ACARS stand for Aircraft Communication Addressing and Reporting System. This system allows aircrafts to communicate and report to the ground and vice-versa. It does so by transmitting data on VHF frequencies that can be received and decoded. It is a digital datasystem in VHF (Aviation). It makes it possible for aviation companies to "communicate" and track the planes of their fleet. This system is being used by a lot of large aviation corporations and can be said to be the 'E-mail' for the planes. The plane's call sign is used as the address for the destination of the message. Before ACAR was developed, all the flight messages were voiced and that made things slow and painful. The development of ACAR by Aeronautical Radio Inc. made possible the routine-messages, about departure, arrival, cargo, fuel etc. To only take a short time to transmit.

The Aeronautical Radio, Inc. (ARINC) maintains a huge worldwide VHF and HF voice network to provide operational radio communications for the aircraft industry. ACAR was designed and developed in the early eighties. It was produced to reduce the flight crew's workload by using modern computer technology to exchange many routine reports and messages. ACARS uses the AM mode because the same airborne VHF radio is often also used for voice communications. Burst transmissions are used with a limit of 220 characters per message. Transmissions often last less than one second. (Website)

An ACARS is a lot like amateur radio packet. It's a digital data link system transmitted via VHF and HF radio that allows airline flight operations departments to communicate with the various aircraft in their fleet. This VHF / HF digital transmission system, used by many commercial/civilian aircraft and business jets, can be compared to "email for airplanes," as the registration of each aircraft is it's unique address in the system just like the call signs of an amateur radio operator. ARINC computers to the proper company, eliminating some of the routine voice communication with the company rout traffic. With ACARS, such routine items as departure reports, passenger loads, arrival reports, fuel data, engine performance data, and much more can be requested by the company and retrieved from the aircraft at automatic intervals. Before ACARS, flight crews had to use voice communications to relay this data to their companies on the ground.

Many commercial aircraft to automatically report wind and temperature data that can be extremely useful in weather research and forecasting also use ACARS. ACARS has been used for many years in research and modeling (it is currently used in the Rapid Update Cycle), but has only recently been made available to National Weather Service meteorologists in forecast offices.

Because ACARS data is often available at places far from radiosonde sites, and at asynoptic times, it can be very useful in forecasting connective weather and other phenomena. Aircraft near airline "hub" airports (such as Chicago O'Hare) sometimes transmit soundings of wind and temperature every 15-30 minutes during the busiest times of the day. The availability of frequent soundings allows the forecaster to monitor the degree of instability and wind shear throughout the day, and issue improved forecasts of connective initiation, severity, and dissipation.

Meteorologists at the NWS office in Chicago used ACARS data May 5,1997 to monitor the destabilization of the atmosphere, and to forecast the time of convective initiation and type of severe weather. ACARS and surface dewpoint were used early in the morning to forecast the convective temperature, which helped forecasters determine when surface-based convection was likely to develop. ACARS soundings were then used throughout the day to show the lifting and erosion of the low-level inversion, the destabilization of the atmosphere, and the directional and speed shear of the wind. The soundings were also transmitted to the Storm Prediction Center in Norman, Oklahoma, who found it useful in the decision to issue a Severe Thunderstorm Watch.

Meteorological data from certain commercial jet aircraft is provided by several airlines and airfreight companies (United, Northwest, Delta, and UPS), and is transmitted by ARINC (Aeronautical Radio Inc.) to the National Centers for Environmental Prediction (NCEP), the Forecast Systems Laboratory (FSL), and a few other users via ACARS (ARINC Communications, Addressing and Reporting System). FSL makes this information available to the NWS and certain other users via an Internet web page that allows display of wind plots, soundings, and alphanumeric data.

Several studies have compared ACARS with other data sources. Among these, Lord, et.al. (1984) compared ACARS flight-level winds with radiosonde, cloud-motion and VAS thermally derived winds. When ACARS was...

More recently, Schwartz and Benjamin (1995) compared ACARS ascent/descent winds and temperatures with radiosondes and found temperature differences were less than 2C on 94% of all occasions, and less than 1C better than 68% of the time. Wind speed RMS deviations were 4.1m/s while direction RMS differences were 35 degrees (mostly due to light and variable wind situations).
The FSL ACARS site has many quality control checks. Data failing any of the several tests is color-coded on the various graphic presentations, while more specific information is included with the alphanumeric data. While much of the quality control function is automated, some manual intervention is needed (Moninger 1997, personal communication).

ACARS data can be extremely useful in many weather situations. The NWS Chicago forecast staff has used it over the past several years to forecast low-level wind shear, fog, the precipitation type of winter storms, and convective storms such as this. Another account of how ACARS can be used to monitor the atmosphere in severe weather situations is detailed in Mamrosh and Labas (1996)

Although ACARS data is currently available only from jet aircraft near large and medium cities, there is an aggressive effort by the NWS to get more ACARS data. It is expected that ACARS data will be available from commuter aircraft that fly to small cities sometime in the future. In addition, there are a few UPS aircraft with a water vapor sensor. Soundings with dewpoints are available from these aircraft. The NWS has an agreement with UPS to install this sensor on sixty more aircraft in 1998 (Fleming 1997, personal communication). (Mamrosh)

Data does not simply comprise of text messages (although the request for tickets and shower facility at airport terminals has been noted). A series of sensors on the aircraft automatically collate information from the management unit and control units, these relate to height, speed, outside temperature, wind, fuel, engine performance etc., this information being transmitted by ACARS along with general positional data and more.

The ACARS data is processed into packets of serial data for efficient handling. The transceiver on-board the aircraft checks the frequency before transmission to ensure that it is clear then produces the short burst of data lasting less than one second.

Transmission takes place from air to ground (downlink) and from ground to air (uplink). A flurry of data may be passed at take-off and landing (termed DEMAND MODE as it is triggered by events) but positional transmissions may only occur occasionally, up to an hour apart so it is best to catch transmissions close to a major airport or flight paths to and from. General transmissions during flight (such as weather reports) may not be specifically acknowledged at the time of transmission (to minimise congestion) but reception will be acknowledged when the next transmission occurs.

ACARS messages are very structured. Each position in the message has a specific function. The address field identifies the aircraft with which the ground station is communicating. For the uplink (ground to air) messages it will be either the aircraft's official registration mark or the flight number of the service operating the aircraft. For downlinks (air to ground) messages it must always be the aircraft's official registration mark. By international agreement, the official registration marks are coded according to a county of origin one or two letter ICAO prefix. The single letter "N" is the prefix for all American aircraft. Other prefixes include: "C" for Canada, "G" for Great Britain, "F" for France, etc.

Nowadays, due to the high increase in the technologically wonderful world, a person can track a plane via the ACARS while sitting at home on a PC via the Internet. Technology allows us to tap into the radio signals into the backbone of the internetic cybernetic world and hereby allowing us to view the positions and the information specified by the plane. This information or data has some specific code in which it is transmitted. This has to be decoded in order for it to be understood. Here is some enlightenment into the language of the ACARS.

For ACARS purposes, the Address field must be seven characters in length and is always right-justified. If the aircraft's identification is less than seven characters, it must be left-filled with periods. Valid examples: N1825TU.C-FDCA.D-ABXR

ARINC has defined a series of two character message labels that identify message type. Many airlines have also defined their own sets of labels for company operation purposes.

The Downlink Block Identifier is used primarily as a means…