SAS Datalink System

Takeoff Data Calculation (TODC) over ACARS

By Björn Syrén, SAS

Fleet Type Acars TODC status
Boeing 737NG Operational 1998
Boeing 767 Operational 1999
Airbus A321 Operational May 2002
Airbus A340 Operational Aug 2002
Boeing MD-80 Operational Oct 2002
Airbus A330 Operational Feb 2003
Boeing MD-90 Operational May 2003
Dash-8-Q400 Operational July 2003
Avro RJ Operational
CRJ900 Operational Dec-2008

One of the most successful applications so far has been Takeoff Data Calculations (TODC). Before every takeoff, a performance calculation or check must be made in order to ensure that a safe takeoff can be made within regulated performance margins. This calculation must take into account  aircraft technical parameters and environmental parameters, including:

  • aircraft type and version

  • engine type and thrust rating

  • actual takeoff weight of the aircraft

  • status of aircraft systems that affect performance (wing and engine anti-ice, brakes, reversers etc)

  • actual airport, takeoff position, runway length and slope, obstacles during climbout etc

  • meteorological conditions (wind, temperature, QNH)

  • runway contamination eg water, slush, ice

Together these parameters result in the correct flap settings and takeoff speeds for the actual takeoff weight. If the aircraft is in fact not using the maximum possible takeoff weight, then engine thrust can be reduced in order to save wear on the engines.

The traditional way for pilots to obtain takeoff performance data was through paper tables (gross weight charts) carried onboard. The performance data in these charts had to be simplified and very conservative in order to fit into a manageable paper format. As a consequence the payloads and thrust settings obtained from these tables did not take advantage of the actual performance of the aircraft.

Computerizing the TODC calculations and using a sophisticated aircraft performance program allows much more precise calculations to be made. The net effect is that it enables higher payloads and reduced engine operating costs. The improvements can be significant.

One option is to make the TODC calculations using a laptop computer in the cockpit. This was not an attractive solution to SAS because of the logistical issues involved in supporting a relatively large fleet (180+ airplanes). Databases need to be updated regularly, the performance program may need unscheduled updates and on top of this we have issues with batteries or power supplies as well as broken or lost laptops.

SAS chose instead to implement TODC calculations via ACARS. This made it possible to use a powerful ground TODC application which is centralized, automated and capable of supporting the entire aircraft fleet with advanced takeoff performance calculations. It brought many advantages compared to the laptop computer solution. Updates to the airport database and performance program are quick and are instantly available to the entire fleet. The logistical issues are avoided.

Some pilots were initially skeptical to if Acars was capable of delivering the TODC information reliably and with acceptable delivery times. They were proved wrong. The typical end-to-end TODC transaction as seen from the cockpit is 15-25 seconds which is operationally acceptable and compares favorably with other solutions. Reliability has been excellent and is not an issue today.

In the aircraft we introduced an Acars TODC request function were the pilot enters the input data for the calculation. The downlink is sent to the ground TODC application, the calculation and optimization is made, and the uplink response is sent back to the cockpit. It can be printed if desired. If conditions change a new calculation can be made easily. The TODC output also gives the pilot a shortlist of alternative runways and takeoff positions which are possible under the circumstances.

Acars TODC is currently in service for the Boeing 737NG, Boeing 767 and Airbus A321 fleets. It is to be introduced for the Airbus A340, A330, Boeing MD-80 and Dash-8-Q400 fleets during 2002.

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Example Acars TODC request screen (above)

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Example Acars TODC printout (above)

Latest update: 25-Jan-2010
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