Screen/head stabilized MIL-STD 1295 Helmet Mounted Display (HMD) flight symbology as integrated on the Apache helicopter was compared to world referenced/stabilized flight symbology. Simulation test results indicate that pilots perform significantly better using world stabilized conformal attitude symbology. They were accurate to an average of 1/2 degree at estimating terrain relief and aerial target locations. Pilots were able to take advantage of world referenced symbology due to the unique features of HMD that allow the pilot to visually use the symbology at extreme azimuth and elevation off-axis angles. World stabilized conformal symbology was also preferred while performing contour flight tasks. They reported that the use of climb-dive-marker during contour flight greatly reduced pilot work load under conditions tested. Cyclic input errors occurred when using both MIL-STD 1295 hover symbology and test symbology indicating that a better approach for depicting hover symbology is warranted. The magnitude of cyclic input and spatial estimation errors increased as the off-axis viewing angle became larger.