2.7 FANS 1/A(+) and ATN. Some avionics implementations support both the FANS 1/A(+)-based applications and associated protocols and the ATN-based applications and protocols. Depending on the system used by the ATSU, pilots may be required to logoff/disconnect any existing CPDLC or ADS-C session(s) and reestablish contact to another ground system when seamless transfer is not possible.
2.8 ACARS ATS. ACARS is a digital data link system for transmitting short, relatively simple messages between aircraft and ground stations via VHF, HF, or satellite.
Note: The ACARS network also carries FANS 1/A(+) messages.
2.8.1 Background. ARINC designed the ACARS protocol to replace VHF voice service in 1978. Later, Société International de Télécommunications Aeronautiques (SITA) added additional radio stations to augment this service. Airlines introduced ACARS in the late 1980s to reduce crew workload and improve data integrity. Although the term ACARS is often thought to encompass only a single data link system installed on the aircraft, it actually refers to a complete air and ground system.
2.8.2 Aircraft and Ground ACARS Systems. The aircraft portion of ACARS system consists of an avionics computer called an ACARS management unit (MU) and a control display unit (CDU). On the ground, the ACARS system is made up of a network of radio transceivers to receive (or transmit) data link messages and route them to various airlines on the network.
2.8.3 ACARS ATS Supported Applications Include:
• Departure Clearance (DCL) (not to be confused with CPDLC-DCL),
• Oceanic clearance (OCL),
• Terminal Weather Information for Pilots (TWIP), and
• Digital Automatic Terminal Information Service (D-ATIS).
2.9 Tower Data Link System (TDLS). The TDLS automates tower-generated information for transmission to aircraft via data link communication for both CPDLC-DCL and Pre-Departure Clearance (PDC). The TDLS interfaces with sources of local weather data and flight data in order to provide pilots with PDC, D-ATIS, and CPDLC-DCL services.
Note: The term PDC refers to the U.S. ATS of DCL. The DCL includes flight plan route, climb via, and/or initial/requested altitude, beacon code assignment, and departure frequency.
2.10 CPDLC-DCL. CPDLC-DCL is available at various airports in U.S. domestic airspace using FANS 1/A(+) via VDL Mode 0/A and/or Mode 2 for departure clearance services.
2.10.1 Dispatch or Flight Following Systems. For operators with a dispatch center, flight following system, or other base of operations, copies of all data link 2-5
communications may be routed to, and stored by, the operator. Contact the FAA Data Communications Program Office (refer to their website) to coordinate.
2.10.2 CPDLC-Departure Clearance Service (CPDLC-DCL). CPDLC-DCL provides a means for requesting and delivering initial and revised DCLs. These CPDLC messages include departure procedure, flight plan route, initial and requested altitude, beacon code, departure frequency, and other non-route information.
Note 1: CPDLC-DCL is different than international DCL operations.
International systems use the ACARS ATS DCL application via ARINC 623/European Organization for Civil Aviation Equipment (EUROCAE) ED-85A, not the FANS CPDLC application.
Note 2: At participating airports, PDC services may be available for non-FANS equipped aircraft.
2.10.3 CPDLC Specified on the Airport Diagram. To differentiate what communication services are available at each facility, refer to the airport diagram, Standard Instrument Departures (SID), and other terminal procedures pages. See Figure 2-3, Data Link Communication Services on Departure Procedure, for the CPDLC annotation on a departure procedure.
Figure 2-3. Data Link Communication Services on Departure Procedure (CRSON4.CRSON) 17117 SL-253 (FAA)
CRSON FOUR DEPARTURE (RNAV) MEMPHIS INTL (MEM) MEMPHIS, TENNESSEE D-ATIS 127.75 TOP ALTITUDE: HUMMS CINC DEL 5000
125.2 CPDIC
GND CON
121.0 379.2 (Rwy 9-27)
121.9 379.2 (Rwys 18C-36C, T8t- CRSON
121.65 379.2 (Rwy 18R-36L)
MEMPHIS TOWER
118.3 257.8 (Rwy 9-27)
119.7 257.8 (Rwys 18C-36C, 18L-36R) CPDLC Services Available
128.425 257.8 (Rwy 18R-36L)
MEMPHIS DEP CON
124.15 385.45 TAKEOFF MINIMUMS:
Ruys 9, 18L/C/R, 27, 36L/C/R:
Standard with minimum climb of 500' per NM to 860.
