MODUK - AVP 118
Guide to Electromagnetic Compatibility in Aircraft Systems (12.76)
|Publication Date:||1 January 1976|
AvP 118 has been written to help aircraft constructors and those concerned with the design, development and installation of equipment and systems in aircraft. Its object is to ensure that when such equipment or systems are installed in the complex electromagnetic environment of an aircraft, they will operate satisfactorily and will not cause unacceptable degradation of performance or malfunction of other equipment required to operate simultaneously.
Design manuals have been prepared, notably by the three US Services, which cover the subject of EMC in considerable detail, and include extensive theoretical data. AvP 118 does not attempt to cover the subject to the same depth, and it does not include theoretical data. A practical approach is taken, and Appendix B includes new information on the actual electromagnetic environment gained from a programme of surveys on a large number of different types of aircraft carried out by the Electrical Research Association during the period 1971 to 1974 under a contract placed by the Ministry of Defence. The surveys included measurements of both conducted and radiated electromagnetic emissions from the many sources on board, of the electric and magnetic field strengths within the fuselage, the r.f. impedance of d.c. power cables, coupling between cables and the attenuation provided by the fuselage. Many of the measurements were made both on the ground and in flight.
AvP 118 gives advice on many aspects of EMC. It discusses all types of interference, over a frequency range from 20 Hz to 40 GHz, including that generated within the aircraft itself, from the aircraft's own transmitters, from external transmitters and from external sources such as electrostatic charging and lightning.
The nature of the interference encountered and the mechanism of its generation and propagation are discussed, together with methods of control. Methods of measuring interference, both in the laboratory and in the aircraft, are given. Advice is included on installation, and recommendations are made which should help to achieve EMC.
Emissions concerned with 'secure information' and electronic countermeasures (ECM) are not discussed because of their classified nature. The effects of electromagnetic pulses (EMP) associated with a nuclear explosion are dealt with in other specialized documents, some of which are referred to in Appendix C. However, the techniques used to achieve satisfactory EMC and the shielding effect of the aircraft's skin may also be beneficial to all three types of installations.
Frequency assignment or allocation is not dealt with, nor are the techniques used to overcome frequency overlapping such as blanking and time-sharing. The fundamental design of receivers and transmitters is not discussed.
AvP 118 has been written solely as a guide. Its recommendations are advisory, not mandatory. Mandatory requirements are given in AvP 970 'Design requirements for Service aircraft'.