INTERNATIONAL FEDERATION OF AIR TRAFFIC CONTROLLERS’ ASSOCIATIONS 48th ANNUAL CONFERENCE - Dubrovnik, 20th to 24th April 2009 Agenda Item: B.5.8 IFATCA 09 WP No. 90 Datalink - Review Policy on Downstream Clearances Presented by TOC Summary With Downstream Clearances, a pilot can contact via data link a second controller further down his route and receive a clearance. This service is currently used by pilots to request oceanic clearances before entering North Atlantic airspace. This paper will review the IFATCA Policy on the use of Downstream Clearances considering their current implementation for oceanic clearance delivery according to the safeguards contained in the ICAO Manual of ATS Data Link Applications. A Policy update is recommended in this working paper. 1. Introduction 1.1 Downstream clearances are a specific additional data link that allows the pilots to exchange data link messages with more than one Air Traffic Services (ATS) unit. In 1997 IFATCA adopted Policy on downstream clearances to highlight the necessary safeguards that must be used for any implementation. These safeguards can be found in the ICAO Doc 9694 Manual of Air Traffic Services Data Link Applications. 1.2 The aim of this working paper is to review IFATCA Policy in the light of recent downstream clearances implementations, and other developments. 2. Discussion 2.1 Data link downstream clearances 2.1.1 Downstream Clearance (DSC) is a data link service included in the Controller-Pilot Data Link Communications (CPDLC) application. CPDLC is the electronic dialogue part of the data link implementations (besides surveillance through automatic position reports), allowing controllers and pilots to compose, send and receive text messages on ground and cockpit interfaces such as the Aircraft Communication Addressing and Reporting System (ACARS) instead of voice messages. 2.1.2 DSC is the CPDLC service that allows the pilot to request and receive an electronic clearance from a distant control unit further down along his route via a second data link, while maintaining the initial data link with the current control unit. 2.1.3 DSC is a controversial service since it allows the pilot to receive two clearances from two different controllers with a possibility that each controller does not know what the other controller is sending to the pilot. This service has not been implemented so far, except in the North Atlantic (NAT) oceanic domain to improve the transmission of B.5.8 / Page 1 of 11 oceanic clearances replacing the traditional voice request with an electronic text clearance. 2.2 Oceanic clearances voice procedure 2.2.1 Delivering oceanic clearances via voice is time and frequency consuming. To enter NAT oceanic airspace, an oceanic clearance is mandatory and must be requested from oceanic control at least 40 minutes before entering oceanic airspace. 2.2.2 Below an example of radio communications for the voice procedure between Shanwick Radio and a pilot requesting an oceanic clearance on the second radio (while remaining in contact with domestic control on the primary radio). PILOT: "Good day Shanwick, Speedbird 123 request oceanic clearance". Shanwick: "Speedbird 123, Good day, go ahead". PILOT: "Speedbird 123 request NAT CHARLIE via 53/15 53/20 54/30 54/40 53/50 HECKK SAINT ANTHONY at Flight Level 350 and Mach .80. Estimating 53/15 at 1943 ZULU". Shanwick: "Speedbird 123, Cleared as filed along NAT CHARLIE to BOSTON at FL350 Mach decimal 80 cross 53/15 not before 1940 ZULU". PILOT: "Speedbird 123 cleared track Charlie FL350 Mach decimal 80 53/15 not before 1940 ZULU". Shanwick: "Speedbird 123 correct continue with domestic, bye bye". PILOT: "Speedbird 123, bye". 2.2.3 The drawbacks of this voice procedure are the need for the pilot to use his second radio set while maintaining radio contact on the first set with domestic control. Besides, the oceanic controller has to answer as soon as possible and start a time consuming communication. 2.3 Oceanic clearances DSC potential 2.3.1 The benefits of a DSC oceanic clearance transmitted in text format are obvious: • The pilots maintain only one radio contact (with domestic control) and do not need to contact oceanic control unless the DSC procedure fails or a voice negotiation is necessary. • Upon reception of the DSC request, the oceanic controller has some time to prepare the answer. • The oceanic clearance message elements are unambiguously transmitted and avoid tedious vocal requests and read-backs. • The frequency occupancy is greatly reduced. 