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2.10.3.1 CPDLC-DCL logon/notification (see paragraph 5.3). “KUSA” is the National Single Data Authority (NSDA) for all CPDLC logons/notifications in the United States. Pilots activate the data link communication system anytime during preflight by logging on to/notifying KUSA with ATC. Within 30 minutes of the proposed departure time, an “ATC Connection Established” message will be received if the following conditions are met:
1. Logon/notification information was correctly formatted;
2. An ATC-filed flight plan is on file;
3. Flight plan indicates the aircraft is CPDLC-DCL capable; and
4. ATC controller has approved the DCL.
2.10.3.2 Once a successful ATC connection has been established and the CPDLC-DCL has been approved by the controller, the CPDLC-DCL will be automatically sent to the aircraft. Pilots do not have to request a clearance. After the clearance is received and verified, pilots should:
1. Review the clearance and verify that no clarification from ATC is required (Reject/Unable);
2. Confirm the appropriate runway, if assigned, departure procedure, and transition with no discontinuities; and then
3. Acknowledge (ROGER (DM3)/WILCO (DM0) or UNABLE (DM1)) the message.
Note 1: If it becomes necessary to revert to voice after receiving a clearance, pilots should respond with Reject/Unable to the uplinked clearance.
Note 2: For CPDLC-DCL ground operations only, pilots can expect an automated ATC-initiated logoff/disconnect 5 to 10 minutes after takeoff.
2.10.3.3 If changes in tower or en route conditions occur (e.g. weather) the ATSU may amend the clearance information and transmit a revised CPDLC-DCL. Pilots should follow the same procedure for revised clearances.
2.11 PDC. PDC is a subscriber based service to provide an effective and efficient means of delivering a text-based electronic departure clearance prior to taxi. Data link communication technologies are utilized via a PDC in which ATC clearances are sent to a subscriber’s dispatch center, flight followers, or base of operations. The clearance is made available to the pilot with the following formats:
1. Internet access,
2. Airline gate terminal, 2-7
3. Airline operations area terminal,
4. Fixed-Base Operator (FBO) terminal, and
5. ACARS.
2.11.1 PDC Communication. It is not necessary for an aircraft to be equipped with data link communication avionics for a flight to participate in the PDC service. It is only necessary for the pilot to be able to obtain a printed or electronically displayed copy of the PDC message prior to taxi (may be printed at the FBO terminal, the airline gate, etc.).
The contents of the PDC message are relayed to the aircrew without modification, omission, or alteration. PDC is at the discretion of the clearance delivery controller. If the controller determines that issuing a PDC could introduce confusion, the controller will issue a verbal clearance to the aircrew. If the pilot is uncertain of the clearance, the PDC must not be used and the pilot must contact clearance delivery via voice (telephone or radio) and obtain their clearance.
2.11.2 PDC vs. CPDLC-DCL. The primary difference between the PDC and CPDLC-DCL services is the PDC service depends on the operator or other third party to deliver the PDC to the aircraft whereas CPDLC-DCL service is a direct connection after logon/notification from the tower automation to the flight deck avionics of FANS-equipped aircraft. See Table 2-1, PDC vs. CPCLC-DCL, below for a side-by-side comparison.
