and responding to the clearances. Additionally, this guide provides general information on the use of data link communications during en route operations.
8. Data Link Communication Compliance Guide. This guide expedites the compliance process as it condenses into one location the information required for data link operations.
1.10 Airworthiness. For airworthiness guidance for new aircraft and systems, refer to AC 20-140( ).
1.11 Regulatory Basis for Data Link Communication. CPDLC is an acceptable method of delivering and accepting an ATC clearance in accordance with part 91, § 91.123.
With data link communication technology, both digital and voice communication are available to ATC and the pilot. Depending on the operation, data link communication may be the most suitable method of communication as deemed necessary for ATC and pilot purposes.
1.11.1 CPDLC Compliance and Voice Communication. CPDLC is not sufficient as a means of compliance to the voice communication equipment requirements as per §§ 91.129,
91.130, 91.131, 91.135, 91.205, and 91.511; part 121, §§ 121.99 and 121.122; and part 135, § 135.165, and is not required by these rules. For data link communications, two-way radio voice communication or other means of communication approved by the FAA must also be available.
1.11.2 Flight Plan Filing and Data Link Communication Capability. Pilots and operators must file an accurate flight plan in accordance with §§ 91.169 and 91.153(a)(9). The Air Traffic Service Unit (ATSU) evaluates flight plan designator(s) to provide filed services.
Pilots and operators should use the guidance in this AC and other appropriate documents to determine the data link communication designator(s) for their route (see Appendix D).
1.11.3 Cockpit Voice Recorder (CVR) and Flight Data Recorder (FDR). Operators must comply with the CVR and FDR requirements of §§ 91.609(j), 121.359(k), and 135.151(h), and part 125, § 125.227(i). FAA Information for Operators (InFO) 16004 provides additional guidance concerning the applicability of these regulations.
1.12 AC Feedback Form. For your convenience, the AC Feedback Form is the last page of this AC. Note any deficiencies found, clarifications needed, or suggested improvements regarding the contents of this AC on the Feedback Form.
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CHAPTER 2. DATA LINK COMMUNICATION OVERVIEW
2.1 Introduction. This chapter is intended to be informative for those not familiar with data link communication. For those already knowledgeable, Chapters 3 through 8 of this AC are devoted to data link eligibility and use.
2.2 What Are Data Link Communications? “Data link” is a generic term encompassing different types of data link systems and subnetworks. Figure 2-1, Overview Data Link System, provides an overview of a data link system, including subnetworks. While many data link capable aircraft have access to very high frequency (VHF) data link (VDL), not all aircraft have access to additional satellite and/or high frequency (HF) data link capability. Similarly, not all communication service providers (CSP) have HF data link capability.
Figure 2-1. Overview Data Link System
2.2.1 Aircraft Communication Addressing and Reporting System (ACARS) and Aeronautical Telecommunications Network (ATN). There are ACARS-based applications and ATN-based applications. The VDL Digital Link Mode 2 subnetwork supports both ACARS-based and ATN-based applications. The other subnetworks listed in this section support ACARS-based applications only. Controller Pilot Data Link Communication (CPDLC) and Automatic Dependence Surveillance-Contract (ADS-C) can be Future Air Navigation System (FANS) 1/A(+) or ATN-based. The FANS 1/A-based services are used over the ACARS networks and the ATN-based services are used over the 2-1
ATN networks. The ACARS and ATN networks are not compatible. This AC concentrates on CPDLC and ADS-C using FANS 1/A(+) unless specifically denoted as ATN.
2.2.2 Data Link Subnetwork. Data link systems send messages over several communication subnetworks:
• VDL Mode 0/A (i.e., ACARS),
• VDL Mode 2,
• Satellites, and/or
• High Frequency Data Link (HFDL).
2.2.3 Data Link Systems. Data link communications is a means of transmitting and receiving digital information. ATS data link systems include the following:
• FANS 1/A(+),
• ATN Baseline 1 (B1),
• Baseline 2 (B2), and
• ACARS Air Traffic Service (ATS).
2.3 FANS. FANS 1/A is ACARS-based and provides direct data link communication between the pilot and the air traffic controller via FANS 1/A avionics and FANS 1/A ground end systems. In the early 1980s, International Civil Aviation Organization (ICAO) began an effort to establish data link architecture under its FANS structure.
