1.0 Introduction

1.1 Purpose of the Current program
The ultimate objective of this effort is to develop an airborne strategic flight replanning concept (during block to block operations, versus pre-flight) that enables maximum aircraft and airline efficiency for commercial aircraft in a future Free Flight environment, including consideration of constraints on the flight path that may be imposed by congested airspace, traffic flow into terminal areas, airline scheduling and fleet requirements, weather, special use airspace (SUA), traffic, terrain, and others. Free Flight is an envisioned paradigm-shift in the way air traffic management is performed, intended to reduce operational inefficiencies, and with implications for how strategic flight replanning is done on the flight deck. However, the emphasis of the airborne flight replanning concept developed here is on reducing routing inefficiencies, not on Free Flight per se. The general strategy, therefore, is to describe and analyze flight planning and replanning in today’s environment, particularly in regard to current inefficiencies. Based on these analyses, an airborne flight replanning concept will be formulated; it may contribute to implementation of Free Flight, and it may help reduce inefficiencies independent of Free Flight. The concept will include description of replanning function allocation between ground personnel (AOC, ATC) and flight crew, flight deck replanning information requirements and information flow to support the airborne replanning concept, and will touch on other flight deck issues such as human-automation function allocation, flight crew interfaces, and integration of the concept with existing flight deck functionality. Since this is a problem-driven approach, we will first review the operational inefficiencies.

1.2 Inefficiencies Addressed
The overriding concern of the AATT program is capacity problems within the National Airspace System (NAS) and worldwide. Capacity limitations stifle future traffic growth, and cause inefficiencies in current operations. Routing inefficiencies, some capacity-related and some not, include delays and diversions, and excessive fuel burn due to indirect routing. These problems are not evenly distributed within the system; the problems are more acute in high density traffic areas (e.g., east coast and below 35000 ft), high volume terminal areas (e.g., Chicago), and on “bad flying” days (e.g., extensive weather systems, low visibility). The largest capacity bottleneck is the combination of high traffic airports and IFR conditions, and while more efficient routing is necessary, it is not sufficient to solve this problem. Hence we believe that touting capacity improvements as the main objective of the airborne strategic replanning concept addressed here is ill-advised. We can, however, do much to benefit airline operations if we can mitigate the inefficiencies that have root causes in the current system of flight planning and replanning.
A recent analysis (Chew, 1997) states that the primary product of an airline is its schedule and the primary operational goal of the airline is to maintain schedule integrity. Chew indicates that airlines view the critical operational problems facing scheduled airlines today to be (1) delays and (2) route and altitude inefficiencies. Delays are far and away the most critical problem because they jeopardize schedule integrity. Better flight planning and replanning may help reduce these significant airline operational inefficiencies.
　
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