Data Communications Between The Air and The Ground

To ensure safe and efficient air traffic management, aeronautical communications, navigation, and surveillance systems are essential. The safety of the air depends on the accuracy and timeliness of radio communications, both voice and data links. All types of communication tools are used by iJET in ground handling before and during flight to ensure the safety of the flight.

As a means of communication between the air to the ground communication, radar continues to be a valuable tool. Transponders act as identification tools for aircraft, allowing ATC towers to identify them immediately. In order to work, they recognize radar frequencies as they interact with the plane. By responding with a signal of its own, the transponder alerted by the radar identifies the aircraft in the Tower. By using transponders, other aircraft and the ground can be avoided from colliding.

Voice-Over-Air Communications

Radio telephony has traditionally been used to communicate voice and audio between aircraft and the ground, broadcasting and receiving on:

• UHF
• VHF
• HF

As an alternative, SATCOM and VOIP through the Internet can be used to conduct voice communications.

Ultra High Frequency (UHF)

The Air Traffic Control System uses Ultra High Frequency (UHF) radio stations to communicate air-ground voice with military aircraft in operational air traffic (OAT) as well as to handle non-8.33 kHz State aircraft operating in 8.33 kHz airspace under General Air Traffic/Instrument Flight Rules (GAT/IFR).

Very High Frequency (VHF)

VHF, or very high frequency, is a conventionally defined portion of the electromagnetic spectrum with wavelengths of 1 to 10 metres and frequencies between 300 and 30 megahertz. VHF Omnidirectional Radio Ranges (VORs) operate in the VHF band and provide aircraft navigation information. The VOR broadcasts a VHF radio composite signal, which includes the station’s Morse Code identifier (and sometimes a voice identifier) as well as information to calculate the magnetic bearing from the station to the aircraft.

High Frequency (HF)

A high frequency band (HF) is a range of radiofrequency electromagnetic waves (radio waves) between 3 megahertz (MHz) and 30 megahertz (MHz) designated by the International Telecommunications Union (ITU). Shortwave radio stations (3.95–25.82 MHz) use the band for aviation communications, meteorological stations, amateur radio, and citizen band services.

System for Airborne Communications, Addressing, and Reporting

A digital data link system, ACARS, has been in use since 1978 to transmit messages between aircraft and ground stations. The system initially relied solely on VHF channels, but in recent years, alternative means of data transmission have greatly enhanced its geographical coverage. A rapid trend has also emerged towards integrating aircraft systems with ACARS. Both factors have led to a rapid increase in its use as an operational communication with aircraft tool.

Information Contained In the Message

Depending on their content, ACARS messages may fall into three categories:

• Air Traffic Control (ATC)
• Aeronautical Operational Control (AOC)
• Airline Administrative Control (AAC)

Air Traffic Control (ATC)

Clearance requests and instructions to aircraft are included in ATC messages. Pre-Departure, Datalink ATIS, and Oceanic Clearances are often delivered through them. Even though ACARS is used as a ‘niche’ system in ATC communications, it is not considered suitable for use in the broader use of datalinks for ATC communications, such as Controller Pilot Data Link Communications (CPDLC).

Aeronautical Operational (AOC) and Airline Administrative Control (AAC)

The AOC and AAC messages are used to communicate between an aircraft and its base. ARINC Standard 618 requires that all messages meet at least the requirements of ARINC Standard 618, regardless of whether they are in standard form or defined by users. The content of the message can be anything, including the following examples:

• Final load and trim sheets are uploaded to the aircraft
• Information about weather or NOTAMs
• Obtain status, position, time, and any diversions from the aircraft
• Data downloads including automatic triggers that inform about aircraft system failures and exceedances
• This includes information regarding catering uplift, special advice for passengers, and ETAs.

The Aircraft Equipment

Management Units (MUs) and Communications Management Units (CMUs) are two ACARS equipment components found on board aircraft. Data is transmitted or received by this device externally, as well as internally in more advanced systems.

If there are several air-ground transmission methods available, the ACARS MU/CMU may select the most efficient one automatically. The flight deck will be equipped with a printer and the cabin crew may also have access to a terminal. It is usually through a CDU that a member of the flight crew can access the ACARS system, in addition to the MU/CMU, which is accessed by a CDU in more advanced systems.

Equipment on the aircraft

Aircraft ACARS equipment consists of MUs and CMUs. MUs are the Management Units and CMUs are the Communication Management Units. An external router or, in more advanced systems, an internal router is used to transmit and receive data.

In the event that a choice is available for ACARS MU/CMU, it may be automatically selected as the most efficient method for air-ground transmission. It is possible to have a cabin crew terminal and a printer on the flight deck. In advanced ACARS systems, flight crews can access up to seven different systems, including the FMS, in addition to the MU/CMU, via the CDU. The CDU generates different display pages for each system connected and accepts keyboard input when selected. CDU access may be substituted with some EFBs. CDU access may be substituted with some EFBs.

Providers

By using a radio link, a Datalink Service Provider (DSP) conveys messages between its own ground routing system and a radio link to/from its own ground network. Three data link methods are available for transmitting ACARS messages:

• Line-of-sight is the limitation with VHF or VDL (VHF Data Link)
• SATCOM which is not available in polar regions
• The HF or HFDL (HF Data Link) has been added especially for communications in polar regions

It is ARINC and SITA that are the primary DSPs. It used to be that each region of the world had only one DSP, but now there are more and more competitive offerings.

Ground Processing Systems

A participating ANSP (Air Navigation Service Provider) or an aircraft operator is responsible for providing the ground system. DSPs or separate service providers often handle this function on behalf of aircraft operators. Especially automatically generated messages can be configured to be delivered to the appropriate recipient according to the message type, just as ground-originated messages can be configured to reach the appropriate aircraft.

To ensure secure ground operations, the iJET ground communication team performs full-time checks of Air Navigation Service Providers (ANSPs) and Data Link Service Providers (DSPs).