Staying on Track

On March 8, 2014, a modern commercial airliner disappeared from the skies and, after an extensive international search, investigators have verified that recently-found debris is indeed from that flight. Theories abound, yet no one can prove what happened to Malaysia Airlines Flight 370 (MH370).

Five years before, the Air France Flight 447 (AF447) accident had already highlighted vulnerabilities in the air navigation system. These deficiencies hindered the timely identification of an aircraft experiencing a “distress” event and the subsequent search and rescue efforts, notes a draft version of ICAO’s Global Aeronautical Distress & Safety System (GADSS) Concept of Operations (ConOps) document.

In the aftermath of the tragic circumstances of MH370, the International Air Transport Association (IATA) formed the Aircraft Tracking Task Force (ATTF). From May until September 2014, experts worked together with the purpose of assessing and improving the current state of global aircraft tracking capabilities. 

“Most airlines track their aircraft through a variety of methods described in the ATTF report,” explained Rob Eagles, IATA’s interim senior vice president, safety and flight operations. “The vast majority of those airlines that track their aircraft do so through air traffic surveillance services, where such services exist. The ATTF report is not an exhaustive study. No regional differences in tracking were identified, nor is it possible to say on the basis of the report that any such differences exist. The ATTF also verified that there are existing technologies, services, and procedures that can enhance aircraft tracking in the near-term.” 

While IATA’s task force was at work, the International Civil Aviation Organization (ICAO) was also examining the possibilities presented by new flight tracking standards. “[This] work….resulted in the concept of operations for a new Global Aeronautical Distress and Safety System (GADSS),” said Anthony Philbin, chief of communications at ICAO.

The analytical work performed by both IATA and ICAO to improve aircraft-tracking capabilities resulted in ICAO issuing performance-based requirements for the seamless transmission of position data from an aircraft at least every 15 minutes. 

If an abnormal event posing a flight risk and requiring immediate crew action is detected, the aircraft position data is transmitted about once per minute. An increased reporting rate may lead to communication between the aircraft operator and an air traffic service unit (ATSU), and subsequently to an emergency phase, reports ICAO in the GADSS ConOps document.

The definition of performance-based requirements for aircraft tracking allows valuable flexibility to service providers who need to upgrade their tracking capabilities. Performance-based requirements define general safety objectives that may be met by service providers through a variety of means, so long as the safety objectives are achieved. 

“Where appropriate, ICAO has been pursuing performance-based standards and recommended practices (SARPs) for some time now, and not only with respect to aircraft tracking,” commented Philbin. “This is mainly because they permit States and operators greater flexibility in terms of the solutions and investments required to meet the associated requirements. Prescriptive standards can also have the negative side effect of stifling further innovation; for instance, where a specific technology solution may become internationally mandated but is subsequently made out-dated by new discoveries or developments. Performance-based standards permit States and industry to take advantage of the most technically- and cost-effective solutions present at any given time.”

The adoption of a performance-based approach for aircraft tracking standards is praised by IATA: “Performance-based standards allow airlines to choose the best option for their aircraft and operations,” noted Eagles. “Airline operations are diverse and not all airlines use the same type of equipment. Not all air navigation service providers enjoy the same capabilities. There is no ‘one size fits all’ solution. There are existing technologies, services, and procedures that can enhance aircraft tracking in the near-term. Established procedures must be followed and improved where needed to ensure clear, consistent, and timely communications between air navigation service providers and airlines.”

He added that prescriptive standards could “lock” the industry into systems and technology that may soon be superseded by superior solutions. For example, the availability of space-based ADS-B, which is expected in a few years, will address the tracking issues raised by the disappearance of MH370. “Additionally, the disappearance of MH370 has highlighted the importance of ensuring adherence to the existing clearly defined roles and responsibilities of air navigation service providers and airlines,” concluded Eagles.

On top of defining the requirements, ICAO has also started the process leading to their implementation. Both the 15-minute foundational requirement and the one-minute distress tracking requirement underwent a preliminary review by ICAO’s air navigation commission in January 2015, and by May 2015 both state letters were issued. The foundational requirement will be adopted in November 2015 and is expected to become applicable as of November 2016; similarly, the distress requirement will become applicable in November 2016 to become operational in January 2021, according to Philbin.

Airliners are under air traffic control/air traffic services (ATC/ATS) throughout all phases of flight. ATC/ATS includes secondary surveillance radar (SSR), multi-lateration, and ground-based automatic dependent surveillance-broadcast (ADS-B). Because surveillance services provide the location and identification of an aircraft in order to manage separation, this information can also serve as a form of aircraft tracking. In fact, a large number of commercial aircraft operators currently use ATS surveillance services to track their aircraft, particularly in medium to high density airspace. Surveillance services can be disrupted, however, due to planned or unplanned maintenance issues or equipment availability. For ground-based radars that provide surveillance services, there can be permanent or periodic line of sight limitations due to obstructions and the curvature of the earth, notes the ATTF report.

ADS-B is a means by which aircraft can automatically transmit and/or receive data such as identification, position and additional information, as appropriate, in a broadcast mode via a data link. ADS-B technology—both ground- and space-based—is likely to provide significant benefits in aircraft tracking, both in high and low density airspace. The expansion of space- and ground- based infrastructure to achieve global coverage during all phases of flight is, however, an area for improvement, according to ICAO. 

“The ADS-B ground infrastructure is not complete enough to provide adequate global tracking capability. Space-based ADS-B is not yet available. Geostationary satellite systems tend to have incomplete coverage of the globe,” reads the GADSS ConOps document.

