Three major aviation tragedies in the past five years, all of which occurred above open ocean water and left rescue teams frantically searching for the crash sites, have put the technology designed to locate the wreckage firmly in the spotlight.
Similar to the as-yet unexplained Malaysia Airlines MH370 accident and the 2009 Air France 447 disaster, the crash of Air Asia flight QZ85021 highlighted once again the shortcomings in the design operational mode of emergency beacons, the Emergency Locator Transmitters (ELT), that are part of the equipment of almost every commercial aircraft.
The beacons, triggered either automatically upon impact or manually by the pilot of a plane in distress, transmit an SOS signal via Cospas-Sarsat receivers currently on six low-Earth polar orbiting and six geostationary satellites. They are designed to immediately alert authorities to a disaster and help despatch rescue teams promptly to increase the chances of finding survivors.
“Indeed, the most challenging aviation scenario for Cospas-Sarsat is a crash in water with rapid submersion,” says Steven W Lett, Head of Secretariat of Cospar Sarsat. “We believe that in those three incidents the beacons may have been triggered, but that the aircraft submerged before the distress signal could be sent.”
When 'now' is too late
For various technical and operational reasons, the current generation of ELTs requires about 50 seconds to send the first burst of data containing the exact GNNS coordinates of the crash.
“These beacons are essentially made for crashes on land and they are not very well suited for crashes on water,” says Milan Cermack, Memorial University of Newfoundland researcher and research associate with the Offshore Safety and Survival Centre.
“The major problem is the activation of the beacon in flight. The way it works now, the beacon can be either manually activated from the cockpit or, if that doesn’t happen, you have to wait until the actual impact. But even then it may not be triggered either because the aircraft sinks too fast or because it impacts under a very flat angle without sufficient force.” With a very violent impact on land potentially followed by fire, the beacon itself might be destroyed.
There could be various reasons for pilots not activating the beacons manually when there would be still plenty of time for the distress signal to get through. Cockpit voice recorder data from the Air France Flight 447 that crashed in 2009 in the Atlantic revealed the pilots were actually completely unaware the plane had stalled and was hurtling downwards from the sky. Theories behind the as-yet unexplained MH370 disappearance suggest the pilots may have been incapacitated due to decompression and a subsequent lack of oxygen in the cabin. What happened in the ill-fated Air Asia crash on 28 December 2014 remains to be seen.
The aviation industry, Cermack says, has been aware of the problems and discussed them on several occasions over the past years. However, it wasn’t until this recent string of tragic incidents and subsequent costly searches that the idea of a major upgrade to the system gained support.
In addition to the new generation of beacons capable of launching the transmission sequence in three seconds instead of the current 50, the industry is also studying the possibility of having the beacons triggered automatically while still airborne if substantial anomalies in flight data occur.
“Technically, you could take the information from the flight data recorder (FDR) and once you get into some flight mode that is not nominal – for example a simultaneous failure of both engines, explosive decompression, excessive rate of descent, abnormal flight attitudes like stalls, spins, or excessive bank angles - the flight data recorder could be programmed in such a way that it would automatically activate the ELT,” says Cermack.
“There are no fundamental technical showstoppers. The crucial reliability factor would be a careful selection of alarm-triggering criteria. To reduce potential false alarms, the crew should have a possibility to cancel the transmission of the distress signal if they regain control over the aircraft.”
Cermack believes the system would increase the success rate in cases such as the three ocean crashes of the past five years, where human activation as well as the automatic sequence failed.
“The in-flight activation was tested experimentally by (French aerospace agency) CNES in a parabolic flight,” Cermack says. “The results were not very accurate. However, they used the old Doppler method of location, using two passages of a low Earth orbit satellite. This isn’t a good solution for an aircraft in my opinion because in the aircraft you can use the GPS position which is embedded in the FDR. So you can feed the GPS position directly into the beacon.”
Beacon versus black box streaming
The idea may appear to be in direct competition with current proposals to introduce real-time aircraft tracking or partial streaming of black box data in commercial aircraft. But Cermack is confident the Cospas-Sarsat system is better suited to address emergencies and disaster situations.
“The current proposals expect streaming of some data about every 15 minutes. But that wouldn’t really help limit the area of a potential crash,” he says. “An airliner travelling at a groundspeed of approximately 900km/h will cover 225km every 15 minutes or 15km every minute. To achieve an instant location accuracy of 10km, the position information would have to be sent approximately every 40 seconds.”
Although such a service could theoretically run over the American satellite constellation Iridium, it would generate a huge amount of data, most of which would be of only limited use.
The updated Cospas-Sarsat system with the next-generation beacons and possible in-flight activation would, on the other hand, direct searchers to the site of the accident with pinpoint accuracy with only a few bursts of data at the critical moments.
Moreover, the system’s Mission Control Centres, connected to networks of Search and Rescue Services, are equipped to immediately despatch help to increase the chances for survivors.
Cospas-Sarsat’s technology was among those discussed in May last year at the UN International Civil Aviation Organisation’s meeting in Montreal, which addressed the challenges of global flight tracking in the wake of flight MH370's disappearance.
“Among the conclusions of that meeting was that Cospas‑Sarsat should be invited to continue to investigate, within its own programme and in partnership with the industry, the means of improving the reliability and utility of ELTs, particularly in the context of flight tracking during a distress event,” said Lett, citing the meeting’s outcome. “This work is underway within Cospas-Sarsat, and jointly among the Radio Technical Commission for Aeronautics (RTCA) and European Organisation for Civil Aviation Equipment (EUROCAE).”
Since its inception in the 1970s, the International Cospas-Sarsat Programme has helped save the lives of more than 35,000 people, including 5,032 passengers of mostly small aircraft.
The Cospas-Sarsat beacons transmit signal on the 406Mhz frequency, which in the case of the newer beacons equipped with a GNSS receiver, contains the exact coordinates of the accident. Alternatively, the beacons can be located by analysing the Doppler Effect affecting the beacon’s frequency as intercepted by the LEOSAR (low Earth orbit) satellites.
To improve coverage and transmission times, further search and rescue payloads are currently being sent to space on Galileo satellites to form what would become the MEOSAR (medium Earth orbit) segment of the Cospas-Sarsat system.
Cospas-Sarsat said it would investigate why the ELT’s were neither manually activated nor automatically triggered during the latest aviation disasters. However, it reassured the industry that in the case of another recent high-profile crash - the shooting down of Malaysia Airlines Flight 17 in Ukraine - the beacon worked as designed.
“In the crash of flight MH 17, the beacon was successfully triggered (apparently automatically) and was detected, possibly while the aircraft was still in the air and for many hours afterwards,” Steven Lett said.
Although statistically the odds remain low that another airliner will be lost in the world’s ocean in the immediate future, the aviation community finally appears to agree that something needs to be done.
“People are getting really very sensitive to this and they are asking how is it possible that you can track someone’s cell phone but not an airliner in the middle of the ocean,” Cermack concluded.