Feasibility Analysis and Fuel Burn Benefits of Relaxing Constraints in High Altitude Cruise

Abstract

Operational interventions, such as enabling more fuel-efficient trajectories, are desirable in mitigating the environmental impact of air travel due to their relatively fast implementation potential. In particular, the vertical inefficiency arising from the altitude stratification in the airspace can be mitigated by relaxing vertical constraints. The feasibility of vertical flexibility is evaluated by quantifying the rate of close encounters and the frequency of alerts that would be needed to prevent them. Substantial diurnal variability in the number of close encounters was found in the airspace, with lower rates of events during the nighttime period. Furthermore, regional differences among Air Route Traffic Control Centers were observed in the number of close encounters. The frequency of controller intervention events that would have to occur was evaluated at 25 NM and 50 NM alerting distance levels, and it was found that, given sufficient technological capabilities for alerting at the 25 NM reaction distance, most centers would have fewer than 10 alerts per hour during the nighttime period. Boston, Miami, and Seattle appeared especially promising, with approximately one alert per hour for each region. Finally, the potential fuel benefit from enabling vertically optimal trajectories was estimated to be up to 100,000 gallons of fuel savings per month in the case of a CONUS-wide nighttime implementation.