While flight plan calculations are necessary for safety and regulatory compliance, they also provide airlines with an opportunity for cost optimization. Effective Flight Plans Can Help Airlines Economize

By Steve Altus, Ph.D., Senior Scientist, Airline Operations Product Development, Jeppesen

Every commercial airline flight begins with a flight plan. Over time, small adjustments to each flight plan can add up to substantial savings across a fleet. Optimal overall performance is influenced by many factors, including dynamic route optimization, accurate flight plans, optimal use of redispatch, and dynamic airborne replanning. While all airlines use computerized flight planning systems, investing in a higher-end system — and in the effort to use it to its full capability — has significant impact on both profitability and the environment.

An operational flight plan is required to This article provides a brief overview of and lost revenue from payload that can’t ensure an airplane meets all of the flight planning and discusses ways that flight be carried. These variations are subject to operational regulations for a specific flight, planning systems can be used to reduce airplane performance, weather, allowed to give the flight crew information to help operational costs and help the environment. route and altitude structure, schedule them conduct the flight safely, and to constraints, and operational constraints. coordinate with air traffic control (ATC). Flight planning fundamentals Computerized systems for calculating Optimizing flight plans flight plans have been widely used for A flight plan includes the route the crew will decades, but not all systems are the fly and specifies altitudes and speeds.I t also While flight plan calculations are necessary same. There are advantages to selecting provides calculations for how much fuel the for safety and regulatory compliance, they a more capable system and using all of airplane will use and the additional fuel it also provide airlines with an opportunity for its analytical and optimization capabilities. will need to carry to meet various require­ cost optimization by enabling them to deter­ Using the flight planning process to reduce ments for safety (see fig. 1). mine the optimal route, altitudes, speeds, fuel not only saves money but also helps By varying the route (i.e., ground track), and amount of fuel to load on an airplane. the environment: carbon dioxide (CO2) altitudes, speeds, and amount of departure Optimization can be challenging emissions are directly proportional to fuel fuel, an effective flight plan can reduce fuel because it involves a number of different burn, with more than 20 pounds of CO2 costs, time-based costs, overflight costs, elements. An optimized flight plan must not emitted per U.S. gallon of fuel burned. 27 WWW.boeing.com/commercial/aeromagazine Figure 1: Minimum information on an operational flight plan By varying the parameters in a flight plan, flight planning systems can improve the efficiency of an airline’s operations.

COMPUTER FLIGHT PLAN SPEED SKD CLB-250/340/.84 CRZ-CI40 1 DSC-.84/320/250

FUEL TIME POA ZBAA 2 224000 10/31 ALT ZBTJ 006100 00/15 1 What speed to fly (possibly varying along RESV 008500 00/30 the route) CONT 011200 00/40 2 How much fuel the airplane will burn REQ 249800 11/56 (“trip fuel”) XTR 000000 00/00 TOT 3 249800 11/56 3 Total departure fuel, and how it is allocated – fuel to alternate, contingency fuel, and other KSEA..YVR J528 TRENA J488 UAB..YYD NCA34 YXY J515 FAI J502 OTZ B244 allocations that vary between airlines and FRENK G902 ASBAT B337 URABI G212 DABMA W74 SABEM G332 GITUM GIT01A ZBAA 4 regulatory rules 4 What route (ground track) to fly FL 300/YVR 320/YYD 340/FRENK 348/BUMAT 381 5 5 What profile (altitudes along the route) to fly

