WHEN AUTOMATED GUIDANCE SYSTEM IS IN USE

BACKGROUND OF THE INVENTION

1. Field of the Invention This invention relates generally to ground proximity warning systems, and more particularly to a ground proximity warning system usable with automated guidance systems such as flight directors, flight management systems, auto pilots and flight guidance systems for the purpose of warning the pilot when the automated guidance system is guiding the aircraft along an unsafe flight path.

2. Description of the Prior Art

Various ground proximity warning systems that warn the pilot of an aircraft of an unsafe flight condi¬ tion are known. These systems generally monitor various flight parameters, such as radio altitude and rate, barometric altitude and rate and deviation from the glideslope and generate warnings in the event of in- sufficient terrain clearance, excessive closure rate, excessive barometric sink rate and deviation below the glideslope beam.

Various automated guidance systems such as flight directors, flight management systems, auto pilots and flight guidance systems are also known. These devices employ gyros to provide heading and pitch infor¬ mation and an artificial horizon. In addition, these devices receive glideslope and localizer beams that they

couple onto in order to guide the aircraft to the touch¬ down point on the runway.

While both devices have substantially increased airline safety, occasionally an automated guidance system may not couple onto the glideslope or localizer beam and guide the aircraft along an unsafe flight path. In such a situation, it is desirable to advise the pilot of such a condition.

There have been instances where aircraft have been flown into terrain by an automated guidance system without the pilot realizing that something was wrong. In some cases, the ground proximity warning system aboard the aircraft even gave a warning before impact, but the warning was disregarded by the pilot because he believed that the automated guidance system was operat¬ ing properly and that the warning given was a nuisance warning.

SUMMARY Accordingly, it is an object of the present invention to enhance the warning capabilities of ground proximity warning systems.

It is another object of the present invention to provide a ground proximity warning system that co¬ operates with an automated guidance system to monitor the flight path when an automated guidance system is in use and to advise the pilot of an unsafe flight path.

It is another object of the present invention to provide a ground proximity warning system that deter¬ mines whether an automated guidance system is being used, and if so, to monitor the altitude of the aircraft above ground and to warn the pilot if the aircraft drops below a predetermined minimum altitude while being guided by the automated guidance system.

It is another object of the invention to pro- vide a system that monitors the localizer beam and advises the pilot of an excessive deviation from the

localizer beam while the aircraft is being guided by the automated guidance system.

BRIEF DESCRIPTION OF THE DRAWING These and other objects and advantages of the present invention will become readily apparent upon con¬ sideration of the following detailed description and attached drawing, wherein:

The single figure is a block diagram of the warning system according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing, the system according to the invention is generally designated by the reference numeral 10 and contains a ground proximity warning system 12 that may be a relatively sophisticated ground proximity warning system such as the Mark VII ground proximity warning system manufactured by Sundstrand Data Control, Inc. of Redmond, Washington, or a system as disclosed in, for example. United States Patent No. 3,946,358, incorporated herein by reference. When a multiple mode ground proximity warning system is used as the ground proximity warning system 12, it receives a radio altitude and a radio altitude rate signal from a radio altitude source 14, a baro¬ metric altitude and rate signal from a barometric source 16 and a glideslope deviation signal from a glideslope receiver 18. Alternatively, a Z-velocity signal from an inertial navigation system may be used instead of the barometric altitude rate to provide vertical velocity information. In addition, the ground proximity warning system 12 receives a signal from an automated guidance system such as a flight director or a flight guidance system or other similar device 20. The ground proximity warning system 12 receives signals representative of the status of the flight director or flight guidance system. The status signals may take the form of arming logic

outputs that are normally used for flight deck annuncia¬ tion of status during the approach process. These signals indicate whether the flight director or flight guidance system is armed, and also indicates the par- ticular modes of operation of the flight director or flight guidance system 20 that have been armed. In addition, the ground proximity warning system 12 receives signals from a localizer receiver 22 that pro¬ vides an indication of the deviation of the aircraft from the localizer beam. An annunciator 24 receives advisory and warning messages generated by the ground proximity warning system 12 and relays them to the pilot. The annunciator 24 may be either a visual or an aural annunciator, but an aural annunciator is prefer- able because it is able to provide specific voice messages generated by the ground proximity warning system 12 to the pilot in order to provide him with specific information defining the problem.

A modern automated guidance system such as the flight director or flight guidance system 20 has many modes of operations, among them a glide path mode, a localizer mode and an altitude mode. When the glide path mode is armed, the flight director or flight guid¬ ance system 20 captures the glideslope beam and guides the aircraft along the glideslope beam at approximately a 3' angle toward the end of the runway. When the localizer mode is armed, the flight director or flight guidance system 20 acquires the localizer beam that pro¬ vides azimuth information and guides the aircraft along a path in line with the runway center line. In the altitude mode when the altitude mode is armed, a pre¬ determined altitude is selected and the flight director or flight guidance system maintains the aircraft at the preselected altitude. The status signals from the flight director or flight guidance system 20 are received by the ground proximity warning system 12 and compared with signals

from the radio altitude signal source 14 to determine whether there is sufficient terrain clearance when the flight director or flight guidance system 20 is being used by the pilot. For example, when the glide path mode is armed, but the flight director or flight guid¬ ance system has not coupled or captured the beam, i.e., is not on track with the beam, and the aircraft is at less than a predetermined altitude, for example, 1000 feet above the ground, something is wrong. In such an event, an appropriate advisory message could be given to the pilot. Examples of such messages are "TOO LOW, TERRAIN", "GLIDESLOPE", "GLIDESLOPE NOT COUPLED", and a readout of the altitude, for example 1000 feet could also be given. Similarly, if the localizer mode of the flight director or flight guidance system is armed but the flight director or flight data system has not coupled to the localizer beam, and the aircraft is at less than a predetermined minimum altitude, for example, 1000 feet, another condition specific advisory message would be given. An example of such a message is "TOO LOW, TERRAIN", "LOCALIZER, LOCALIZER NOT COUPLED". An announcement of the altitude could also be made. In addition, the deviation signal from the localizer 22 can also be monitored. If the flight director or flight guidance system 20 is engaged and if the localizer devi¬ ation becomes more than one dot above the runway, some¬ thing is also wrong and an appropriate such as the message above could also be given. If the altitude mode is armed and the altitude has not captured, and with the aircraft is below a pre¬ determined altitude above ground, for example, 500 feet above ground level, there is also something wrong. In such an event, an appropriate message such as "TOO LOW, TERRAIN" can be generated to apprise the pilot of a specific dangerous condition being encountered.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. Thus, it is to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described above.

What is claimed and desired to be secured by Letters Patent of the United States is: