Head Worn Display for use in Unusual Attitude Recovery
Publication Date: 2014-Apr-14
The IP.com Prior Art Database
Loss of Control is a primary concern in aviation. Erosion of piloting and monitoring skills, due to over-reliance on automation, can lead to delayed or incorrect recovery from an Unusual Attitude. A Head Worn Display (HWD) can provide the pilot with a means to view the location of the natural horizon, and other references, continuously without the constraints associated with fixed flight deck displays. The ability for the pilot to reference the horizon, along with specific HWD symbology, affords an efficient and rapid recovery to normal flight following an Unusual Attitude excursion.
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Commercial Aviation has an excellent safety record. High standards for pilot training, coupled with the reliability and safety of today's commercial aircraft, has led to an extremely low probability rate for accidents and incidents. However, it has been observed that over-reliance on automation and lack of flight crew experience is leading to an erosion of piloting and flight monitoring skills. This is most evident when aircraft depart from a low energy state and enter a stall, or are upset due to turbulence.
Recovery maneuvers from a low energy state or unusual attitude have to be initiated by the pilot, and rely on instrument interpretation to manually maneuver the aircraft back to a stable state. Because of the fixed location of flight deck displays, today's Primary Flight Displays (PFDs) are limited in their ability to render the horizon line once the aircraft has exceeded a certain pitch angle. Figures 1 and 2 show the aircraft in an unusual pitch attitude:
Figure 1 Unusual Attitude - Pitch Up
Figure 2 Unusual Attitude - Pitch Down
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Chevrons are used to direct the pilot to the horizon line, which is where the aircraft ultimately needs to be returned to for stable flight. By regulation, a portion of the ground or sky (depending on whether the aircraft is pitched up or down) has to be visible on the display. At very high or very low pitch angles the horizon line (zero degree pitch line) disappears from the display. To provide a portion of ground or sky, the horizon line becomes "parked" at the top or bottom of the display, as shown in Figures 1 and 2.
This dashed "virtual" horizon line only indicates the direction of the real horizon. The degree to which the aircraft has to be pitched up or down to return to the natural horizon has to be interpreted by the pilot based on the indicated pitch angle. As can be seen in Figure 2, even though the horizon line appears to be about eight degrees above the aircraft, the aircraft is actually at minus twenty degrees of pitch and will have to traverse that angle to return to straight and level.
With the addition of an excessive roll angle (as shown in Figure 3), the ability to deduce the actual aircraft attitude depends entirely on the pilot's ability to correctly interpret the display.
Figure 3 Unusual Attitude - Roll Right
The Head Up Display (HUD) is impacted by the same issue, only the horizon line will tend to become non-conformal at a smaller pitch angle. Given that the HUD pitch tape is normally conformal to the outside scene, and that the HUD's vertical Field of View is limited to 30 degrees (typically about 10 degrees up and 20 degrees down from the boresight) the aircraft may only need to pitch down 8 degrees or so before the horizon line becomes non-conformal (see Figure 4).
Figure 4 Head Up Display - Normal Format
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At this point, the HUD behavior deviates from that of the PFD in that the pitch scale now compresses to keep the hor...