only take into account the correct physics Route Optimization that used fixed company routes in its (i.e., airplane performance and weather) computer flight planning system. This but also route restrictions from ATC and The best route to fly depends on the actual airline, which had 60 single-aisle airplanes, all relevant regulatory restrictions. The conditions for each flight. These include the used fixed routes developed with historical mathematical nature of these constraints forecast upper air winds and temperatures, winds and experience about ATC require­ and the overall size of the calculation the amount of payload, and the time-based ments. The study determined that using combine to make it a challenging problem, costs that day. The time-based costs are routes optimized with the most recent even by modern optimization standards. especially dynamic, driven by the value forecast winds, with numerical constraints Some of the equations that describe the of the payload and the schedule and modeling ATC requirements, would save behavior are nonlinear and noncontinuous, operational constraints for the crew and about 1 million U.S. gallons of fuel per year. and the airplane state is dynamic (i.e., it the airplane. Winds can have a significant This, in turn, would reduce annual CO2 depends on how the airplane has gotten impact on the optimal route: it can be very emissions by about 20 million pounds. to a specific point, not just where it is). As far from the great circle “direct” route (see a result, tens to hundreds of thousands of fig. 3). Flight planning systems use wind The importance of accuracy individual calculations are required for a forecasts from the U.S. National Weather single flight. Service and U.K. Meteorological Office, Airlines can reduce fuel consumption and An optimal flight planning scenario for updated every one to six hours, to include costs by improving the accuracy of their saving fuel and emissions involves calculat­ the winds in every flight plan calculation. flight plans. The flight crew and dispatcher ing multiple routes or operating approaches While nearly all computer flight planning can elect to add fuel they think might be for each flight, ranking these scenarios by systems can optimize routes, many airlines needed to complete the flight as planned. total cost, choosing the scenario that best still use fixed “company routes” most of the But the heavier the airplane, the more fuel it accomplishes the airline’s cost objectives, time. One reason adoption of dynamic will burn, so adding extra fuel — which and providing summaries of the other route optimization has been limited is that adds weight — burns more fuel, increasing scenarios for operational flexibility (see ATC organizations, overflight permissions, both operating costs and emissions. fig. 2). While the scenario chosen by the and company policies place restrictions on Accurate flight plan calculations can system might be used most of the time, routing­ in certain areas. An effective flight minimize the additional fuel the flight crew dispatchers and operations managers at an planning system contains models of all adds. Accurate calculations are the result airline’s control center may choose another these restric­tions, which are then applied of several factors that combine engineering scenario to meet the airline’s operational as constraints in the numerical optimization and information management. Some of the goals, such as routing of airplanes, crews, process. This allows the flight plan to be relevant factors require integration with and passengers. Because they are often optimized with the dynamic data on winds, other systems and data sources, both making these decisions shortly before temperatures, and costs while still within and outside an airline. departure time, a user-friendly presentation complying with all restrictions. For example, the basic airplane perfor­ of the relevant information is vital. One recent study by Boeing subsidiary mance characteristics come directly from Jeppesen considered the benefit of manufacturer data, but must be modified dynamic route optimization on an airline 28 aero quarterly qtr_03 | 09 Figure 2: Optimal flight planning using multiple routes for each flight A user interface allows management of multiple possible scenarios for a single flight.

1 2 3 4

1 Multiple routing scenarios displayed simultaneously 2 Scenario sort by fuel 3 Scenario sort by payload 4 Scenario sort by any computed field

by active master minimum equipment­ list/ defined by a percentage of flight time or An advanced flight planning system can configuration deviation list data (available in planned fuel burn (varying by different reoptimize the flight plan while the airplane an operator’s maintenance tracking sys­tem) regulators), can be reduced by splitting a is in flight. The airline’s operations center and by measured devia­tions from base­line flight plan into two different calculations: has more information about weather and data, available from Boeing Airplane Perfor­ one from the departure airport to an airport traffic far ahead of the airplane, as well as mance Monitoring software. Up-to-the-minute that is closer than the intended destination, the dynamic costs associated with other payload predictions require integration with and another from a decision point on the flights (related to crew, airplane, and the reservation system, and time-based route of flight to the planned destination. passenger connections), so the flight cost prediction is most accurate when it is Each calculation requires contingency fuel planning system can find better solutions integrated with operational control and crew over its entire distance, but each is less than the flight crew working with the flight tracking systems. Integration with convec­ than the total that would be required for the management computer (FMC) alone. The tive weather and air traffic delay pre­dictions entire flight to the planned destination. The new route and latest forecast winds can be helps to accurately predict possible air­borne actual flight must carry the greater of the uplinked directly to the FMC, minimizing delays or deviations, rather than using rough contingency fuels for the two scenarios. crew workload. guesses. Because an inte­grated, properly The optimal flight plan places the tuned flight planning system increases the decision point in a location where the Trends in flight planning accuracy of calculations used to develop contingency fuels for the two scenarios are flight plans, flight crews and dispatchers will exactly equal; moving it in either direction Airspace design and regulations are chang­ feel confident reducing the amount of extra increases the fuel required for one scenario ing all the time, sometimes quite rapidly. fuel they request. or the other. While some general guidelines Some recent innovations include continuous Further study of the airline described in exist for a good location of the decision descent approaches, high-altitude redesign the “Route Optimization” section found that point, a flight planning system can calculate in the western United States, and new U.S. it carried an average of 300 U.S. gallons of the optimal location automatically — and it Federal Aviation Administration (FAA) extra fuel per flight. Analysis showed that can vary dramatically based on the relative extended-range twin-engine operational the airline could save an additional million locations of all the airports (see fig. 4). performance standards (ETOPS) rules. U.S. gallons of fuel per year by cutting that (Boeing can help operators make sure amount in half. Dynamic Airborne Replanning they’re defining all of theirETOP S parame­ ters and fuel analyses correctly.) These are in Optimal Redispatch Decision Point Winds, temperature, convective weather, addition to less recent changes, such as the and ATC congestion have a sizeable introduction of a reduced vertical separation Another way to decrease total fuel carried impact on the optimal 4D path for an minimum in different parts of the world. is to reduce international contingency fuel airplane. Over the course of a long flight, However, not all operators can take required by using a redispatch technique. this information can change significantly, advantage of the improvements right away Contingency fuel (called “international and the predeparture flight plan may no because their flight planning software can­ reserve fuel” in the United States), which is longer be optimal. not be updated quickly enough. Those whose

