​Controller Pilot Data Link Communications - Contract (CPDLC)

​ADS, CPDLC, ATC COM, ACARS, AOC, Whaaah? Here's how we keep this straight:

• ADS-B Out — You can think of Automatic Dependent Surveillance - Broadcast Out (ADS-B Out) as a higher tech replacement for your transponder. ADS-B OUT sends your GPS position to air traffic control and other aircraft equipped with ADS-B In. It is much more accurate than a radar blip. 


• ADS-B In — You can think of Automatic Dependent Surveillance - Broadcast In (ADS-B In) as a more accurate version of your TCAS. While TCAS aircraft positions shown in your cockpit are approximate, ADS-B In positions are exact.


• ADS-C — You can think of Automatic Dependent Surveillance - Contract (ADS-C) as a replacement for Air Traffic Control radar contact. When you have logged on to an Air Traffic Service Unit with ADS-C, you have agreed to contracts which send information to the ATSU, such as your position, on a regular basis. 


• CPDLC — You can think of Controller Pilot Data Link Communications as a replacement for your HF when oceanic and VHF over some domestic areas. It is far superior to your HF and has distinct advantages over VHF.


• ATC COM, ACARS, AOC — Air Traffic Control Communications (ATC COM) is Honeywell-speak for CPDLC. Aircraft Communication Addressing and Reporting System (ACARS) used to be Airline Communication Addressing and Reporting System and is simply communications through a data service provider and includes your PDC, digital ATIS, and most of your oceanic clearances. Aeronautical Operational Control (AOC) is Gulfstream-speak for ACARS.

Purpose

The role CPDLC plays in the Future Air Navigation System is to reduce the time it takes for air traffic control to issue instructions to a pilot and the pilot to acknowledge. In a domestic environment this is rarely a problem. When oceanic, however, it can be a factor. Reducing that time, known as Required Communications Performance (RCP), allows ATC to reduce aircraft spacing.
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The concept of RCP relates to the communications component of the communication, navigation, and surveillance/air traffic management (CNS/ATM) framework and complements Required Navigation Performance (RNP) and Required Surveillance Performance (RSP). In general, the requirements for operation in a defined airspace or performance of a defined procedure include elements of CNS functionality and performance, as well as ATM functionality and performance. The guidance provided in this AC regarding RCP is consistent with ICAO Doc 9869, Manual on RCP. RCP is a statement of the performance requirements for operational communication in support of specific ATM functions. The RCP is determined by cognizant authorities in consideration of air traffic operations, target levels of safety, separation assurance, Flight Standards Service (AFS), and functional hazard analysis associated with the airspace, operation, or procedure. Thus, RCP is operationally derived and not based on any specific technology, or combination of technologies, that may be utilized for communications. The performance of a communications is generally accepted as comprising communication transaction time, integrity, continuity, and availability.

​            RCP Type    - Satisfies requirements as

• RCP 240    - Normal means of communication for application of 30 NM lateral separation and reduced longitudinal separation minima
• RCP 400    - Alternative means of communication for application of 30 NM lateral separation and reduced longitudinal separation minima
• RCP 400    - Normal means of communication for application of lateral separation greater than or equal to 50 NM and time-based longitudinal separation

​The bottom line on CPDLC, then, if you can reduced the round trip time between the issuing of the message from ATC and the reception of the pilot's reply to 240 seconds or less, you can reduce the lateral and longitudinal spacing.

Domestic CPDLC — A Caveat
What about domestic CPDLC? How is it different than oceanic CPDLC? You obviously have a perfectly good VHF over most domestic regions but there is more to it than that. You have more airplanes and you need to communicate more quickly. The RCP type is understandably much quicker:

ICAO GOLD

• RCP Specification: RCP 150
• Interoperability: ATN B1, ATN B1-FANS 1/A

If we could add on to the previous table it would look like this:

            RCP Type    - Satisfies requirements as

• RCP 150    - Normal means of communication for domestic airspace

The CPDLC you use while oceanic might not be good enough for domestic operations.

Oceanic CPDLC versus Voice

• When operating within airspace where CPDLC is available and local ATC procedures do not state otherwise, CPDLC should be the primary means of communication. Voice should be used as the backup communication medium (e.g. direct VHF, direct HF, third party HF, Satellite voice).


• While the CPDLC message set defined in Appendix A provides for ATC communications, voice may be a more appropriate means depending on the circumstances, e.g. some types of non-routine communications. Refer to paragraph 5.8 for guidelines on use of voice and data communications in emergency and non-routine situations.


• During an emergency, the flight crew would normally revert to voice communications. However, the flight crew may use CPDLC for emergency communications if it is either more expedient or if they are unable to establish voice contact.


• The response to a CPDLC message should be via CPDLC, and the response to a voice message should be via voice.


• If a conflicting CPDLC and voice clearance/instructions is received, the flight crew should obtain clarification using voice.