“Space-based ADS-B is expected to have a significant impact on global ATS surveillance services and thus on global aircraft tracking capability. Space-based ADS-B will use signals from Mode-S transponders which are already installed or planned to be installed on most commercial aircraft. Space-based ADS-B should be available in 2018,” reports the ATTF. “In addition to the launch of satellites, frequency allocation is a critical element to making this capability a reality. At present, the 1090 MHz band is allocated to the Aeronautical Radio Navigation Service. For satellites to receive aircraft transmitted ADS-B signals, as required for at least one space-based ADS-B concept, the band would also need to be designated for the Aeronautical Mobile Satellite Route Service by the International Telecommunications Union. Efforts are underway to obtain this designation.”

In remote or oceanic low density airspace, aircraft location and identification information is instead often provided by periodic position reports and voice communications between the flight crew and the air navigation service provider (ANSP). Based on a limited survey of airline tracking practices, fleets are tracked through operations control centres (OCCs) using aircraft communications addressing and reporting systems (ACARS), which transmit short messages between the aircraft and ground stations via VHF/HF radio or satellite communications. There are areas of the world where aircraft tracking capabilities are limited by lack of communications infrastructure, interference issues, or other factors that impact use of technology, notes the ATTF report.

With regard to the reliance on VHF/HF as the sole means of communication over remote and oceanic areas, ICAO affirms that, “Aircraft in remote and oceanic areas are frequently the subject of emergency phases due to loss of HF communications. Associated human complacency issues may lead to delayed SAR (search and rescue) response to a genuine emergency (e.g. AF447). Carriage of satellite communications equipment as a secondary means to HF will assist to confirm the safety of an aircraft, or otherwise.”

In some low density airspace, automatic dependent surveillance – contract (ADS-C) is used to obtain position reports, notes the report of the ATTF; however, aircraft operators are not using ADS-C capability to the degree possible, affirms ICAO. ADS-C is the means by which the terms of a reporting plan establishing the conditions of data reporting are exchanged between a ground system and the aircraft, via a data link, specifying under what conditions ADS-C reports are initiated, and what data is to be contained in the reports. ADS-C position reports are automatic position reports made to an ATS unit in the form of a data block. The requirements for the transmission and contents of ADS-C reports are established by the controlling ATS unit on the basis of current operational conditions and communicated to the aircraft and acknowledged through an ADS-C agreement.

A substantial percentage of the current wide-body fleet of aircraft is equipped and capable of transmitting automatic dependent surveillance–contract (ADS-C) positions using FANS 1/A datalink, an avionics system which provides direct data link communication between the pilot and ATC, including air traffic control clearances, pilot requests, and position reporting. FANS 1/A is a range of future air navigation systems (FANS) products; FANS-1 refers to the Boeing solution; and FANS-A is the Airbus solution. While it may be implemented also through an ANSP, ADS-C provides a near-term capability for aircraft tracking where ATS surveillance systems are not available, as well as the potential for global coverage. Limitations of ADS-C are represented by the investment required to support OCC functionality, additional data transmission cost, installation costs and geographical limitations due to satellite footprint, according to the ATTF report.

Estimating the investment needed to implement aircraft tracking solutions, both in financial and organizational terms, is a difficult exercise. According to the U.S. Government Accountability Office (GAO) report 14-443, airlines that currently do not meet the identified aircraft tracking performance standards would face some costs. Estimates of those costs across the fleet are difficult to determine with any precision because data on the level of aircraft equipage are not consistently available. As well, the contracts between the airlines, avionics manufacturers, and air transport communications service providers to provide such services are proprietary.

“The ATTF did not attempt to determine investment required. Furthermore, we are not aware of cost or organizational estimates with regard to implementing the proposed ICAO tracking standard. However, the immediate focus should remain on leveraging equipment already installed on aircraft,” said IATA’s Eagles.

According to the GAO report, costs to equip with ACARS using VHF radio could be up to $100,000 per aircraft. Additionally, ACARS using satellite communications would cost another $60,000 to $150,000 per aircraft for Iridium or Inmarsat equipment, according to one air transport communications service provider. However, most long-haul aircraft that fly in oceanic and remote regions are already equipped with those units. For aircraft without FANS, there would be an additional cost of up to $250,000 for a new FANS-capable flight management system.

The GAO additionally highlights that, “In order to more frequently report position information using ACARS or FANS, airlines may have to pay for increased data transmission, but we were unable to determine the extent of these costs to industry. According to one air transport communications service provider, ACARS data transmission costs per month can range from $500 per short-haul aircraft using VHF radio systems, to approximately $1,000 per aircraft for long-haul aircraft using satellite communications over oceans. According to one domestic airline, airlines pay for ACARS messages through plans similar to cellular text messaging; and therefore, it is not clear whether more frequent position reports would be covered under existing plans, or would require new plans at a higher cost.”

The GAO also notes that in order to help mitigate costs and enhance tracking capabilities in the near term, some service providers have offered a number of proposals to enhance flight tracking. 

“One proposal offered by the satellite communications provider Inmarsat would provide four free position reports per hour using FANS ADS-C capability. To take advantage of this proposal, aircraft would need to be equipped with FANS and Inmarsat satellite communications. 

A separate proposal from SITA, a major provider of ACARS data, aims to provide ADS-C reports to airlines. According to SITA, the company’s proposal may help improve coordination between the airline and the air navigation service provider, especially if there is an unexpected event on board the aircraft. Rockwell Collins, the other major providers of ACARS data, unveiled a flight tracking service in March 2015 that utilizes several data sources, including ADS-B, ADS-C, and ACARS, reports the GAO.