SAS Datalink System
Takeoff Data Calculation (TODC) over ACARS
By Björn Syrén, SAS
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:
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.
Example Acars TODC request screen (above)
Example Acars TODC printout (above)
| Latest update: 25-Jan-2010
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