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Table 2-1. PDC vs. CPDLC-DCL
PDC CPDLC-DCL No Logon/Notification Required Logon/Notification Required Sent to AOC or other Operator prescribed location Automatically sent directly to FANS 1/A(+) equipped aircraft over data link communication equipment after crew logon/notification Delivered to the pilot by various means (i.e., over ACARS, to the FBO terminal, to the airline gate) Delivered over data link communication directly to the aircraft within 30 minutes of proposed ETD Depending on the delivery method, may require a printed copy to be delivered to the aircraft Never requires a paper copy to be delivered to the aircraft Does not require data link communication equipment to be installed in the aircraft Requires data link communication systems on the aircraft Does not support revised clearances. Revisions must be transmitted via voice frequency Revised clearances can be delivered directly to the aircraft when necessary without restrictions A specific call sign can only be used once in an adaptable time period of 12–18 hours at a specific airport Only one call sign for a given tail can be in use for CPDLC-DCL clearances at any given time Requires manual input by the pilot or may be uploaded from an AOC Clearance can be sent to the avionics system which may enable “push to load” via a load prompt
2.12 Data Authority. “KUSA” is the national data authority for all U.S. domestic CPDLC logons/notifications. Figure 2-12, Data Communication Services Strategy, describes the current and planned data communication services to be available in the domestic en route environment. CPDLC en route operations in U.S. domestic airspace will use FANS 1/A(+) equipped aircraft with multi-frequency VDL Mode 2 radios. For an alternate subnetwork, see paragraph 4.6.2.
2.12.1 Current Data Authority (CDA). When an aircraft system accepts a CPDLC connection, this active connection initiates the exchange of messages between the ATSU and the aircraft as the ATSU becomes the CDA. The CDA typically initiates address forwarding to permit a downstream or adjacent ATSU (next data authority (NDA)) to establish an inactive CPDLC connection and/or an Automatic Dependent Surveillance (ADS) contract for monitoring purposes.
2.12.2 Data Authority Transfer. When the active CPDLC connection is terminated, the aircraft will activate any inactive connection. In this case, the next data authority becomes the CDA and is now able to exchange CPDLC messages with the aircraft. Figure 2-4, Next Data Authority Notification, illustrates the transfer from the CDA to the NDA.
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Figure 2-4. Next Data Authority Notification
2.13 ATSUs and Aircraft Interoperability. Figure 2-5, Air Traffic Service Unit (ATSU) and Aircraft Interoperability Designators, shows different ATSU ground systems and interoperable aircraft systems. The diagram shows the CSP and its Centralized ADS-C System (CADS). CSP’s CADS enables an ATSU without FANS 1/A capability to receive ADS-C reports from any FANS 1/A, FANS 1/A(+) or FANS 1/A ADS-C aircraft.
A designator is assigned to each type of ATSU and aircraft data link system.
Explanations of each interoperability designator are provided below in Table 2-2.
Table 2-3, Types of Data Link Systems and Operations, provides an overview of the operational capabilities that are supported by each of the different data link systems.
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Figure 2-5. Air Traffic Service Unit (ATSU) and Aircraft Interoperability Designators Aircraft with multiple types of data link communication systems
(e.g. FANS 1/A-ATN B1 and ACARS ATS) ATSU in Oceanic ATSU in Any Airspace ATSU Continental and Remote Airspace Airspace - FANS 1/A (Generic) ACARS ATS FANS 1/A FANS 1/A+ B2* ATN B1 FANS 1/A ADS-C *As defined in this AC.
CSP Can interoperate with any B2 ground station.
CADS ATSU - CAD ACARS ATS FANS 1/A+ B2 ATN B1 2-11
Table 2-2. Interoperability Designators and Descriptions Interoperability Designator Description ACARS ATS ATS applications, DCL, OCL, TWIP, and D-ATIS supported by ACARS.
Note: The term DCL used internationally is similar to the term PDC used in the United States.
ATSU CADS CSP’s CADS enables an ATSU without FANS 1/A capability to receive ADS-C reports from any FANS 1/A, FANS 1/A(+) or FANS 1/A ADS-C aircraft.
FANS 1/A Initial FANS 1/A ATSU applications, ATSU Facilities Notifications (AFN), CPDLC, and ADS-C supported by FANS 1/A.
