Grace's Guide is the leading source of historical information on industry and manufacturing in Britain. This web publication contains 147,939 pages of information and 233,602 images on early companies, their products and the people who designed and built them.
~ NB this is part of Plessey Co
1974. of Ilford, Essex. Managing director— F. K. Chorley; sales manager avionics— M. I. Dodd. Airborne UHF/VHF transmitter/receivers—PTR175, PTR377, PTR1721 and PTR170 (UHF only); airborne integrated data acquisition and recording systems including advanced large-capacity PV740 system for the Boeing 747, PV1573 system for ARINC 573 for Concorde and wide-bodied aircraft and comprehensive flight-test systems; aircraft weapon control and stores management systems; missile guidance systems; radar altimeters; target aircraft telecommand systems. 
1989 Plessey Avionics announced a computer-based inflight entertainment and telephone system which it was offering to major airlines with no capital expenses by the airlines and profits shared; the idea has originated with a company called Candlestar and had evolved from military hardware
Later see GEC-Plessey Avionics