Communications: electrical – Aircraft alarm or indicating systems – Flight alarm
Reexamination Certificate
2000-02-01
2002-04-30
Swarthout, Brent A. (Department: 2632)
Communications: electrical
Aircraft alarm or indicating systems
Flight alarm
C340S961000, C340S963000, C340S969000, C342S065000, C701S004000, C701S009000, C701S301000
Reexamination Certificate
active
06380870
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to ground proximity warning systems for use in aircraft. More particularly, the apparatus, methods, and computer program products of the present invention relate to determining a look ahead distance value for use in a ground proximity warning system that provides a desired reaction time for high speed flight.
BACKGROUND OF THE INVENTION
An important advancement in aircraft flight safety has been the development of ground proximity warning systems. These warning systems analyze the flight parameters of the aircraft and the terrain surrounding the aircraft. Based on this analysis, these warning systems provide alerts to the flight crew concerning possible inadvertent collisions of the aircraft with surrounding terrain or other obstacles.
Although these warning systems are quite useful in providing the flight crew with information concerning potential problems with the navigation of the aircraft, the usefulness of these systems must be balanced against problems associated with the generation of nuisance alarms. Specifically, although it is advantageous to provide the flight crew with as much information as possible concerning terrain and obstacles in the flight path of the aircraft, this information should be delivered to the flight crew in a timely manner, such that the flight crew will pay close attention to these alarms. If alarms are provided too far in advance to the flight crew concerning terrain that is still far away from the present position of the aircraft, the flight crew may become desensitized to the alarms and may potentially ignore alarms from the ground proximity warning system altogether. Further, the generation of alarms concerning terrain that is still far away from the present position of the aircraft may also add stress and confusion on the flight crew and may overshadow other more critical alarms in the cockpit.
For this reason, at least one ground proximity warning system includes techniques that limit the number of potential nuisance alarms generated. This ground proximity warning system uses a look ahead distance value that defines a distance surrounding the aircraft in which the ground proximity warning system will provide alarms to the flight crew concerning potential ground proximity danger. This look ahead distance is further divided into advisory and warning regions, such that advisory alarms are generated for potential problems with terrain located at the outer extremities of the look ahead distance, while warning alarms are provided for problems with terrain located nearer the current position of the aircraft.
The look ahead distance value used by this ground proximity warning system is typically based on the flight parameters and flight characteristics of the aircraft. For example, the look ahead distance value may be based on the ground speed of the aircraft, actual roll angle of the aircraft, and/or a characteristic turning radius associated with the type of aircraft. The look ahead distance value may also be based on the proximity of the aircraft to a selected runway. Specifically, as an aircraft approaches a runway for landing, the look ahead distance value is typically decreased to reduce the number of nuisance alarms and focus on potential problems within the immediate surroundings of the aircraft.
In addition, the look ahead distance value is typically limited to minimum and maximum values. A minimum look ahead distance value is typically chosen to provide a minimum reaction time, while a maximum look ahead distance value is typically chosen to reduce the number of nuisance alarms generated.
As an example, one of the look ahead distance values typically used by the ground proximity warning system is based on the speed of the aircraft and a characteristic turning radius associated with the aircraft. This look ahead distance value is referred to as the ground speed look ahead distance value and typically provides a look ahead distance value based on the speed of the aircraft and the reaction time required for the aircraft to perform two turning radii plus an added reaction time. The equation for the determination of this ground speed look ahead distance is:
LAD
Ground Speed
=0.00278(Vg)+0.000050568(Vg
2
)+K
where
LAD=ground speed look ahead distance in nm,
Vg=ground speed in kts, and
K=constant.
The derivation of this equation is discussed in detail in U.S. Pat. No. 5,839,080 to Muller, entitled “Terrain Awareness System” which is assigned to the assignee of the present application. The derivation of this equation is also provided later below.
FIG. 1
depicts this equation graphically in terms of look ahead distance versus ground speed. As can be seen, for aircraft speeds in the range of 100 kts to 250 kts, the look ahead distance value varies with ground speed. For aircraft speeds below 100 kts, the ground proximity warning system limits the look ahead distance value to 0.75 nm. This lower limit is used to ensure that a proper minimum look ahead distance is maintained. The ground proximity warning system also limits the look ahead distance by an upper limit of 4 nm for speeds exceeding 250 kts. The upper limit of the look ahead distance value is provided to reduce the number of nuisance alarms generated.
Although limiting the distance surrounding the aircraft in which ground proximity warning alarms are generated is advantageous as it reduces nuisance alarms, there may be some drawbacks. Specifically, if the aircraft is traveling at a high rate of speed, of for example in excess of 250 knots, the limited look ahead distance may not provide desired reaction times for the aircraft to perform an evasive maneuver. For example,
FIG. 2
illustrates a plot
2
of the reaction time as a function of aircraft speed and look ahead distance. Specifically, the plot depicts the reaction time provided by the look ahead distance for the given speed of the aircraft, i.e., Reaction Time=LAD/Speed.
As illustrated in
FIG. 2
, for aircraft speeds in the range of 100 kts to 250 kts, the reaction time increases, however, above 250 kts, where the look ahead distance is limited to 4 nm, the reaction time begins to decrease, shown by decreasing portion
4
of plot
2
. For example, at 250 kts, the look ahead distance value provides a reaction time of approximately 55.5 seconds. However, at 360 kts, the reaction time has been reduced to 40 seconds. Thus, while the above approach provides a mechanism for reducing the number of nuisance alarms provided to the flight crew, with increased aircraft speeds, the reaction time may be reduced to a point where it is more desirable to provide at least some minimum reaction time.
One solution to the problem of reduced reaction time for increased aircraft speeds could be to increase the maximum limit of the look ahead distance value to a value greater than the current 4 nm maximum limit. This would allow for increased look ahead distance values at higher aircraft speeds. However, as illustrated in the above equation, the look ahead distance value is a function of the square of the speed of the aircraft. Thus, for small increases in aircraft speed, the look ahead distance value will increase significantly. As such, increasing the maximum look ahead distance limit above the current 4 nm maximum limit may undesirably increase the number of nuisance alarms.
In light of this, it would be desirable to have a ground proximity warning system that generates a look ahead distance that provides a desired minimum reaction time when the aircraft is traveling at higher speeds, while at the same time reducing the number of nuisance alarms generated.
SUMMARY OF THE INVENTION
As set forth below, the apparatus, methods, and computer program products of the present invention overcome many of the deficiencies identified with using a limited look ahead distance value for high speed flight. The present invention provides several apparatus, methods, and computer program products for determining a look ahead distance value for use in a ground pr
Conner Kevin J
Johnson Steven C.
Honeywell International , Inc.
Swarthout Brent A.
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