Note: FANS 1/A typically involves communication (CPDLC), navigation (Area Navigation (RNAV)/Required Navigation Performance (RNP)) and surveillance (ADS-C). This document refers to the FANS 1/A for the data link system, which includes the CPDLC and ADS-C applications. Refer to ICAO Doc 9613 for guidance material on navigation (RNAV/RNP) qualification and use.
FANS 1/A ADS-C ATSU applications AFN and ADS-C supported by FANS 1/A.
FANS 1/A ADS-C comply with AFN and ADS-C applications, but do not include CPDLC application.
FANS 1/A+ Same as FANS 1/A, except with additional features, such as the message latency timer function, described in DO-258A/ED-100A.
Note 1: FANS 1/A(+) aircraft is interoperable with FANS 1/A and FANS 1/A(+) ground stations. However, message latency capability is only available when FANS 1/A(+) ground stations interoperates with FANS 1/A(+) aircraft.
Note 2: Seamless transition of ATSU data link service occurs between ATN B1 and FANS 1/A(+) ground stations when:
• Aircraft equipped with ATN B1 and FANS 1/A(+) data link system also incorporates interoperability requirement IR-207, IR-209, IR-210, IR-211, IR-212, IR-214, and IR-215 of DO-305A/ED-154A.
• ATN B1 ground station incorporates interoperability requirement IRec-1 and IR-213 of DO-305A/ED-154A.
• FANS 1/A(+) ground station incorporates interoperability requirement IR-208 of DO-305A/ED-154A.
Otherwise, the pilot will lose their data link service requiring the pilot to manually perform a logon/notification to reestablish ATSU data link service.
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Interoperability Designator Description Note 3: Seamless transition of ATSU data link service occurs between B2 and FANS 1/A(+) ground stations when:
• Aircraft equipped with B2 and FANS 1/A(+) data link system also incorporates interoperability requirement NIR-153, NIR-155, NIR-156, NIR-157, NIR-158, NIR-160, and NIR-161 of DO-352A/ED-229A.
• B2 ground station incorporates interoperability requirement NIRec-3 and NIR-159 of DO-352A/ED-230A.
• FANS 1/A(+) ground station incorporates interoperability requirement NIR-154 of DO-352A/ED-229A.
Otherwise, the pilot will lose their data link service requiring the pilot to manually perform a logon/notification to reestablish ATSU data link service.
Note 4: To allow a FANS 1/A(+) data communication system on an aircraft to communicate with an ATN B1 data communication system at an ATSU, the ATSU ground system needs to accommodate the FANS 1/A(+) aircraft by incorporating the interoperability requirements of DO-305A/ED-154A.
Note 5: To allow a FANS 1/A(+) data communication system on an aircraft to communicate with a B2 data communication system at an ATSU, the ATSU ground system needs to accommodate the FANS 1/A(+) aircraft by incorporating the interoperability requirements of DO-352A/ED-230A.
ATN B1 ATS applications CM and CPDLC supported by ATN B1:
a) CM is a data link application providing DLIC.
b) CPDLC (Version 1) for ACM, ACL, and AMC.
Note 1: Interoperability for DCL, downstream clearance (DSC), D-ATIS, and flight plan consistency data link services, which are defined in DO-280B/ED-110B are not supported.
Note 2: Seamless transition of ATS data link service between ATN B1 and FANS 1/A+ ground stations when:
• Aircraft equipped with ATN B1 and FANS 1/A+ data link system also incorporates interoperability requirement IR-207, IR-209, IR-210, IR-211, IR-212, IR-214, and IR-215 of DO-305A/ED-154A.
• ATN B1 ground station incorporates interoperability requirement IRec-1 and IR-213 of DO-305A/ED-154A.
• FANS 1/A+ ground station incorporates interoperability requirement IR-208 of DO-305A/ED-154A.
Otherwise, the pilot will lose their service requiring the pilot to manually perform a logon/notification to reestablish ATS data link service.