29 WWW.boeing.com/commercial/aeromagazine Figure 4: Determining the optimal redispatch decision point On this flight from Denver to Tokyo, the optimal decision point to redispatch changes based on the relative location of all the airports. In this first instance, the decision to turn back to Anchorage is made after the airplane is over Russia. In the Anchorage second instance, the redispatch decision point occurs as the airplane approaches the coast of Japan. The diversion city is Sapporo. Optimum decision point for Anchorage Diversion Path

Diversion Cities

Sapporo Optimum decision point for Sapporo

Denver Tokyo

Figure 3: Forecast winds must be software is ready could take full advantage cost, however, is not independent for a considered to find the optimal route of the innovations, immediately reducing single flight, but related to the decisions This flight from Jakarta to Honolulu illustrates their fuel consumption and operating costs. made for all an airline’s flights because the that a wind-optimal flight path may be far Further route, altitude, and speed cost for passengers, crew, and the airplane from the great circle. This route is 11 percent optimi­za­tion will be made possible by 4D itself to arrive at a specific time depends on longer than a great circle route, but is 2 percent faster and uses 3 percent less fuel. trajectory-based approaches, such as the when their next flights will depart — which, Next Generation Air Transportation System, in turn, depends on when all other flights which is the FAA’s plan to modernize the arrive. By combining the different operational national airspace system through 2025, decisions and optimizing them together, and the Single European Sky Air Traffic better solutions that factor in all of the dif­ Manage­ment Research Programme fer­ent costs and constraints can be attained. (SESAR). Ongoing research goes beyond compliance with new approaches, Summary identifying oppor­tunities for improved optimization that build on the changes to Accurate, optimized flight plans can save Honolulu the global traffic management system. airlines millions of gallons of fuel every Companies such as Jeppesen are also year — without forcing the airlines to com­ working on improved optimization scenar­ promise their schedules or service. Airlines Jakarta ios designed to minimize fuel consumption, can realize their benefits by investing in operational cost, and emissions. For a higher-end flight planning system with instance, Jeppesen is developing a new advanced optimization capabilities and optimization objective function for its then ensuring accuracy by comparing flight flight planning system that is based on an plan values to actual flight data, identifying atmospheric impact metric developed by the cause of discrepancies, and using this airplane design researchers at Stanford Optimized Route information to update the parameters used Great Circle University, taking many emission products in the flight plan calculation. into account, rather than just minimizing Current research in flight planning fuel as a means to minimize CO2. system development ensures that flight Another future trend in flight planning planning systems take full advantage optimization is a close integration with of airspace and air traffic management other airplane operations efforts, such as liberalization and work together with other disruption recovery, integrated operations airline operations systems to produce the control, and collaborative air traffic man­ best overall solutions. agement. Current systems can already pick For more information, please contact optimal cost index speeds if the cost of Steve Altus at [email protected]. arriving at different times is available. This 30 aero quarterly qtr_03 | 09