Abstract: In modern warfare scenarios military helicopters have to be able to operate in NoE envelopes under all meteorological conditions. Under daytime good weather conditions this poses no problem for well-trained aircrews. In nighttime or bad weather conditions however the use of electronic sensors like IIT or TI is necessary. The aircrew use these devices for obstacle detection and avoidance and flight attitude perception. Flight below tree top level is only feasible when both of these tasks can be accomplished safely throughout the whole flight. For this reason the pilots must fly visual at all times. Relying on instruments for flight attitude control when flying between the trees would surely result in the striking of obstacles. These facts and the necessity for the aircrew to view greater azimuth angles than fixed wing pilots imply differing equipment and symbology packages for the two aircraft species. As a matter of fact only helmet mounted displays are really useful for helicopter flight control symbology. The following are results of experience from a number of trials with symbology in helicopters in low level flight down to 10 feet at night with IITs. !0
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