The foresight of Arthur C. Clark in suggesting that television pictures by way of a satellite could be sent direct to the viewer's home is about to come true. Whilst the professional communications fraternity have been using satellites for years for point to point communications it is only with the coming of high power satellites will viewers be able to receive pictures without the intervention of a terrestrial common carrier.

The microprocessor revolution can in no way be described as a ‘silent’ revolution, unusually perhaps, a technological advance has caught the imagination of the mass media, who are fond of postulating its effect on our lives.

Within the Air Transport industry much coverage has been given to the development of ‘visibly’ different avionic equipment such as cathode ray tube (CRT) flight instrumentation, active control technology and flight management systems. These advances have been made possible solely on account of the microprocessor, which has, in addition, also revolutionised existing avionic disciplines.

Airworthiness is not clearly enough defined for its management to be a teaching objective in itself. It is in any case not the principal aim of the aircraft operator but subsidiary to the transport function. Education in the management of air transport engineering is directed towards the process of producing aircraft fit to be used for their economic purpose and the management of airworthiness is inextricably embedded in it.

Nevertheless a number of subject areas which such courses should include can be identified as relevant to current airworthiness problems.

The rapid frequency sweep technique is the result of a considerable amount of research into the development of a transient method for the rapid measurement of structural frequency response, digital data analysis procedures being used to derive the required dynamic characteristics. Theoretical analyses, together with the results of experimental studies and experience gained during structural testing are presented here which illustrate practical considerations and limitations of the method; these range from discussion of exciter attachment, effects of transducers and choice of instrumentation to signal processing methods and related criteria. A simple guide to practical structural testing is given in the final section which outlines procedures to be followed during testing and signal acquisition.

The large number of enquiries received by the BHAB show that there is a need for basic guidelines on this subject. These are given here but more detailed information is available from the Civil Aviation Authority, AS4.

Any owner of a piece of ground may use it as a helicopter landing facility without any kind of permission, provided the following conditions are met:

1. a. It is not in a congested area, as defined in Article 90 of the Air Navigation Order 1976, that is, any area which is substantially used for residential, industrial, commercial or recreational purposes.

   (Note: In this context, the CAA considers the term “substantial’ to mean 50% or more.)

2. b. No structure is erected in connection with its use as a helicopter landing area, eg concrete landing pad, hangar,etc, other than a temporary structure such as a windsock.

3. c. Its usage is confined to the private or business use of the owner, his employees or anyone specifically visiting him for social or business purposes.

4. d. A pilot using the site will be able to conform with Rule 5 of the Rules of the Air and Air Traffic Control Regulations 1976.

The first geostationary satellites were subject to a number of constraints stemming both from the relatively modest performance of the technique available at the time and from the payload capacity of the launchers used. Such constraints were either technological, eg, the modest power levels of the onboard transmitters or the highest usable frequency, or else economic, particularly the cost of placing a kilogram of satellite in geostationary orbit. At the time, these factors entailed the use of high-performance costly ground stations, which could be operated economically only for long-distance (intercontinental) communications between major traffic centres.

Morgan and Saunders have shown that highly peaked velocity profiles can be produced in a pipe downstream of a partial gauze screen, a screen pierced by a central hole. By systematically varying the ratio of hole size, d, to pipe diameter, D they obtained peaked profiles with different values of profile peakiness û/ū.

The investigation showed that two different velocity profiles with the same value of û/ū. could be produced from a particular gauze, one from a screen with d/D <0·5 and the other with d/D>0·5.