2.4 DSC implementations 2.4.1 Gander 2.4.1.1 The Gander Area Control Centre (ACC), located in Gander, Canada, provides air traffic control services over both domestic and oceanic airspace. Picture 1 represents (on the left) “CZQX Domestic” airspace and (in blue) the Gander Oceanic Control Area (OCA). B.5.8 / Page 2 of 11 Picture 1 – Gander oceanic airspace 2.4.1.2 Controllers use the Gander Automated Air Traffic System (GAATS) display: • in domestic airspace with radar and VHF frequencies. • In oceanic airspace, Future Air Navigation Services (FANS) is an ACARS-based onboard data link technology that offers Automatic Dependant Surveillance – Contract (ADS-C) and Controller Pilot Data Link Communications (CPDLC) Radio communications are either VHF close to the continent (“clearance” frequency, for instance) or HF over the ocean through flight service stations operators (“Gander Radio” HF frequencies) that collect and relay the voice communications between pilots and controllers. 2.4.1.3 Data link Oceanic Clearance Delivery (OCD) service is provided via digital VHF and satellite to ACARS equipped aircraft via network service providers ARINC and SITA since 1991. 2.4.1.4 The pilot sends a clearance request (Request oceanic Clearance (RCL)) to Gander ACC when the flight is between 90 and 30 minutes away from the oceanic entry point (or 10 minutes prior to start-up if he is departing from an airport less than 45 minutes away from the oceanic entry point). The RCL includes the same information elements as in a voice request. 2.4.1.5 Within 5 minutes, the ground system verifies that it corresponds to an existing flight plan and acknowledges the reception of the request with a datalink message indicating: “if no clearance received within 30 minutes of oceanic entry point revert to voice procedures end of message” (and if this acknowledgement is not received within 5 minutes, the crew should obviously request the clearance via voice). B.5.8 / Page 3 of 11 2.4.1.6 The oceanic clearance process between Gander domestic and Gander oceanic is completely electronic: the oceanic controller receives an electronic estimate from the domestic (containing the requested flight level, Mach number and route). Based on this information, the oceanic controller develops an oceanic clearance and enters it in the GAATS which sends it electronically to the domestic controller. If a reroute has to be issued for an aircraft for the oceanic entry point, manual coordination is done along with the same electronic process. Picture 2 gives an example of a data link oceanic clearance. Picture 2 –example of data link oceanic clearance 2.4.1.7 The flight level contained in the data link oceanic clearance is the “cleared oceanic flight level” (used in case of lost communications procedures) and the aircraft is supposed to reach this level before entering the oceanic area. The current Gander domestic controller has access to the oceanic clearance and is responsible for providing a clearance to reach this level. 2.4.1.8 When the oceanic clearance is received and possibly printed, the pilot sends a Clearance Acknowledgement (CLA) containing a complete read-back of the elements (he can also be requested in a remark field to read back the clearance via voice). This read-back is checked by the ground system against the issued clearance to uplink a confirmation or cancellation message. 2.4.1.9 Pilots can request an amendment to the oceanic clearance via voice within 200 NM of a Gander clearance delivery frequency station. To amend a clearance, the controller adds a line mentioning “reclearance n°[1 to 9]” and this amendment number is used for acknowledgement. Pilots must also revise via voice their oceanic entry point time by voice if the time deviation exceeds 3 minutes. B.5.8 / Page 4 of 11 2.4.1.10 Various error messages are available in case of service unavailability, early or late request, format error, invalid callsign or flightplan, acknowledgement not received. 2.4.2 Shanwick 2.4.2.1 The Prestwick (UK) Oceanic Area Control Center (OACC) provides ATS within the Shanwick OCA. The Shanwick Automated Air Traffic System (SAATS) is very similar to Gander GAATS and uses the same ADS-C tracks and CPDLC dialogues. HF communications are provided by Shannon (Ireland) Ballygirreen Radio Station (“Shanwick Radio” callsign) operating 20 HF frequency channels. Picture 3 – Shanwick oceanic airspace 2.4.2.2 Shanwick offers the Oceanic Route Clearance Authorisation (ORCA) service to westbound aircraft equipped with ACARS. Clearance request, transmission and acknowledgement are very similar to Gander OCD, including the procedures to revert to voice in case of negotiation request, the revision number included in the clearance text. 2.4.2.3 Picture 4 summarizes the OCD procedure. It represents on the left the satellite or digital VHF networks used by SITA and ARINC to deliver Shanwick ORCA clearances, and on the right the Ground Station relaying the radio communications that are required each time a clearance is not received or acknowledged. B.5.8 / Page 5 of 11 Picture 4 – OCD architecture 2.4.3 Santa Maria 2.4.3.1 Operational trials of OCD in the Santa Maria (Portugal) OCA have started in September 2007. Clearance requests, read-backs and revisions follow the same procedures as in Gander and Shanwick.