What is ACARS?

It has been over two years since Malaysian Airlines flight 370 went missing and the location of the aircraft has still not been determined.

There has been a lot of talk in the press about “ACARS” and that this was turned off and that the 01:37 transmission was never received. So what actually is this, what does it look like?

ACARS, or to give it it’s full name, Aircraft Communications Addressing, and Reporting System has been around since 1978. It was developed by a company called ARINC.

Before ACARS voice was used to send information to and from an aircraft – often by using dedicated radio operators!

Voice Radio Transmissions

ACARS replaced the voice radio transmissions with electronic transmissions to and from the aircraft. It uses VHF radio signals that are received and sent by a global network of land based radio stations and satellites.

Since 1978 avionics and flight management systems have made huge advances. ACARS has tried to keep pace with this and supports ever increasing types of data. Examples are weather, flight plans, technical information on the aircraft, information on aircraft components such as engines, and for communications between the flight crew and ground support teams.

We thought it would be interesting to show some real life example of ACARS transmissions.

All of these messages are outbound from the aircraft:

ACARS Message 1

G-DBCC BA088J #CFBWRN/WN14021208290022000006AUTO FLT FAC 2 FAULT
The first part identifies the aircraft as registration number G-DBCC, it’s callsign for this flight is BA088J
The next part is the ACARS data – in this case, the aircraft is reporting a fault

ACARS Message 2

N673UA UA0985 #M1BPOSN51210W001338,BEDEK,082231,140,NIGIT,082458,D273L,M19,24058,225,/TS082231,120214798E
This ACARS message is a position report from United Airlines Flight UA985

ACARS Message 3

EI-DTE XM0229 3401 ETA    0229/12 EGLL/LIML .EI-DTE/ETA 0915/FOB 0051
Estimated Time of Arrival report

ACARS Message 4

N657UA UA0909 /71 ORDAMS 0\READING LIGHT AT 19CEHWILL NOT TURN OFF
A faulty reading light being is being reported back to base from another United flight

ACARS Message 5

N832MH DL0142 110530 KDTW EDDF6A      OTHER THAN A BAD BACK…THE CONTROLLER HAS NOCOMPLAINTS THIS MORN…
Hmm – looks like a faulty Air Traffic Controller! Reported by a Delta flight this time

ACARS Message 6

N12114 CO0070 1EHAM REQUEST GATE ASSIGNMENT ETA0447
This is a gate assignment request so the crew knows what is going on. N12114 is a Boeing 757 operated by United Airlines.

Real Time Flight Tracking

The main problem with ACARS, at least when it comes to tracking flights, is that it was never designed to provide real-time flight tracking.

That was the job of radar and more recently ADS-B too. ACARS does help to track aircraft when out or range of these systems but the reports are sporadic and do not often include positional data.

In the future, ACARS will be replaced by more modern systems including data over the internet but for the coming years, it will still play an important role in the management of aircraft across the globe.