Where is my Airplane?


Some ask for better ways to track and locate civil aircraft in emergencies.


Flying search patterns in Northern Arizona together with other flightschool aircraft looking for an aircraft, a good friend and his students is not a pleasant task. We did not care about the glorious landscape as we looked out and listened to 121.5 Mhz trying to get a signal. I was an instructor at Embry-Riddle Aeronautical Univeristy in Prescott, Arizona in the early 80s and one of us was missing after a night flight. The flightplan had been closed with the FSS shortly before landing. Thank God later in the day we heard that all had survived. The instructor had walked to the next settlement for many hours in shock before he could call operations. He had overlooked a ridge in the dark night during the descent and hit the trees.


As we got to know our first aircraft as student pilots, it was good to learn that there was an ELT, the Emergency Locator Transmitter that sends a signal on 121.5, 243.0 and 406.025 Mhz if the aircraft crashes or the transmitter is manually activated after a forced landing. Somebody would hear us, somebody would know, and they would come to get us.


Many pilots make it a habit to monitor 121.5Mhz on their second VHF set. Especially at turbojet cruise altitudes a large area is covered, and any emergency transmissions or ELT signals are well received. Any signal is usually reported to ATC, and even though there are a lot of nuisance signals due to ELT testing or inadvertent activation over domestic airspace, on overwater and especially remote polar routes this routine monitoring by pilots still has great significance in alerting rescue coordination centers.


The potential of satellites to receive these signals was recognized early, and since the 1982 western and communist countries cooperated in this specific area. The COSPAS-SARSAT system uses LEO (Low Earth Orbit) and geostationary weather satellites to pinpoint the location of an accident. The advantage of the LEO satellites is that they can cover the polar regions beyond 70 degrees latitude. Using the Doppler effect, the location of a signal can be calculated within four hours at the most with the help of these satellites. The original COSPAS-SARSAT system used only LEO satellites. As there were many nuisance ELT alerts, costly SAR efforts were launched too many times. The new 406 MHZ ELTs, required since 2008, must be registered with the state of registry of the aircraft. They transmit the aircraft registration, position and more data on 406.025Mhz. The frequencies 121.5 and 243 Mhz are used by SAR vessels for homing. Any alert between 70N and 70S latitudes is received immediately by the geostationary satellites and relayed to rescue coordination centers. A quick phonecall to the aircraft operator then allows a verification of the alert.


A central feature of any ELT, as well as EPIRBS (Emergency Position Indicating Radio Beacon), their maritime equivalent, is automatic activation. In the case of EPIRBS, this is done by a hydrostatic switch, which releases and activates the unit if it is a few meters below the water so that it may float up and begin to transmit. Aircraft ELTs are either automatically activated by a G-switch upon impact or contact with water. They are not designed to float up as many crashes occur on land or aircraft float for a while before they sink. Aircraft do have, however, ULBs (underwater locator beacons) for the cockpit voice recorder (CVR) and the flight data recorder (FDR). These devices emit an ultrasonic pulse once per second at 37.5 khz which can be received underwater up to one or two miles away. Accident investigators recommend the installation of ULBs that also transmit at a lower frequency to achieve ranges of 5-10 miles. ULBs are battery powered and can only pinpoint the exact location. SAR units need to have a rough idea where the wreckage is before they begin the search. And they only have 30 days to find the site, as the batteries are certified for this timeframe.


Which brings us to the big question: Why was there no ELT signal received from MH370. According to information available to the public, no ELT signal was received from MH370 after its disappearance on March 8th, 2014, and nothing at all has been received or found since then. There are only a few possible reasons why a signal was not received. If you believe in an accident such as an electronics bay fire, the most likely reason is that the aircraft broke into pieces and sank quickly enough to make ELT signal transmission impossible. Others are that the ELT malfunctioned, was switched off or that there was no crash at all. The latter two imply willful sabotage and lead us into speculation, which is not serious with information available at this point.


However, there is another possibiltiy: Maybe there was no ELT with a G-switch installed. If you are surprised you should look at US aviation law and regulation again. The Federal Aviation Act requires all civil aircraft to install ELTs, with the major exception of "aircraft when used in scheduled flights by scheduled air carriers holding certificates issued by the Secretary of Transportation….". The reasoning behind this is that US scheduled air carriers are so well covered by radar and other monitoring devices that the location of an accident will be known quickly. For overwater flights, automatic ELTs are required, but automatic includes portable water-activated ELTs, so fixed installed ELTs with G-switches are not installed in a lot of US airline jets. And as US regulation influences foreign regulation tremendously if it is not outright copied, there is a realistic chance that The B777 of MH370 did not have an ELT installed. It should be noted though that since a number of years new airline jets are fitted with fixed automatic ELTs again.


Knowledge about ELTs and their limitations belongs to any serious aircraft tracking discussion, as it shows that this is not a new topic. Authorities always wanted to know where aircraft were, mostly for collision avoidance but also for safety and security reasons. Position reporting by voice transmission was and is a reliable technique, and primary radar has been a mainstay of tracking since since the World War 2. Secondary radar using transponder returns is part of our every day lives as pilots and seen as helpful by most.