• If the intent of an uplinked message is uncertain, the flight crew should reject (UNABLE) the message. The flight crew may use either CPDLC or voice to confirm the intent of the message.


• Regardless of whether CPDLC is being used as the primary means for communication, the flight crew should continuously monitor VHF/HF/UHF guard frequency. In addition, the flight crew should continuously maintain a listening or SELCAL watch on the specified backup or secondary frequency (frequencies). On aircraft capable of two SATCOM channels, one channel may be selected to the phone number for the radio facility assigned to the current flight information region (FIR) to enable timely voice communications with ATS. The second channel may be selected to the company phone number to enable timely voice communications with company dispatch.

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If you have CPDLC and you are in airspace where CPDLC is being used, you should use CPDLC as primary, voice communications as secondary. The general rule of thumb is: if contacted by CPDLC, respond with CPDLC; if contacted by voice, response with voice. When oceanic you still need to check in with HF, get a good SELCAL check, and maintain a listening watch if SELCAL fails.

Domestic CPDLC versus Voice

Implementation of CPDLC into continental airspace is intended as a supplement to the use of VHF voice and the intent is to build a single communications environment where both voice and CPDLC are considered as being normal Air Traffic Management (ATM) tools.
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FANS-1/A Operations Manual

• The following procedures only apply to normal (non-emergency) operations. While the intent of these procedures is to develop a standardised and predictable environment using a combination of voice and CPDLC, the decision on whether voice or CPDLC is the more appropriate medium for use in a given operational situation will be made by the pilots and controllers involved.


• As a supplement to VHF voice, CPDLC is intended to be restricted to the passing of strategic information. Strategic information involves routine, non-time-critical communications, and includes examples such as the passing of amended flight levels, amended routes, speed control messages, frequency changes, and SSR codes, when the speed of delivery is not critical to safety.


• Voice instructions and acknowledgments shall have precedence over CPDLC messages at all times. In the event that any ambiguity exists in a message or message exchange, then the controller/pilot shall revert to voice communications for clarification.


• Flight crew shall either comply with uplink CPDLC instructions or respond with UNABLE, and shall respond to uplink messages using CPDLC whenever possible.

​You might not be able log in to CPDLC domestically over Europe, depending on your CPDLC. 

Actual practice over domestic Europe:

• Log on to CPDLC where you can.
• Use CPDLC for all routine issues.
• Confirm via voice any CPDLC instruction that changes the aircraft altitude, heading, or airspeed, adding the term "datalink" to let the controller know where the instruction came from. Example:
  • (Via CPDLC) CLIMB TO FL 290
  • (Via VHF) "London Control, November seven seven zero zero, data link climb flight level two niner zero."
• Do not use ADS-C domestically.

Oceanic CPDLC versus Domestic CPDLC (That Whole "Protected Mode" Debate)

Nomenclature

• ACARS ATS — ATS applications, departure clearance (DCL), oceanic clearance (OCL) and data link – automatic terminal information service (D-ATIS), supported by aircraft communications addressing and reporting system (ACARS).


• FMC WPR — Flight management computer waypoint position reporting (FMC WPR)


• FANS 1/A — Initial future air navigation system (FANS 1/A) ATS applications, CPDLC and ADS-C, supported by FANS 1/A over ACARS.


• ATN B1 — ATS applications, CM and CPDLC, supported by aeronautical telecommunication network – baseline 1 (ATN B1):


• VDL M2 — Very high frequency data link – mode 2

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• The ATN B1 data link system relies on the aeronautical telecommunication network (ATN), which is provided and maintained by various communication service providers (CSPs) and/or ANSPs.


• The ATN relies only on VHF (VDL M2) to meet the performance required for the intended operations.

So, how about all this in English?

1. Most aircraft certified, equipped, maintain, and operated in the United States will have installed an older version of CPDLC called Future Air Navigation System (FANS 1/A) with Air Traffic Services (ATS) applications, ATC Facilities Notification (AFN), CPDLC and ADS-C.


2. Many aircraft certified, equipped, maintained, and operated outside the United States recently, as well as many recently certified in the United States, will have installed a newer version of CPDLC that adheres to a newer standard called Aeronautical Telecommunications Network Baseline 1 (ATN B1).


3. A part of the newer standard that is probably not installed on FANS 1/A aircraft is Very High Frequency Data Link Mode 2 (VDL M2), sometimes called "protected mode VHF Data Link" (PM CPDLC).


4. You can operate in most (if not all) oceanic and remote airspace with a FANS 1/A aircraft, even if you do not have VDL M2. This capability carries into at least the first domestic ATSU, since they are responsible for the transition to and from oceanic.


5. You may find yourself without CPDLC coverage domestically if you do not have ATN B1 and VDL M2. Most European countries specifically say "log-on from FANS 1/A or non-PM CPDLC capable aircraft will not be accepted.


