Flight Data Readouts: What are Data Link Communications and Recordings?

An Introduction to Data Link Recording and Communications

In An Introduction to Flight Data Readouts, we introduced data link recording (DLR) as recordings that capture communications between aircraft and ground-based systems. These recordings of the data link system aboard the aircraft track anything from messages, flight plans, weather updates, surveillance data, and operational notifications. This is referred to as data link recording (DLR), and, in most cases, data link recording is done via the Cockpit Voice Recorder (CVR).

What are Data Link Communications?

Simply put, data link communications are characterized by any information relayed from the aircraft to the ground or from aircraft to aircraft. Specifically, these data link systems include information shared over networks like the Aircraft Communication Addressing and Reporting System (ACARS) and the Aeronautical Telecommunications Network (ATN). Both networks utilize high-frequency (HF) or very high-frequency (VHF) data link and satellite communications to send messages.

In most cases, pilot to Air Traffic Control (ATC) communications are made via the ACARS data link system due to this system being available over transoceanic flights. Due to this, most Future Air Navigation System (FANS) avionics are ACARS-based.

The Purpose of Data Link Communications

Data link communications have a variety of purposes, from providing constant positioning and communication during transoceanic flights to enabling aircraft to receive various clearances. In most cases, aircraft utilize the Future Air Navigation (FANS) 1/A (+) designed avionics for their data link communications. This provides them access to the Controller Pilot Data Link Communication (CPDLC) application for contact with ATC and enables Automatic Dependence Surveillance-Contract (ADS-C) positioning systems and flight reporting, which sends information to the Air Traffic Service Unit (ATSU).

Enabled by ACARS, these communications systems can track the following:

Out of the gate, off the ground, on the ground, and into the gate (OOOI) events. The data link system can determine the flight phase, the time it occurred, and other information related to the flight, such as the fuel status and the flight’s origin.

Flight Management Systems (FMS). This is the communication system for flight plans and weather information to be sent from the ground to the aircraft – enabling the flight crew to evaluate changes to weather conditions and access alternative flight paths.

Equipment Health and Maintenance Information. The health of the aircraft can be monitored via these data link systems and sent to the ground in real time. This data provides detailed messages to the ground stations, which can be used for monitoring aircraft and onboard avionics health.

Ping Messages. These automated messages provide information regarding the aircraft’s connection to ensure the ATC can continue to reach the aircraft successfully.

Any Manually Sent Message. Since ACARS interfaces with the interactive display units in the cockpit, it can track when flight crews send and receive technical messages and reports to or from the ground. This allows it to track any messages between aircraft and the ground.

What is Included in a Data Link Recording Readout?

When a CVR records data link messages, they record the data link messaging for the same duration they record cockpit voice data. Therefore, most data link communications are recorded for at least 2 or 25 hours, depending on the aircraft’s route, weight, and the regulatory body they operate under. In a data link readout, the airline would receive a report detailing what was communicated via the data link system (ACARS) and critical onboard maintenance systems (OMS) information recorded in flight.

This report involves a data link message observation check to ensure that message content was accurate, proper procedures were followed, communication was not delayed, and the communications were comprehensible. It will also involve an OMS message observation check to determine whether the equipment health and maintenance data messages monitored during the flight were sent using the correct procedures, accurate to the needed maintenance, and were not delayed during transmission. A comprehensive readout service will provide all this information in its data link messaging readout.

Information provided in a data link readout service benefits those not only trying to meet regulatory requirements but also those looking to understand flight crew to ATC communications and gain a better understanding of aircraft health and maintenance. These DLR readouts complement the information gained from the CVR and FDR readouts to give a broader picture of how aircraft and flight crew operate. These various readout services provide essential information to benefit aircraft operations and satisfy aircraft safety requirements.

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