British Airways currently operates over 200 aircraft and the fleet continues to grow. These include twelve airframe types coupled to fifteen engine types. They represent most of the design and build philosophies that have been used over the last thirty years.

The aircraft range from the turboprop 748s through the latest 747-400s to Concorde.

The one feature which is common to all these aircraft is that they are maintained to standards which are defined to ensure maximum passenger safety and the best financial returns.

Europe has a long tradition in the technical innovation and production of new advanced aeronautical concepts. However the talent to transfer these technical advances into a commercial success was missing. With the creation of Airbus Industrie and pooling of resources for a common product, the concept of a technically very advanced aircraft family which is competitive in the world market has been successfully applied. New technology remains a constant challenge and this paper describes the main axis of research and new technologies which are of interest for future application in civil transport aircraft. A general review is given of the main improvement potentials in aerodynamics, propulsion systems, airborne systems and new materials.

The scope of the air-ground data links, which have been developed over the last ten years to meet the airlines' operational requirements, will be extended in future years.

Air traffic control is one of the fields which will certainly make extensive use of this type of link. Indeed, it appears to be necessary to deal with the problem of traffic saturation globally by taking account of the navigation capabilities of modern aircraft as regards precision and the considerable automated flight/ground exchange possibilities which will be provided by future telecommunication networks.

The contents of the messages exchanged between aircraft and air traffic control centres, and the interfaces with the human operators concerned, i.e. pilots and controllers, must form the subject of thorough investigations conducted with all the parties involved: constructors, equipment manufacturers, traffic control organisations, and airlines. Aerospatiale have already taken this problem into account in the various studies being performed within the framework of the PREFACE and FANSTIC programmes.

In circumstances where a pilot is forced to follow a specified flight path, such as during a landing approach or in nap-of-the-earth conditions, it will be shown that there is an apparent modification of the helicopter's stability characteristics. This effect is identified in helicopter flight data from nap-of-the-earth agility trials where oscillations are observed in the time histories of the pilot's control inputs and the vehicle's response. A technique of predicting the nature of these oscillations using a linearised helicopter mathematical model is developed. The model is inverted to give the response of the unconstrained states in terms of those strongly controlled by the need to remain on a specific flight path. Results are compared with data from flight trials and it is shown that good correlation between the period of the oscillations in the flight data and the predicted values can be obtained.

Flows around two-dimensional rectangular cavities driven by thick shear layers are investigated experimentally at two supersonic Mach numbers (Me = 1.5 and 2.5) to show the effects of variations in Mach number and length to depth ratio of the cavity. Flow oscillation is observed in the cavity. The characteristics of the oscillatory behaviour are determined by Mach number and the length of depth ratio of the cavity, as well as the shear layer spanning the cavity. Two oscillatory mechanisms can be identified: one in which a strong trailing-edge vortex and vortices which are shed from the leading-edge interact, the other in which a transverse oscillation of a single vortex occurs within the cavity. Changes in the time-dependent and the time-mean flow characteristics at different flow conditions are discussed.

The time-dependent experimental results are compared with existing theoretical analyses of the frequencies. For one of these characteristic types of oscillation, the longitudinal oscillation, an existing theoretical description is improved with a modified phase relation.