Critical flight data (course, speed, threats, etc.) is displayed for the flight crew on their helmet visors. This look-through display is known as TVD (Through-Visor Display). The TVD is extremely useful as it means the crew does not have to lower its gaze from the combat environment when they need this information.
Unlike a standard HUD (heads-Up Display) which is projected only on the forward canopy, the TVD can be seen no matter where the Aerospace crew looks, and the information displayed in the TVD is updated based on the orientation of the crew member's head. In other words, it will show the craft's heading straight ahead when the pilot looks forward, but to his right when he looks left. This feature is extremely helpful when searching for targets that may not lie directly in the craft's flight path.
Another unique feature of the TVD is its ability to look 'through' the craft. This is accomplished by linking into the craft's sensors to produce a holographic image of what is under the craft. When the pilot puts the TVD on virtual mode, he can then look down and instead of seeing this instruments or the cockpit floor, he can actually see what he is flying over, along with all his standard flight information. Virtual mode is engaged with a switch which the crew member must keep depressed for the duration of their 'look-through'. Once the switch is released, normal vision returns. This prevents the pilot from looking down at a moment when he really does need to see his instruments and not being able to.
The TVD has several different modes for each crew member, and the particular mode needed can be selected from the stick controls. The computer narrows the options available based on the environment the aircraft is in to reduce erroneous selections. For instance, space flight modes are not available in atmosphere, landing mode is not available when there is no hard surface within 5,000 meters of the craft, etc.