Boeing developed FANS 1 to DO-219 and ARINC 745 using ARINC 622 binary character data format followed by Airbus with its FANS A. These two systems are referred to as FANS 1/A. The “+” at the end of FANS 1/A indicates an updated system version that includes a message latency monitor to detect old messages that may no longer apply. FANS messages can be sent over a variety of subnetworks depending on:
• Aircraft equipment,
• Configuration/media management, and
• Subnetwork availability.
2.4 CPDLC and ADS-C.
2.4.1 CPDLC. CPDLC is a means of communication between controller and pilot, using data link for air traffic control (ATC) communications. Messages from an aircraft to the Air Traffic Service Unit (ATSU) may follow a standard format or may be free text.
Messages from a controller normally follow a standard format and usually require a response from the pilot (see Appendix F, Controller Pilot Data Link Communication 2-2
(CPDLC) Uplink and Downlink Tables, for uplink message (UM) and downlink message (DM) sets).
2.4.2 ADS-C. ADS-C is an automated surveillance information system that sends position and other flight reports to the ATSU. After initial logon/notification, a link is established between the ground system and the aircraft. Without pilot input, the oceanic ATSU/Aeronautical Operational Control (AOC) can establish a “contract” with the aircraft to receive reports of aircraft identification, aircraft position, altitude, Mach number, vertical rate, true track, magnetic heading, ground speed, navigation waypoints, and meteorological data.
2.4.2.1 ADS-C Contract Types. Depending on the aircraft type, there can be up to five separate connections to different ground facilities (i.e., ATSU/AOC) at any one time. Each connection can have one Periodic contract, one Event contract, and one Demand contract.
1. Periodic. The ATSU can set or alter the update rate or time interval as needed (a higher update rate is usually required in high traffic areas or associated with reduced separation).
2. Event. The aircraft system will communicate an event as established by the ATSU if there is a change in waypoint, vertical rate, lateral deviation or altitude. An event contract remains in effect until the ATSU cancels it or until the event(s) used to trigger the report occurs. The waypoint change event contract will trigger a report for all waypoint changes. All other event contracts will trigger a report on the first occurrence and then, if necessary, the ATSU will need to request a new event contract indicating all desired event types. (See Figure 2-2, ADS-C Event Sequence.)
3. Demand. The ATSU can request a single update as needed. This does not affect an existing contract preset rate.
Figure 2-2. ADS-C Event Sequence
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2.4.2.2 ADS-C Emergency. An ADS-C emergency can be triggered by the pilot by the following means:
1. Manually, by selecting the ADS-C emergency function;
2. Indirectly, by triggering another type of emergency alerting system
(e.g., transmission of a CPDLC emergency message or selection of a Secondary Surveillance Radar (SSR) emergency code); and
3. Covertly (The availability of that functionality may vary between aircraft types).
Note: Once an ADS-C emergency has been triggered, under normal circumstances, the avionics will continue to transmit ADS-C emergency periodic reports until the pilot de-selects the ADS-C emergency function.
2.5 ATN. ATN is an inter-network architecture permitting ground, air-ground, and avionics data subnetworks to exchange digital data for the safety of air navigation and for the regular, efficient, and economic operation of ATS. ATN is in limited use in Europe, but not available in U.S. domestic airspace. The system is terrestrial based and not available over oceanic and remote continental areas.
2.5.1 ATN B1. ATN B1 consists of the following:
• Context management (CM) application for Data Link Initiation Capability (DLIC) service; and
• CPDLC application for ATC Communication Management (ACM), ATC Clearance (ACL), and ATC Microphone Check (AMC) services.
2.6 B2. B2 is ATN-based and will enable extended capabilities not possible with ATN B1 or FANS 1/A(+) as shown in Table 2-2, Interoperability Designators and Descriptions.
The FAA plans to implement the B2 CM, CPDLC, and ADS-C ATN-based applications over the Internet Protocol Suite. B2 will provide additional services such as:
1. CPDLC:
• Initial Four-Dimensional (4-D) Trajectory Data Link (4DTRAD),
• Dynamic Required Navigation Performance (DRNP), and
• Advanced flight Interval Management (IM).
2. ADS-C:
• Extended Projected Profile (EPP) information provided in ADS-C reports supporting Information Exchange and Reporting (IER), 4DTRAD, and DRNP services.
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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