Eyes on the sky: aircraft tracking after MH370

Jun 02, 2015

Over the next 18 months UN body the ICAO wants airlines to implement systems that can fix their flights’ positions every 15 minutes. More onerous standards – requiring near real-time surveillance, tamper-proof systems and military-style ejectable flight recorders – could follow. Alex Derber considers the events behind these developments, and investigates the industry’s readiness meet new tracking proposals.

The vanishing of Malaysia Airlines flight MH370 is probably the most mysterious accident in aviation history and, if more facts are not revealed, could remain so for the foreseeable future. It is not the first commercial aircraft to disappear for so long, but it is the first to do so in the era of satellite communications, while a repeat of the extended, fruitless search for wreckage could be rendered almost impossible by new rules.

Accident investigators, media and conspiracy advocates have pored over the facts of the case. Nonetheless, they bear repeating here as they demonstrate both the extensiveness of current aircraft tracking systems and their limitations.

At 0041 local time on March 8, 2014, a Malaysia Airlines 777-200ER took off from Kuala Lumpur en route to Beijing. About 40 minutes later air traffic controllers had their final voice contact with the aircraft as it transitioned from Malaysian to Vietnamese airspace over the South China Sea. Shortly thereafter MH370 disappeared from secondary radar screens and then, an hour into the flight, a routine update from the 777’s ACARS avionics failed to materialise. An hour and 40 minutes after take-off a Malaysian military radar tracked MH370 over the Andaman Sea, meaning the aircraft had flown almost directly east, re-crossing the Malay peninsula, after its ATC contact an hour before. The flight should have been heading north towards Vietnam.

The military’s primary radar contact was the last definite fix on MH370’s position. Thereafter the only interaction with the aircraft was a regular automated electronic ‘handshake’ between its satellite communications (SATCOM) system and British company Inmarsat’s network of ground satellites. The last such transmission was received almost eight hours into the flight, but from 0915 Malaysian time the aircraft did not respond to pings from ground stations. Although the previous handshakes did not include position information, frequency analysis of the pings enabled investigators to predict that MH370 tracked south shortly after the final radar contact, and ended up in the southern Indian Ocean roughly 2,000 miles off Australia’s west coast. But despite extensive underwater and surface searches, in which 24,000sq-km of sea floor have been scanned, nothing has been found. The Australian Transport Safety Bureau, which is leading the search, expects to have examined all of MH370’s probable landing area by May 2015.

The response

Although MH370 is commonly credited with galvanising efforts to improve aircraft tracking, the ICAO had been considering proposals since the crash of Air France Flight 447 in the Atlantic north-west of Brazil in June 2009. In that case wreckage was located fairly promptly, but it took another two years and roughly $160m to recover of the aircraft’s flight data recorders, or ‘black boxes’, without which the cause of the accident could only be guessed at.

In fact, the recovery of the black boxes was a minor miracle: Between AF447 in 2009 and May 2014 10 flight recorders from 11 accidents over water were not found. To remedy this there have been several proposals to improve the location of flight recorders or access the data they contain. Thus from 2018 the battery life of underwater locator beacons (ULBs) on the cockpit and flight data recorders must rise from 30 to 90 days, while large aircraft should include a third, long-range underwater locator attached to the airframe.

France’s BEA agency, which led the search for AF447, concluded that aircraft manufactured after 2020 “should have the capability to either automatically transmit positional information or an emergency locator signal prior to an accident occurring, or be fitted with a deployable emergency locator transmitter (ELT) in order that an accident site for an aeroplane can be established within a 6NM radius”.

Of the two options, industry and the ICAO is leaning towards automatic position reporting, a performance-based measure that shouldn’t initially require new equipment being installed on aircraft. Thus the ICAO’s High Level Safety Conference recently recommended that aircraft outside radar range of air navigation service providers (ANSPs) – which usually means over oceans – transmit position data every 15 minutes.

Most widebody aircraft flying today contain the hardware necessary to comply with the above requirement. MH370, for instance, had the capability to transmit oceanic position data via its satellite systems, but this was not activated due to the flight’s intended route across neighbouring ANSPs, which normally track aircraft via secondary radars that pick up ADS-B radio signals. These provide more extensive position data than those received by primary radars, but obviously need the ADS-B transponders on the aircraft to be switched on and functioning.

