EMI problems & its countermeasures during the testing of Head-Up-Display for trainer aircraft

In today´s modern supersonic aircrafts, a split of seconds decision is required from pilot in coping with the continual eye adjustments for focus, brightness of symbology displayed, the line of sight between various displays of cockpit and the outside world. Many avionics display systems have been designed throughout the world. Head-Up-Display (HUD) is one of the important and critical systems in the cockpit of an aircraft. In fighter aircrafts, it is placed just in front of the pilot´s eyes. Critical flight information is presented to the pilot superimposed on his outside field of view. An ingeniously designed and developed Head-Up-Display for Trainer aircraft by CSIO was subjected to EMI-EMC tests -CS01, CS02 & CS06 & RE02. The system´s behavior w.r.t. EMI specifications (as per MIL STD 461C) and measures adopted are reported briefly in this paper. HUD can operate in three modes (i) Stroke/Cursive Mode (ii) Stand-By-Sight Mode (iii) Mixed (Cursive in Raster) Mode. The performance and behavior of HUD symbology in first two modes was continuously monitored from design eye position. During CS01 test, it was found that symbology displayed on HUD was shaky in Stroke mode while it was stable in the Stand-By-Sight Mode. In RE02 test, unit was not in compliance with MIL STD requirements with emission levels exceeding the limit line. In this paper, authors have highlighted the problems faced & remedies adopted during the tests to achieve EMC against emission levels.