6. You can find rules and regulations that say PM CPDLC is, or will become, mandatory. Some manufacturers, such as Gulfstream, managed to secure exemptions for their entire fleet of aircraft.

Why Europe is Different

• As a key component of the Single European Sky, the European Community has mandated operational use of air-ground data link, in the form of “Protected Mode” Controller Pilot Data Link Communications (PM-CPDLC), for aircraft flying above 28,500 feet (FL285).


• Although complex in name, PM-CPDLC is straightforward in practice. The system is similar to text messaging on cell phones, allowing pilots and Air Traffic Control (ATC) to send pre-set or “canned” data messages between the ground and the aircraft. CPDLC messages enable automation of routine tasks that can take up to 50 percent of a controller’s time. Using data link systems can also mitigate common communication problems such as unclear radio communication or misinterpretation due to language differences or poor clarity.


• Indeed, studies within the European Community have confirmed the capability of datalink services to provide additional air traffic control capacity. Datalink solutions provide airline and business aircraft operators with significant benefits at reduced cost, including enhanced flight operations efficiency and lower airline maintenance, administration and air traffic control costs.


• Once all the modernization initiatives are complete, this should lead to a threefold increase in airspace capacity and a 50 percent reduction in air navigation costs.

Exemptions
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• Feb. 5, 2015 — By this date, all aircraft operating within European airspace above FL 285 must be equipped with a compliant PM-CPDLC datalink system (aircraft built before 1997 and which will be removed from service by December 31, 2017 are exempt from this requirement). Some business aircraft which will remain in service after this date are also permanently exempted.

Protected Mode CPDLC over VHF Data Link (VDL Mode 2) was initially packaged with a program known as Link 2000+. Though the implementation dates tend to slip, if you want to fly about 28,500' in Europe you either need it installed or you need an exemption. You need to contact your aircraft manufacturer to find out where you stand.
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The Gulfstream world used to be pretty cut and dried. The GIV and GV do indeed have lifetime exemptions. The G450 and G550 were said to have also been given lifetime exemptions based on installation of equipment needed to be FANS 1/A qualified. That might have changed depending on how you read Gulfstream literature. The latest "Avionics Update," available at http://www.mygulfstream.com/, says the G450 is qualified "holding release ASC 092" and the G550 "holding release ASC 115." These are both described as "Protected Mode CPDLC Installation." As of October 2016, neither ASC is available and Gulfstream has both on hold. (They were announced in 2014.) Reading between the lines I would say we are exempt until those ASC's are released, and then we have to install them.

PM CPDLC/Link 2000+ Implementation Schedule

Flight Crew Response Times

• System performance requirements have been established to support reduced separation standards. Specific latency times have been allocated to the technical performance, based on flight crew and controller response times. Regional/State monitoring agencies monitor performance to ensure the technical and operational components of the system meet required standards. To support RCP 240 operations (e.g. 30 nautical mile longitudinal separation) the flight crew should respond to an uplink message within one minute.


• Flight crew procedures should be developed to respond to uplinks as soon as practical after they are received. For most uplinks, the flight crew will have adequate time to read and respond within one minute. However, the flight crew should not be pressured to respond without taking adequate time to fully understand the uplinked message and to satisfy other higher priority operational demands.


• If the flight crew determines they will need a significant amount of time to respond to a message, they should send a STANDBY response.

It is said that if they don't hear back from you in sixty seconds, they will consider the communications lost and if a clearance was involved, that clearance is cancelled. I've not seen that in writing but the threat is clear: respond within a minute, use "STANDBY" if you must. When dealing with clearances, I usually hit the print button, send the acknowledge, and then read the contents. I figure I can always respond a second time if I have to.
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Multiple CPDLC Contacts

​An aircraft can have a maximum of two CPDLC connections established concurrently, each with a different ATSU. Only one CPDLC connection can be active at any given time; any second connection is inactive.

An ATSU system may request multiple simultaneous ADS contracts to a single aircraft, including one periodic and one event contract, which may be supplemented by any number of demand contracts. Up to five separate ground systems may request ADS contracts with a single aircraft.
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You can only have one active CPDLC connection, think of it as your actual air traffic control contact. But you can have two connections, usually the active connection and the "next."

CPDLC CQZX Active, EGGX Next

Position Reports at FIR Boundaries

When notified that a new active CPDLC connection has been established, and if entering an FIR that requires the crew to send a CPDLC position report to confirm current data authority status (refer Appendix E, paragraph E.2.2), the flight crew should send a CPDLC position report without delay unless advised through a CONTACT or MONITOR instruction of a specific transfer point.
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This is often taught this way: "Send a position report whenever entering oceanic airspace, except in the North Atlantic," meaning the North Atlantic is the only exception. In fact, the rule seems to be: "Send a position report crossing an FIR boundary if Appendix E tells you to."