Outside the reach of primary and secondary radars, aircraft can be tracked with ADS-C, which was launched in the 1990s to replace the high-frequency voice communications that flight crew used to report their position when operating far out over water.

“ADS-C was designed to provide reports at the same rate required by ATC for voice reports down to about once every 15 minutes, but it can send the data more often,” comments Philip Clinch, vice-president of AIRCOM services at SITA. His company’s AIRCOM Flight Tracker is a ground-based software system that enables operators to determine the position of an aircraft at any time in any location. It requires no modification to aircraft and operates as an extra layer on top of SITA’s existing AIRCOM Server ACARS message handling system, which 80 airlines are already using around the world.

Flight Tracker is a response to a shift in responsibility when it comes to aircraft tracking. Instead of leaving the task mainly to ANSPs, the ICAO is now asking airlines to take responsibility for tracking their aircraft and identify any problems in near real-time. SITA’s system gathers data from multiple sources before integrating them into a single application with the best available position information.

“The change introduced by the SITA Flight Tracker is to give the airlines an ATC-like system that will allow the airlines to start making direct use of the FANS avionics,” explains Clinch. Previously, FANS was only used by ATC for surveillance and safety purposes.

Inmarsat helps provide 4D position data – which encompasses an aircraft’s heading, position, altitude and speed – using ADS-C over areas where other sources of surveillance are not available. Its Classic Aero service is used by the vast majority of widebody operators and allows FANS (Future Air Navigation System), ACARS (Aircraft Communications Addressing and Reporting System) and ATN (Aeronautical Telecommunications Network) avionics to communicate via data-link over the company’s constellation of Inmarsat-3 and Inmarsat-4 satellites.

The company is also investing $1.6bn in Global Xpress and SwiftBroadband Safety – enhancements to its network that should become operational in 2016. “This will enable additional aircraft and cockpit services, such as enhanced weather and turbulence reporting, and support near real-time, enhanced aircraft position reporting and tracking using frequent ADS-C position reporting,” says Mary McMillan, VP safety and operational services at Inmarsat.

Autonomous reporting

As of early 2015, there are no regulations governing how aircraft should be tracked outside primary or secondary radar coverage. ICAO members hope to have adopted the 15-minute reporting requirement before the end of the year. Their aim is that airlines – not manufacturers or ANSPs – would be responsible for compliance with the new rule by November 2016. As shown above, compliance is possible with existing technology.

“Under certain circumstances, the 15-minute service is already being used in oceanic flight information regions. The frequency of the position report is determined based on the separation standard being applied,” notes McMillan.

However, a longer-term and more ambitious plan is outlined in the ICAO’s Global Aeronautical Distress & Safety System (GADSS) proposal. This defines three flight states – normal, abnormal and distress – and appropriate responses to each.

In normal flight the incoming standard requires aircraft positions to be updated every 15 minutes. Subsequent regulations plan to increase this to every minute if an abnormal event occurs, with activation occurring either automatically, or manually by air or ground crew. Furthermore, the one-minute transmission should only be halted in the same manner it was initiated, in order to prevent maliscious or mistaken human interference, from the ground or air, with a tracking system.

The big difference between the 15- and one-minute transmissions occurs when aircraft enter the distress phase. Then, an autonomous system should kick in and start relaying the one-minute signal. This means that an aircraft in distress should be able to broadcast 4D data independently of its power and avionics systems. Clinch at SITA comments that “to quickly activate emergency tracking will require avionics changes to detect abnormal situations”. Presumably, airlines would need to retrofit hardware capable of this.

At Inmarsat, however, McMillan says that flight tracking through existing FANS ADS-C can cover normal, abnormal and distress conditions: “Importantly, ADS-C has in-built conformance monitoring that automatically alerts air traffic control personnel to any unauthorised altitude change or flight track deviation. The alerting and flight change reporting rates are conditions set up in the contract [between the airline and ANSP] and are managed independent of the flight crew.”  

Flight recorders and ELTs

One concept that would undoubtedly impose an extra cost is the deployable flight recorder – an extra flight recorder attached to the exterior of the airframe – usually in the tail – that separates on impact with the ground or water, or in a mid-air collision or explosion. Its aim would be to record the maximum amount of flight data before a crash. The device would incorporate its own emergency locator transmitter (ELT) and should be able to land intact away from the main wreckage of the aircraft.