Over oceans and remote territories, aircraft used to transmit their postitions and intentions by HF voice, but since more then 10 years this has been mostly replaced by controller pilot datalink communication (CPDLC), an oceanic variant of ADS-B using satellite links. Many aircraft are also online with internet connectivity or Inmarsat phone and datalink service. Aircraft data are routinely transmitted to maintenance centers, not only for airline jets but also for larger and newer executive jets. Upper air weather data are collected and forwarded to weather centers every 30 minutes by automatic weather transmissions. All these data transmissions always include LAT/LONG position, altitude, airspeed, temperature and a multitude of other data.


The complete disappearance of a transport category aircraft is thus impossible – unless you include sabotage and terror in your analysis. As all aircraft systems are certified by the FAA and the authorities of other countries, they have to fulfill certain standards to be installed and used in an aircraft. These standards are high, and all kinds of possible emergency scenarious are considered. Fire, and especially electrical fires and short circuits are a major issue. Therefore, all electrical systems can be switched off from the cockpit if problems arise. Non essential items such as passenger entertainment and ovens are usually grouped on the utility bus. One or two switches on this bus allow the flightdeck crew to turn all this equipment off if needed. The broadband antenna for inflight internet is also controlled by a switch on the flightdeck, for good reason as there is a broadband smoke procedure on aircraft equipped with this system.


Only purely battery equipped systems can not be switched off, but are also not operating under normal circumstances. These are the portable ELTs and the FDR and CVR pingers.


There a number of companies that offer satellite tracking by battery powered units, mostly for non-aviation use. I spent a few weeks this summer on a beautiful tall ship, the “Alexander von Humboldt II” in the Norwegian sea. As we were racing other windjammers, the organizers of the event had partnered with a company called Yellowbrick to track the race’s progress and to display it on a website for all to see. The Yellowbrick unit looked just like a yellow brick should look like and was strapped to a railing on the bridge with a velcro strip. Every half hour or so it sent an updated GPS position to the Iridium satellite network, powered by batteries and completely independent of the ship it was attached to.


The Iridum satellite system was conceived by Motorola engineers in the late 80s. It consists of 56 low earth orbit (LEO) satellites with an orbital inclination of 86.5 degrees. The system covers the entire Earth including the polar regions and allows anyone with a handheld satellite phone not much bigger then a regular cellphone to make phonecalls from any location on this planet. This design was far ahead of its time and a financial failure. Motorola sold Iridium to investors, very happy to get rid of it. It turned out however, that the investors made a smart move. They marketed the system to governments, mining and oil companies and western military forces. Today, no one questions the value of Iridium.


Iridium allows the development of a new technology called active aircraft tracking. Sometimes called “bread-crumb” approach to SAR, these systems continously transmit positions like bread crumbs a bird or mouse would follow. If the transmission suddenly stops, the most likely position of the vessel is known to ground stations, as well as its speed, direction and altitude. A confirmation call to the registered operator can help to weed out false alarms such as those caused by bad signal reception.


Another system that may be used for active tracking in certain areas is the SPOT system. It is similar to Yellowbrick in many ways, but uses the Globalstar satellite system. Globalstar satellites orbit in a low Earth orbit at an inclination of 52 degrees and do not cover the polar regions. The high seas are also not covered, as calls are routed from the satellite directly to a land station. If the satellite sees a vessel but a land station is not within reach from the satellite, no call can be made. Iridium satellites will send the call to other satellites in orbit if no Earth station is available. Iridium to Iridium calls are even routed directly through satellites without the use of land stations.


Calls for mandatory continous tracking of aircraft with completely independent systems that have been in the headlines in recent months ignore the regulatory and technical hurdles for such a system to be certified, as well as the costs involved. Active tracking is certainly something to think about. Wether a new satellite constellation or an existing one like Iridium will be right for the job needs to be seen. For example, the high velocity of jet aircraft may be a problem for the Iridium satellites as vessels pass from satellite to satellite quickly.


But my support for active tracking ends if it is made mandatory, or if the electrical power supply cannot be controlled from flightdeck. Many private individuals and companies do not wish data about their travels to be available to more then a few trusted people. And battery powered units with no cockpit switch can cause major problems. A recent example is the Ethiopian B787 that caught fire while parked on the apron of London’s Heathrow airport. The culprit was actually the ELT itself, a battery powered unit that uses a lithium-manganese battery. The FAA issued an airworthiness directive regarding the installation and wiring of these ELTs, that seemingly are able to create the emergency that they are built to report entirely by themselves.


Our main concern should be safety and not sophisticated sabotage. A well selected and trained crew in a well designed and maintained aircraft is still the best guarantee for the safety of the passengers. Instead of trying to foolproof the aircraft against saboteurs from within, it is much better to foolproof the hiring against illoyal, incompetent and otherwise challenged crewmembers. Good people are always a good investment.



J. Peter Berendsen