A Modern Flight Instrument System

Abstract

ALMOST all the long-range civil transport aircraft entering service during the next few years will be equipped with some form of instrument system. It is proposed to describe here some aspects of the* developments which have been embodied in one such system, the Smiths Flight System, and to indicate its scope when applied to the operation of such aircraft.Since the war the operation of a high-performance transport aircraft on congested and competitive routes has become an increasingly complicated process. With the advent of the gas turbine, cruising speeds have doubled, and at the same time there has been a tendency towards higher standards of economy and safety. The development of the air traffic control system has brought about a demand for greater precision in navigation, and in the most congested areas by far the greatest number of flights are conducted under instrument conditions. Meanwhile, aircraft have also become more complex, and the pilots themselves are often expected to monitor the operation of the controls and instrumentation associated with the engines, electrics and pressurization as well as carry out the navigation. This extra work has had to be undertaken without any relaxation of the general vigilance which constitutes good airmanship.Improvements in the accuracy and reliability of the basic flight instruments, and the development of new types of instrument have helped the pilot. Apart from the provision of the basic information on heading, attitude and that derived from the basic quantities of pitot and static pressure, it has now become necessary to display the output of the various radio aids. The Radio Magnetic Indicator has provided an effective display of the relative bearing of two m.f. radio beacons viewed against the reference of a rotating compass card. With its extension to display the relative bearing of a VOR transmitter it is still without equal as a combined display of both absolute and relative bearing.Track guidance has become the foundation of many of the radio systems and is convenient from an air traffic control point of view. The Instrument Landing System is a three dimensional example of such a facility. From the earlier presentation of track deviation on the familiar deviation indicator, a number of flight director instruments have been developed. These are all based on the 'quickening' of the pilot's response to a track deviation signal by computing it with the other parameters: the track to be flown, the aircraft's heading, and its bank angle. The result is then displayed on a suitable indicator, which has eased the pilot's load by 410

Heading Definition in Commercial Aircraft

“…Despite the remote mounting of the detector unit some deviation errors remain, and aircraft compasses are usually designed so that the classical A, B and C corrections (datum misalignment and hard iron effects) can be made. 1 During a compass swing there is always a great deal of difficulty in representing the aeroplane in its operational form. Disturbances to the local magnetic field can be caused by iron in the runway, the position of the undercarriage, the attitude of the aeroplane and the operation of its engines and domestic power supplies.…”

The Perfection of the Gyro-Magnetic Compass

“…This systems concept produced the modern integrated instrument and flight control systems and a number of these have since been developed. 4 Most of them included a gyro-magnetic compass as an integral part. In 1959-60, when considering the requirements for a military version of a second generation flight control system for transport aircraft, 6 it was decided that, while the most accurate forms of heading reference such as an inertial system or a star tracker would not be feasible because of cost and complexity, the accuracy of gyro-magnetic compasses then available was not quite adequate.…”