Airbus is currently in talks with European regulator EASA about installing ejectable flight recorders on its A350 and A380 aircraft, and is considering doing the same for the A330 and A320. Boeing, however, fears that the technology could pose safety problems through accidental deployment and is not planning to install additional recorders.

Standalone ELTs also help search and rescue teams find aircraft and life rafts, and the ICAO mandates that aircraft carry at least one of these, although it also notes that “detection of ELT signals after an aircraft crash remains problematic”. Problems have included malfunctions of the beacon triggering system, disconnection of the beacon from its antenna or destruction of the beacon in a crash or explosion.

According to Boeing, “It is important that global standards be performance-based rather than based on prescribed technical solutions so that, as technology evolves, so too can solutions. As a means for quickly locating an aircraft, global tracking provides an alternative means of compliance for the automatic emergency locator transmitter.”

The ICAO, meanwhile, told ATE&M that the planned autonomous distress tracking rule “circumvents the need for proposals like a second ELT being put onto an aircraft, so it’s seen as an impetus for early adoption”.

Ground stations

Aerial communications equipment on satellites and aircraft is only half the story. The majority of flights, particularly those operated by narrowbodies, fly inside the coverage of air navigation service providers (ANSPs), also referred to as air traffic control (ATC).

Within range of ground stations, aircraft can transmit data and voice signals via their VHF and HF radio antennas. Like SATCOM systems these allow anything from flight crew discussions with ATC, to position reports, to automated maintenance messages, to be sent.

They are also tracked by ANSPs’ secondary radars, which interrogate ADS-B transponders to receive an aircraft’s 4D data and expected position in the near future based on the flight computer. Ground stations relay the data to ATC centres, where it is combined with primary radar coverage to paint a detailed picture on controllers’ screens. Aircraft equipped with ‘ADS-B In’ can also see other aircraft positions in the sky around them.

The tracking capabilities of ADS-B make it a vital tool in reducing separation in crowded skies and improving traffic management. The FAA’s NextGen ATC plan mandates that all aircraft over the United States are equipped with ‘ADS-B Out’ by 2020, while EASA has stipulated that all users of European airspace must incorporate the same technology by December 2017. About two-thirds of commercial aircraft are currently equipped with ADS-B transponders.

But ground-based ADS-B receivers cluster around high-traffic areas, meaning that only about 10 per cent of the world is covered by them and primary radar. To remedy this Virginia-based Aireon is installing ADS-B receivers on the satellites of its parent company, Iridium, which could potentially provide global ADS-B coverage from 2018.

Trickling along the tracking timeline

MH370 provoked public outrage as well as disbelief that a large commercial aircraft, packed with communications equipment, could evade detection not just in the year following its disappearance, but also for almost nine hours after the pilots last checked in with Malaysian ATC. During that time the flight would have passed through or very close to Malaysian, Vietnamese, Thai and Indonesian airspace, yet a solitary military radar contact was the only trace it left.

From 2016 it is expected that airlines should know their flights’ positions every 15 minutes, but the ICAO’s proposals do not stipulate tamper-proof systems. MH370’s ADS-B transponder either stopped working or was deliberately deactivated. The autonomous one-minute position update – which kicks in if other tracking systems fail and allows aircraft to be located within six nautical miles of the last signal – will only apply as an ICAO standard by 2021 at the earliest. Deployable flight recorders would only be demanded by the same date, if, indeed, that proposal is ever adopted.

And although most widebody aircraft contain the technology to comply with the 15-minute standard, some airlines have balked at the ICAO’s probable 2016 deadline for that tracking standard. Airline body IATA reportedly deemed the timescale impractical. Of course, individual aviation regulators, such as the FAA and EASA can and probably will impose their own rules. In 2015, for instance, Airservices Australia became the first ANSP to trial the ICAO’s initial standard, meaning that all commercial aircraft fitted with ADS-C are tracked every 15 minutes within Australian airspace.

As stated above, though, the ICAO wants airlines as well as ATC providers to know where their aircraft are. Air France and Malaysia Airlines both now have forms of internal oversight in place – the challenge will be to convince other operators before disaster strikes.