Limitations in the current air navigation system, which have hampered the timely identification and localisation of aircraft in distress, have been highlighted by tragedies such as the losses of Air France 447 and Malaysia Airlines 370. These limitations significantly hindered both effective search and rescue efforts and the recovery operations. International Civil Aviation Organisation (ICAO) has identified that the current effectiveness of alerting search and rescue services could be enhanced by developing and implementing the Global Aeronautical Distress and Safety System (GADSS).
From a high level perspective, the GADSS is designed to address three specific issues:
- The late notification of SAR services when aircraft are in distress
- Missing or inaccurate end of flight aircraft position information (for example, the location of wreckage in the event of a crash)
- Lengthy and costly retrieval of flight data for accident investigation
The consequent objectives of the GADSS are therefore to:
- Ensure timely detection of aircraft in distress
- Initiate search and rescue (SAR) actions as efficiently and as quickly as is possible
- Ensure tracking of aircraft in distress and provide timely and accurate location of end of flight
- Accurately direct SAR actions
- Enable efficient and effective SAR operations
- Ensure timely retrieval of flight data recorder data
According to the ICAO Concept of Operations, the Global Aeronautical Distress and Safety System (GADSS) will address all phases of flight under all circumstances including distress. This GADSS will maintain an up‐to‐date record of the aircraft progress and, in case of a crash, forced landing or ditching, the location of survivors, the aircraft and recoverable flight data.
The three main functions of the GDASS are:
The GDASS Aircraft Tracking function is planned to provide an automated 4 dimensional position (latitude, longitude, altitude and time) at a reporting interval of 15 minutes or less. This reporting interval will result in a reduction of the time necessary to resolve the status of an aircraft or, when necessary, help to locate an aircraft. If air traffic services obtain an aircraft position at 15 minute intervals or less, it will not be necessary for the operator to track the aircraft. However, should the aircraft be operating within an area where ATS obtains the aircraft position at intervals greater than 15 minutes, the operator will be required to ensure that the aircraft is tracked.
In general terms the aircraft tracking function:
- Does not introduce any change to current ATC alerting procedures
- Establishes operator responsibilities for tracking based on areas of operation
- Is not technology‐specific
- Establishes communication protocols between operator and ATC
Autonomous Distress Tracking
The Autonomous Distress Tracking (ADT) function will be used to identify the location of an aircraft in distress with the aim of establishing the location of an accident site within a 6 NM radius. An aircraft is considered to be in a distress condition when it is in a state that, if the aircraft event is left uncorrected, may result in an accident. Triggering criteria might include items such as unusual attitudes, altitudes or speeds, potential collision with terrain, total loss of thrust on all engines, Mode A squawk codes, and others as defined by the operator.
The ADT function will use on-board systems to broadcast either aircraft position (latitude and longitude), or a distinctive distress signal from which the aircraft position and time can be derived. Once the ADT has been triggered by a distress condition event, the aircraft position information will be transmitted at least once every minute.
Post Flight Localization and Recovery
In the event of an accident, the immediate priority is the rescue of any survivors. The ADT function will greatly reduce the potential search area and even more accurate aircraft position information will be provided through the Post Flight Localization function by means of Emergency Locator Transmitter (ELT) and/or homing signals to guide SAR services on site.
To facilitate the ability to locate the wreckage and recover the flight recorder data after an accident, the post flight localization and recovery function specifies a number of requirements for ELTs, Underwater Locator Beacon (ULB) and flight recorders which are being incorporated into the provisions of ICAO Annex 6.
The operational concept for GADSS implementation revolves around a cooperative relationship between ATS, the aircraft operator and Rescue Coordination Centres (RCC). The first two each have an active role and responsibility for tracking an aircraft in flight and will advise the third in the event that loss of position update is experienced or that ADT is activated. Similarly, if a search and rescue asset detects an emergency signal, such as an ELT from an aircraft, the affected RCC will notify ATC and the operator.
RCC, ATS and the aircraft operator each have specific duties and responsibilities during each of the three defined ICAO Emergency Phases (Uncertainty Phase, Alert Phase and Distress Phase). For complete details of these responsibility relationships, refer to the GADSS Concept of Operations manual listed under Further Reading below.