstorm was in progress and the icy cold prevented the Buffalo aircraft that were assigned to these searches from taking off in Trenton. The authorities at the Centre contacted the staff on call at the district office in Montreal and a radio inspector was assigned to investigate the case. The inspector went to the office and set out for the identified area in a car equipped with direction finding equipment. The storm was quite fierce and made driving difficult: the temperature was very cold, the wind was very strong and snow was piling up in large quantities. Braving the bad weather, the radio inspector took the road along the Ottawa River to Hull.

Because of these conditions, the search lasted many hours but the inspector finally located the aircraft transmitting the distress signal. It was a small, unoccupied Cessna sitting strangely on the ice close to the shore of the Ottawa River near the town of Fawcett, Quebec, with one of its propellers broken. As night had fallen and visibility was almost nil, the inspector consulted the authorities at the Canadian Search and Rescue Centre and grounded the antenna to limit transmission of the distress signal. He decided to wait until dawn to continue the investigation and then questioned some people at a nearby restaurant to determine the circumstances of the incident.

The restaurant owner explained that the pilot of the plane had shown up at his restaurant the day before and had asked him for help. The facts were difficult to believe but turned out to be true. The pilot had left Ottawa, heading for his home in Valleyfield, and had made an emergency landing on the frozen river because his carburetor was icing up due to the cold. Since there was a thick layer of snow on the river, he had asked the restaurant owner for help and some friends had towed the plane on toboggans with snowmobiles. The pilot had cleaned his carburetor and had decided to take off again in spite of the bad weather. As he was not on an airport strip and lacked good judgment, he had decided to tie the toboggans under the plane's wheels and tried to take off from the snow-covered river. What was bound to happen happened: the plane did not take off and nosedived. One of the propellers broke and the same snowmobilers towed the plane back to the shore. The pilot had called his home and someone had come to get him by car.

What a story... certainly befitting someone who was not an experienced pilot! The radio inspector visited the pilot upon his return to validate this strange story and submitted a detailed report to the authorities at Transport Canada.

4- A roving beacon ...

One day, the Canadian Search and Rescue Centre requested the help of a radio inspector from Communications Canada because a distress signal had been detected by the satellite network and the signal had been traced to the Montreal airport. They had contacted Transport Canada, which had been unable to determine the position of the signal and no aircraft was in distress.

The radio inspector sent to the scene was able to detect the distress signal but, strangely enough, it was coming from the main airport building. The inspector then headed towards the terminal with portable radio monitoring equipment and tried to determine the exact location of the source of the signal. The task was particularly difficult because the source of the signal was constantly on the move. After a few hours of searching, the source finally stopped moving and the inspector determined that the signal was coming from the suitcase of an airplane pilot. In fact, it was a portable ELT belonging to the pilot who was carrying it in his suitcase to bring it to a repair shop. The locator beacon was defective because it transmitted continuously without being activated. The pilot was very surprised and disconcerted, and the signal was finally eliminated after the battery was disconnected.

5- Is the pilot still in the plane?

One night, the Canadian Search and Rescue Centre requested the assistance of Communications Canada because a distress signal had been detected by the satellite network and traced to the Laurentian region. The stormy weather conditions prevented the Department of Defence rescue personnel from heading to the area with their planes and they could not locate the source of the signal.

A radio inspector was called back to work and sent to the scene as quickly as possible. The inspector headed towards the coordinates provided by the Search and Rescue Centre and succeeded in locating the source of the distress signal. It was still night and the signal came from the middle of a lake near the town of Rawdon.

It was so dark due to the storm that it was impossible to determine the presence of a plane. After patrolling all around the lake, the inspector finally identified a float plane lying upside down in the lake. The inspector then contacted the police department serving the area

and learned that a resident had saved the pilot a few hours earlier, after the float plane had flipped during take-off. The pilot had been rescued at the last minute thanks to a Good Samaritan who had rushed by boat to the overturned float plane and had pulled the unconscious pilot from the submerged cabin.

The hero had saved the pilot's life by applying resuscitation techniques and the pilot had been taken to the hospital. The tale ended on a happy note because the radio inspector could have discovered a fatality.

Michel Castonguay

2004

by Laval Desbiens