This paper is intended to provide an operator's view of the impact of GPS on the air transport industry. The discussion centres on use of GPS for the en-route, oceanic, terminal area and precision approach phases of flight. In summary the author suggests the following:

(i) Inefficient use of airspace is costing the airlines a huge amount of money. However, GPS is not a pre-requisite of a move towards more efficient use of that airspace, although it will be required as part of the eventual CNS/ATM package. In the near term, better usage of current equipment such as IRS and DME, together with the introduction of ADS can provide the required level of accuracy for reduced separation in en-route and oceanic airspace.

(ii) There is a real need to provide navigation for non-precision approach worldwide, independent of ground-based infrastructure. This is the area in which GPS can provide the most immediate improvement to safety.

(iii) There are still a large number of questions hanging over GPS for precision approach. This leads the author to believe that it will not be capable of replacing ILS for the more critical Cat 2 and 3 applications quickly enough to avoid the loss of these capabilities in some critical locations. For this reason, it is postulated that MLS will be required in Europe, at least. Even if MLS is not required, there will still need to be a means of dealing with the transition away from ILS and for this reason the concept of a multi-mode receiver has been developed.

A realistic runway capacity study for two major airports, namely Frankfurt (EDDF) and Chicago O'Hare (ORD) is presented, assessing the effect of optimal scheduling on the runway capacity and air traffic delays. The maximum position shift (MPS) runway scheduling algorithm, used in the study, was developed by Trivizas at the Massachusetts Institute of Technology (1987).

EDDF is studied in the context of 160 major European airports, with a real traffic sample from 6 July, 1990. ORD is studied in the context of 26 major US airports using a large traffic sample from 1 March, 1989. Secondary airport traffic has been assigned to the geographically nearest major hub and time compression has been used to extrapolate to an artificially denser scenario.

The results show that optimal scheduling can bring about capacity improvements of the order of 20 percent, which in turn reduce delays up to 70 percent. These results are the product of a dynamic traffic management process which has been visually validated by observing animated runway operations and monitor functions.

The study has been conducted with TMSIM, a comprehensive, object-oriented simulation tool that allows one to build an understanding of the structure and functionality of the air traffic control system, by modelling its components, their functionality and interactions, and measuring component and system performance. It features interactive route network editing (using menu/mouse techniques), complete route and airport structure modelling, independent flight and ATC objects, 3-D animation, advanced algorithms for scheduling, routeing, flow management, airspace restructuring (sectorization) and performance (capacity and communications workload) analysis.