Before data analysis by UK satellite operator Inmarsat proved the last contact with the doomed MH370 plane was made from the middle of the southern Indian Ocean, some suggested the aircraft might actually have landed. Why? It's Emergency Locator Transmitter designed to activate in a crash did not send any message.
The absence of this 'SOS call' through the international satellite-based COSPAS SARSAT search and rescue programme has made the hunt for the missing plane extremely complicated.
“These beacons can be triggered either manually, or upon impact or when they come into contact with water,” says Milan Cermack, CEO of Swiss company Applied Space Technology and adjunct professor at the International Space University in France and Memorial University in Canada.
“These beacons are equipped with their own batteries and shouldn’t be affected by any sort of power failure in the aircraft. However, once they sink completely, the water blocks the signal transmission. There were cases in the past when a helicopter or an airplane simply sank like a stone and the beacon didn’t have a chance to activate,” says Cermack, who has extensive experience with search and rescue operations
A possible solution would be to design the beacon to detach from the sinking wreckage and remain floating on the water surface. This way, it could continue transmitting the emergency signal, helping the rescue teams locate the crash site. Although such systems are technically feasible, until the MA370 disappearance there was no push in the aviation community to implement such solutions in commercial airliners.
Beacons not always mandatory
Moreover, there are no set international regulations requiring all aircraft worldwide to be equipped with such a beacon, or Emergency Locator Transmitter. The guidance is fully in the hands of aviation authorities of individual countries.
According to the spokesman of Boeing UK, the lost Malaysian aircraft, a Boeing 777-2H6ER was delivered to Malaysia Airlines with four emergency locator transmitters back in 2002.
However, the company doesn’t have any information about whether the operator (Malaysia Airlines) made any upgrades to the system since.
The COSPAS SARSAT programme launched in 1979 uses SARR (Search and Rescue Repeater) instruments aboard six geosynchronous and five low-earth polar orbit satellites. Until 2009, it was capable to intercept emergency signals send by beacons using the 121.5MHz and 406MHz frequency.
Though the 121.5MHz, a standard air-traffic distress communication frequency, can still be used for close-range homing by search aircraft, COSPAS SARSAT ceased monitoring this frequency in 2009.
The newest version of the 406MHz ELT beacon is capable of transmitting the GPS coordinates, thus enabling much faster localisation with 100m accuracy by both - the geosynchronous and low-earth-orbit satellites. Nowadays, a 406MHz beacon that also transmits the user’s identity and additional homing signal at the 121.5MHz frequency is the "gold standard" in search and rescue.
The non-GPS enabled transmitters can still be tracked down using the Doppler principle that calculates the position towards at least two passes of low-earth orbit satellites within the sight of the beacon. “This procedure entails inherent delays, depending on the position of the beacon on the Earth’s surface, usually in order of several tens of minutes,” explains Cermack.
It is not known which version of the Emergency Locator Transmitter was aboard flight MH370.
Option of last resort
However, for most commercial airliners, the beacon might seem nearly superfluous. Planes don’t actually crash that often and the modern cockpit is equipped with plenty of alternate communication technologies that enable the pilots to send real-time messages if anything goes wrong. However, these systems do require the aircraft’s electrical circuits, including emergency back-ups, to be running.
“Under normal circumstances when an aircraft travels from A to B, the pilots can communicate with air traffic control through VHF radio. However, the VHF range is rather short, up to few hundred kilometres at best,” explains Cermack.
Above oceans and other remote areas, the aircraft still has the ability to stay in touch using various satellite systems.
The Aircraft Communications and Reporting System (ACARS), reportedly disabled aboard the lost aircraft, also sends and receives short messages pertaining to the aircraft status via satellite links.
Cermack explains: “Today, most aircraft would have a satellite phone installed aboard that could be used in the case of emergency – of course, only if the powering electrical systems are operational and the pilots conscious.”
“There are three satellite constellations that can be used: Inmarsat, Iridium and Thuraya. All of them have coverage in the area where the lost MH370 flight was travelling.”
What if the electrical systems went down and the pilots were, for whatever reason, incapacitated? This theory has been put forward by several authors. Retired flight safety manager of the European Space Agency Tommaso Sgobba speculated in an article in Space Safety Magazine about a possible loss of cabin pressure that would lead to the crew first getting 'high' before eventually slipping into unconsciousness and dying due to hypoxia. It would not be the first case such a ghost plane has flown on its own for a long period on autopilot before running out of fuel and crashing.
Canadian pilot Chris Goodfellow, in a Google+ post, has described another scenario that could possibly lead to a similar outcome: a sudden onboard fire disabling electrical systems and producing toxic fumes. In his outline, the pilots might have tried turning the aircraft towards the nearest suitable airport at the Pulau Langkawi island for emergency landing, but were overcome by the smoke, with the plane again continuing until the fire damage rendered it inoperable.
“In this case, the only option left would be the Emergency Locator Transmitter,” says Cermack. “It most likely wouldn’t help save the passengers, but at least it would help narrow down the area where to search for the wreckage.”
Black box countdown
With all communication channels down maybe hours before the actual crash and with the Emergency Locator Transmitter malfunctioning, the search for the wreckage in the Indian Ocean is like looking for a needle in a haystack.
More than two weeks after the plane’s disappearance, all that matters to the investigators now - aside from giving a final resolution to the relatives of the missing passengers - is to find the Flight Data Recorders (FDR), better known as the black boxes.
The FDRs store flight profile information together with all relevant aircraft technical data. They also record communication between the pilots in the cockpit and with the Air Traffic Control. If recovered, they would provide the investigators with a key to understand what really happened during the night flight on March 8.
The black boxes transmit an acoustical signal, usually at 10 to 40kHz that - unlike the radiofrequency transmission from an ELT - can propagate in water. It can be picked up at a distance of 10-15 kilometres - not much considering the sheer size of the search area, which has spanned more than eight million square kilometres
Compounding these issues is the fact that the rescue teams have only 30 days to locate the black boxes, as their batteries rarely last longer.
Read our series of Flight MH370 infographics, documenting the search operation so far