SPECIFICATION OF THE INVENTION

1. Title of the invention

A novel system and method for in-flight correction of Aircraft Altitude to effectively carry out Aircraft Mission Requirements

2. Field of Invention

This invention relates to Aircraft Navigation and in particular to a method for correcting the inherent inaccuracies in measurement of an on-board altitude sensor.

3. Prior art and Draw backs of prior art

Aircrafts use various sensors among which the Barometric Altitude Sensor measures the aircraft altitude from the Mean Sea Level based on the local atmospheric pressure. The Atmospheric Pressure at any particular location on the earth surface is a dynamic parameter and is subject to change on a day-to-day basis. As a result, there are inherent inaccuracies in the measurement of the altitude by a Barometric Altitude Sensor.

4. Aim of the Invention

The main objective of the invention is to provide a novel method for correcting the altitude measured by a Barometric Altitude Sensor.

5. Summary of the present invention

This invention presents a method for in-flight correction of the Barometric Altitude of the aircraft for accurately carrying out Aircraft missions. It uses the elevation of a known ground based Waypoint (WP), the measured Barometric Altitude and the Pilot Inputs on the Hand Controller for applying corrections to the measured aircraft altitude.

As shown in Figure 1, the Aircraft height above the Waypoint is calculated by the Computed Height Module, 101 by taking the difference between the Barometric Altitude received from Air Data Module, 105 and the Waypoint Altitude received from WP Database Module, 102. Based on this initial calculated altitude, the symbol for the WP is overlaid by the Display Module, 104 in the pilot's field of view on a Head Up Display (HUD), 107. If the symbol does not coincide with the WP in the field of view, the pilot can use the dedicated keys (H+ & H- keys) on the Hand Controller, 103 to apply correction to the altitude of the aircraft over the WP. This change in altitude gets translated to a change in the symbol position on the HUD, and by repeating this process the symbol is made to coincide with the ground based WP. The final correction obtained above is used to correct the Barometric Altitude measurement.

6. Brief Description of the Drawings and Tables

Figure 1 is a block diagram of the System for correcting the Barometric Altitude of the aircraft.

Figure 2 depicts the various altitude parameters involved in correcting the Barometric Altitudeof the aircraft.

Figure 3 depicts the scenario w.r.t the HUD and Pilot's view.

Figure 4 depicts the flowchart for correction of Barometric Altitude.

Table 1 lists the correction values applied to Aircraft Height above WP on pressing dedicated hand controller button.

7. Detailed Description of the Invention

For carrying out Aircraft missions, it is necessary to accurately calculate the aircraft altitude w.r.t. the ground/terrain. The aircraft altitude determined using the Barometric Altitude measurement from the on-board Air Data Module, 105 is prone to errors as it is dependent on the Atmospheric Pressure, which varies with time and location. This invention provides the pilot with the option for correcting the aircraft altitude calculated from the Barometric Altitude using a known Way Point elevation form mean sea level and cues displayed on the Head up Display of the Aircraft.

It consists of Computed Height Module (101), WP Database Module (102), the Hand Controller (103), Display Module (104), Air Data Module (105) and Inertial Navigation Module (106), and the Head Up Display (107) as shown in Figure 1.

As shown in Figure 2, the Aircraft height above a known WP is calculated by taking the difference of the Barometric Altitude and the known WP elevation. The horizontal range is calculated from the present aircraft position and WP position received from Inertial Navigation Module, 106 and WP Database Module, 102 respectively. The calculated altitude and horizontal range w.r.t. the WP is used to overlay symbols corresponding to the WP in the pilot's field of view on the Head Up Display, 107. This scenario is shown in Figure 3.

When the measured Barometric altitude has errors, the WP symbol overlaid on the HUD will not coincide with the actual WP on the field of view. As depicted in Figure 3, for the incorrect Barometric altitude measured, the height above the WP is given by the quantity 3F, and the corresponding symbol for this calculated altitude is 3C. When the pilot applies the correction to the Barometric altitude, the altitude above the WP changes to 3G and the WP symbol corresponding to that altitude is 3D. When the symbol at 3D coincides with the WP in the field of view, we get the actual height above the WP.

The height calculation is carried out by the Computed Height Module, 101. It takes the difference between the Barometric Altitude and WP elevation received from the Air Data Module, 105 and WP Database Module, 102 respectively, to get the initial height above the WP, (HcowOimtiai (shown in Figure 4 as Step 401). The Display Module, 104 receives the aircraft height above WP, and generates the WP Azimuth and Elevation Data for generation of display cues on the Head up Display, 107.

Based on the displayed WP symbol on HUD, the pilot presses the H+/H- input of the Hand Controller, 103, to apply correction to the computed height above the WP. Pressing the H+ button decreases the height of the aircraft above the WP (Step 406c) and pressing the H- button increases the height (Step 406d). The pilot continues to apply the correction till the displayed WP symbol on HUD coincides with the WP in his field of view. The amount of height compensation applied depends on the duration for which the pilot presses the H+/H- button, the details of which are given in Table 1.

It is to be noted that decreasing the aircraft altitude will translate to an upward movement of the WP symbol on the Head Up Display, and increasing the altitude makes it move downwards. Hence the press of H+ is used to decrease the altitude and H- is used to increase the altitude, to correspond to the WP symbol moving up and down respectively.
Table 1 Table of values for Correction of Aircraft Height above WP symbol moving up and down respectively.

The following relations are used for correcting the aircraft height above the WP:

If "H-"JS pressed, then
HCOM = HCOM +AHT (1)

If "H+" is pressed, then

HCOM = HCOM -AHT, (2)

where HCOM is Computed Height of aircraft above the WP and initial value of HCOM is given by

(HcoM)initial Barometric Altitude - Stored WP Altitude (3)

The frequency of updating the altitude depends on the length of the key press. For a press of duration lesser than 1 sec, the height update is applied every 200 ms (AT in Steps 405, 406), else the height is updated every 100ms (AT in Steps 408, 410, 406). The upper limit for the height compensation applied is fixed at ±2000 ft.

The Display Module, 104 receives the updated aircraft height above WP, (HcoM)corrected and display cues on the Head up Display, 107, which will coincide with the WP.

CLAIMS

We claim

1. A novel system employing a methodology for on-board correction of Barometric Altitude using position and altitude of a known Waypoint and pilot inputs from the hand controller.

2. The system of claim 1, which comprises of Air Data Sensor Module, Inertial Navigation Module, Waypoint Database Module, Computed Height Module, Display Module, a Head Up Display and a Hand Controller.

3. The method of claim 1, as implemented in the Computed Height Module, which is characterized by aircraft altitude computation using barometric altitude, the position and altitude of a stored waypoint and pilot input from the hand controller.