What is Attila™?
Attila is a company-managed arrival sequencing system, designed to improve the efficiency and profitability of the daily operation. Unlike other systems, Attila calculates a system wide optimum for the entire arrival flow rather than an individual aircraft. Attila's goal is to provide a more beneficial solution for the company as whole.
As an example of a system benefit, as proven in Delta's ongoing ATL Attila operation, the Terminal Area Dwell Time (time from the arrival cornerpost to landing) for all aircraft is reduced by approximately one minute. This means that even if you are not able to make your individual RTA, your flight still benefits from the fact that other pilots were able to make their RTA. Of course, the more often you can make the RTA, the better the system will work.
As one pilot stated, "When I receive the Attila message, I am able to comply 70% to 80% of the time, and the more messages I receive, the better I get at meeting the Attila goal". In the current implementation, meeting the Attila RTA 70% of the time is considered very successful.
Given the amount of change allowed by company policy, some controller actions and intervention will still be required. ATC will continue to do what it does today, maintain the safe separation of the aircraft. Attila will make this easier for the controllers and more profitable for the airlines.
Company flight #123 is predicted to arrive at the corner post at 12:10Z. This flight is 7 minutes ahead of schedule.
It is an MD-88 flying at M.78.
Company flight #321 is predicted to arrive at the corner post at 12:11Z. This flight is 15 minutes behind schedule. It is also an
MD-88 flying at about M.76.
Attila calculates a system solution about 1 to 2 hours out. As part of this solution Attila sends an ACARS message that requests Flight 123 to adjust their corner post arrival time to 12:12Z by slowing down. Attila requests Flight 321 to adjust their corner post arrival time to 12:09Z by speeding up.
Note that neither change may be perceived as a "good thing" to each individual aircraft. Flight 123 may allow other company or even non-company aircraft to pass. Flight 321 will speed up and burn more fuel. However, even in this simple example, it's easy to see that the fuel spent was offset by the fuel saved in slowing one aircraft down, Flight 123 is still on schedule A0 and Flight 321 has now moved from being a late statistic to on schedule A15.
Rules of the Road
Although Attila works independently of the Air Traffic Control system, it is designed to be completely compatible with it. To ensure this compatibility, there are certain "rules of the road" that are very simple and very important to the success of the program:
- Always disregard Attila for any ATC instructions. Once an ATC instruction has been received (a vector or a speed change, or any other changes) simply disregard Attila and follow ATC instructions. There is no need to report this. Attila is monitoring the flight continuously and will know immediately if you are unable to comply for any reason.
- Do not use the ATC frequency to talk about Attila times or priorities. This will not only unnecessarily increase the chatter on the ATC frequency, ATC controllers will not be able to answer questions about the Attila program. Instead, please direct all questions or problems to company dispatch.
- Attila messages will request a speed change of up to 2 minutes or 16 kts (about .03 mach), whichever is less. The Aeronautical Information Manual (2/19/2004) states: "notify ATC for a "Change in the average true airspeed (at cruising altitude) when it varies by 5 percent or 10 knots (whichever is greater) from that filed in the flight plan". All Attila changes should be within this guideline.
- If the pilot receives a direct routing from ATC after receiving an Attila message, maintain the last computed speed, i.e., do not slow down to make the Attila RTA. This will usually indicate that the controller has identified a potential benefit in direct routing and allow the Attila queue to collapse forward in time. Attila will note it and plan around it.
- As the pilot approaches the airport (within 200 to 300 NM), the ATC controller may begin to provide speed restrictions or in-trail vectors (i.e., arrival metering or in trail with another aircraft). The fact is that, with Attila, the speed changes and vectoring will be less. Once this happens, please disregard the Attila corner post time.
- Report problems to dispatch. Like all sophisticated computer systems, there is the possibility of Attila generating a time that falls outside the guideline. This could be due to bad input data, a software logic error, or even an avionics error. If this happens, please disregard the Attila message and report the error. As much information as is easily available would be helpful (like time received, what the error was, current estimate etc.), however, it is important to know there was a problem even if you don't have the related data. This allows us to find the problem and correct.
- Although it is important from a profitability viewpoint to try to make the Attila time, if for any reason you are uncomfortable with the Attila corner post time, simple disregard. As is always the case, before altering speed based on an Attila message, the pilot should evaluate fuel, time distance, weather, etc., to assure a safe operation. Again, there is no need to report this.
