Cruise Fuel Reduction Potential from Altitude and Speed Optimization in Global Airline Operations

Luke Jensen; Henry Tran; R.  John Hansman

This paper examines the potential fuel efficiency benefits of cruise altitude and speed optimization using historical fight path records. Results are presented for a subset of domestic US flights in 2012 as well as for long haul flights tracked by the European IAGOS atmospheric research program between 2010 and 2013. For a given lateral flight route, there exists an optimal combination of altitude and speed. Analysis of 217,000 flights in domestic US airspace has shown average potential savings of up to 1.96% for altitude optimization or 1.93% for speed optimization. International flights may be subject to different airline and/or air traffic management procedures and constraints. Examination of 3,478 long-haul flights, representing three airlines and a single aircraft type over a four-year period, indicates average potential savings of up to 0.87% for altitude optimization or 1.81% for speed optimization. This is equivalent to a mean fuel savings of 905 pounds and 1981 pounds per flight, respectively. Due to the limited sample set for long haul flight records, conclusions from this stage of the international study are limited to the specific airlines and aircraft types included in the IAGOS measurement program. I. BACKGROUND Environmental and economic concerns provide motivation for fuel consumption reduction in air transportation. There are various techniques to control fuel-related environmental impact with varying implementation timelines and potential benefits. These include new aircraft technology (decade-scale implementation, high cost), retrofits to existing aircraft (multi-year implementation, medium cost), alternative jet fuel and propulsion technology (decade-scale implementation, high cost), and operational mitigation (rapid implementation, low cost) [1]. Operational mitigations are useful due to the potential for rapid implementation and low capital expenditure, although the long-term benefit is generally less than other technology-driven solutions. Prior research in academia and industry has identified potential operational mitigations. For example, Marais et al. proposed 61 specific operational mitigations with implementation timelines in the 5-10 year range [2]. Of these, eight mitigations dealt with opportunities in cruise altitude and speed optimization (CASO). The fuel efficiency of an aircraft at any point along its flight path is a function of weight, altitude, speed, wind, temperature, and other second-order effects. At a fixed weight, there exists a combination of speed and altitude at which instantaneous fuel efficiency is maximized, as shown in Figure 1 for a typical widebody long-range airliner. For a full flight, this becomes an optimal sequence of speeds and altitudes to minimize fuel consumption [3]. The speed and altitude at which aircraft are actually flown may differ from this optimal point for a variety of operational and practical reasons. Integrated fuel consumption depends on effective trajectory planning in speed and altitude as well as in lateral flight path. There are many examples in the literature demonstrating techniques and potential applications for single-flight trajectory optimization in lateral, vertical, and temporal dimensions (e.g. [4]–[11]). However, no research has demonstrated the systemwide benefits pool of such optimization concepts compared to current operating practices. The degree to which flights may operate at optimal altitudes and speeds depends on a variety of system characteristics, including prevailing weather conditions, congestion, airline schedules, operating costs, and Air Traffic Management (ATM) technologies available on the ground and in the cockpit of participating aircraft. In domestic US operations, the suite of communication, navigation, and surveillance (CNS) technologies allows for continuous very-high frequency (VHF) radio communication, and radio-based navigation, and radar tracking. However, traffic volumes prevent unconstrained altitude selection in most areas of the country. Speed selection is driven by a combination of ATM constraints and airline operational priorities. Figure 1. Instantaneous fuel efficiency of a typical long-haul aircraft at a fixed weight (calm winds, standard atmosphere) *

Cruise Fuel Reduction Potential from Altitude and Speed Optimization in Global Airline Operations

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