What is ACARS?

ACARS (Aircraft Communication Addressing and Reporting System) is a digital data link system transmitted in VHF range (118 MHz to 136 MHz). ACARS provides a means by which aircraft operators can exchange the data with an aircraft without human intervention.  This makes it possible for an airline to communicate with the aircraft with their fleet in much the same way as it is possible to exchange data using a land base digital network.

ACARS is still the only high-frequency data link service provider with global coverage. ACARS has over 300 airline users and 15,000 aircraft users around the world. ACARS uses VHF, HF radio and real-time satellite data provided by Inmarsat to communicate to a ground station with the help of a service provider.

ACARS communications are automatically directed to the ground base computers to the relevant aircraft operator.

On board sensors placed strategically around the aircraft provide the ACARS system with data and performance measurements, such as equipment status, satellite "ping" data, position reports and engine monitoring. ACARS gathers this data and automatically sends it back to the ground station.

Typical ACARS Messages Information 
Typical ACARS messages have routine information such as;

• passenger load 
• departure report
• arrival report 
• fuel data 
• engine performance data

ACARS use variety of hardware and software including those that are in Aircraft but also those which are on ground.

Types of ACARS Messages 

1. Downlink messages (originate from the aircraft) 
2. Uplink messages (originate from ground station) 

ACARS messages consist of ; 

• Mode identifier (e.g. E)
• Aircraft identifier (e.g. N27051)
• Message label (e.g. 5U- a weather request)
• block identifier (e.g. 4)
• message number (e.g. F00M) 
• flight number (e.g. BD01NZ) 
• message content 

Different Channels are used in the different part of the world. 

Frequency                     ACARS services 

129.125                  MHz USA and Canada (additional)

130.025                  MHz USA and Canada (secondary)

130.450                  MHz USA and Canada (additional)

131.125                  MHz USA (additional)

13 1.475                 MHz Japan (primary)

131.525                  MHz Europe (secondary)

13 1.550                 MHz USA, Canada, Australia (primary)

131.725                  MHz Europe (primary)

136.900                  MHz Europe (additional)