Time Based Navigation Techniques
An FMS aircraft will obviously have an easier time meeting the Attila RTA. But even with a non-FMS aircraft, the company's flight plans are accurate and can be used to calculate the ground speed change necessary to meet the Attila time. Suggested techniques to meet the Attila time include:
- FMS Crosscheck - While the FMS is usually very accurate, there are times when the FMS cornerpost time is different than the Attila cornerpost time. Therefore, if the speed change required by the Attila message seems excessive, the first step should be to crosscheck the FMS calculation. After assuring the winds are entered correctly, simply go to the PROG page and replace the Destination with the target cornerpost fix. The FMS will then show distance (on the FMS routing) and time to the target cornerpost. Then divide the distance to the cornerpost by the groundspeed in nautical mile per minute. For example, if the FMS shows 624 NM to the target cornerpost, and the groundspeed is 480 kts (8 NM/minute), it will take 78 minutes to reach the cornerpost. Absence any large wind changes (usually visible on the Flight Plan), the aircraft will reach the cornerpost 78 minutes later.
- Directs - If the pilot receives a direct prior to receiving the Attila RTA, the FMS may, or may not, compute abeam points. If the FMS does not calculate abeam points (with the entered winds), the FMS cornerpost prediction could be inaccurate. Please assure that there is adequate abeam points and wind data on your route to increase the accuracy of the FMS cornerpost time calculation.
- FMS RTA - When using the RTA function in some FMS, it only alters the aircraft speed during the cruise phase of flight, and not in the descent phase of flight. If this is the case, given that the cornerpost is usually well into the descent, it limits the time the FMS has to meet the RTA and the FMS may calculate a higher than anticipated speed change. To minimize this effect, once the pilot receives the Attila RTA, adjust the Cost index (which effects cruise and descent speeds) so that the calculated cornerpost time in the FMS is close to the Attila RTA. Once this is done, the pilot can then input the RTA in the FMS to refine the enroute speed change to more accurately meet the Attila RTA.
- Speed Adjustments - a .01 change in mach equals 5 to 6 knots of TAS. To gain 1 minute over 1 hour, will require an increase from .76 mach to .775 mach. To gain 2 minutes - will require an increase from .76 mach to approximately .79 mach. For a given mach number above the IAS to mach climb cross over point (narrow body FL 250, wide body FL 270), climbing decreases TAS, while descending increases TAS.
- Climb/Descent - For a fixed mach, a 2,000 foot change in altitude changes the TAS by approximately 5 kts. For example, if you hold .75 mach, climbing from FL330 to FL370 will decrease TAS by 10 knots. Make sure to check winds at both altitudes.
- FMS Aircraft - Enter winds, crossing restrictions and descent speeds. Enter corner post and Attila time on the RTA page. For non-RTA aircraft, adjust speed such that the FMS fix time equals the Attila time. Fine tune as necessary.
- Non FMS Aircraft - Make initial speed adjustment using the flight plan. For example, after takeoff, the pilot does the time computation on the flight plan and sees that they would arrive at the corner post at 1737Z. Approximately 1.5 hours from the corner post, they receive an Attila suggested corner post time of 1735Z. Assuming that there is 1 fix halfway between the aircraft and the corner post, the pilot would need to increase speed so as to arrive at the first fix 1 minute ahead of flight plan. This speed would then put the aircraft 2 minutes ahead of flight plan at the corner post.
- Another non-FMS 4D tool is groundspeed management. Using the FMS or flight plan groundspeed of 480 kts (8 NM per minute), to make up 2 minutes 1 hour prior to the corner post, the pilot must increase speed by 16 kts TAS (8NM/min x 2 minutes/1 hour). If the pilot had to lose 3 minutes 2 hours from the corner post, they would have to slow by 16 kts TAS (8NM/min x -4 minutes/2 hours).
- Time/Distance - Once within DME range of an arrival VOR, calculate the distance to the corner post and divide by the groundspeed (NM/min) to find minutes remaining to the corner post. Fine tune speed as necessary.
Attila is a proven and innovative way for airlines to manage their aircraft. Attila offers airlines and its employees an opportunity to move ahead of the competition. We appreciate all of your help in making this program successful.
Attila is a Trademark of ATH Group. Copyright © 1998-2015 ATH Group, Inc. All rights reserved. Protected by US and International Patents