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Interoperability Designator Description Note 3: To allow a FANS 1/A+ data communication system on an aircraft to communicate with an ATN B1 data communication system at an ATSU, the ATSU ground system needs to accommodate the FANS 1/A+ aircraft by incorporating the interoperability requirements of DO-305A/ED-154A.
Note 4: To allow an ATN B1 data communication system on an aircraft to communicate with a B2 data communication system at an ATSU, the ATSU ground system needs to accommodate the ATN B1 aircraft by incorporating the interoperability requirements of DO-353A/ED-231A.
Note 5: To allow a B2 data communication system on an aircraft to communicate with an ATN B1 data communication system at an ATSU, the B2 data communication system on the aircraft needs to accommodate the ATN B1 ground system by incorporating the interoperability requirements of DO-353A/ED-231A.
B2 Version of the Baseline 2 Data Communication system described in this section. The United States plans to use B2, as defined in AC 20-140C, as part of FAA’s NextGen initiative. An aircraft equipped with B2 is fully interoperable with any B2 ground station.
Aircraft equipped with a version of B2 other than that defined by AC 20-140C are not eligible for the B2 interop designator. B2 is comprised of the following data link applications and data link services.
a) CM is a data link application supporting the following data link service: DLIC.
b) CPDLC (Version 3) is a data link application supporting the following data link services: ACM, Clearance Request and Delivery (CRD), AMC, DCL, Data Link Taxi (D-TAXI), Oceanic Clearance Delivery (OCD), 4DTRAD, IER, In-Trail Procedures (ITP), IM, and DRNP.
c) ADS-C (Version 2) is a data link application supporting the following data link services: 4DTRAD, IER, Position Reporting (PR), IM, and DRNP.
Note 1: To allow a FANS 1/A+ data communication system on an aircraft to communicate with a B2 data communication system at an ATSU, the ATSU ground system needs to accommodate the FANS 1/A+ aircraft by incorporating the interoperability requirements of DO-352A/ED-230A.
Note 2: To allow an ATN B1 data communication system on an aircraft to communicate with a B2 data communication system at an ATSU, the ATSU ground system needs to accommodate the ATN B1 aircraft by incorporating the interoperability requirements of DO-353A/ED-231A.
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Interoperability Designator Description Note 3: To allow a B2 data communication system on an aircraft to communicate with an ATN B1 data communication system at an ATSU, the B2 data communication system on the aircraft needs to accommodate the ATN B1 ground system by incorporating the interoperability requirements of DO-353A/ED-231A.
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Table 2-3. Types of Data Link Systems and Operations Aircraft Equipment and Capability
ACARS ATS (ATSU Ground Data Link System) CADS or AOC (ATSU Ground Data Link System) FANS 1/A (ATSU Ground Data Link System) ATN B1 (ATSU Ground Data Link System) FANS 1/A– ATN B1 (ATSU Ground Data Link System)
ACARS ATS ATC communication
• DCL or PDC
• OCL Flight information
• D-ATIS
N/A N/A N/A N/A FANS 1/A ADS-C N/A Surveillance
• ADS-C (CADS) Surveillance
• ADS-C
N/A N/A FANS 1/A N/A Surveillance
• ADS-C (CADS) ATC communication
• CPDLC Surveillance
• ADS-C
N/A ATC communication
• CPDLC for
ACM, ACL, and AMC data link services FANS 1/A+ N/A Surveillance
• ADS-C (CADS) ATC communication
• CPDLC Surveillance
• ADS-C
N/A ATC communication
• CPDLC for
ACM, ACL, and AMC data link services ATN B1 N/A N/A N/A ATC communication
• CPDLC for
ACM, ACL, and AMC data link services ATC communication
• CPDLC for
ACM, ACL, and AMC data link services FANS 1/A– ATN B1 N/A Surveillance
• ADS-C (CADS) ATC communication
• CPDLC Surveillance
• ADS-C ATC communication
• CPDLC for
ACM, ACL, and AMC data link services ATC communication
• CPDLC for
ACM, ACL, and AMC data link services Note: B2 will be included at a later date.
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