CA1243117A

CA1243117A - Altitude loss after take-off warning system utilizing time and altitude

Info

Publication number: CA1243117A
Application number: CA000498123A
Authority: CA
Inventors: Michael M. Grove
Original assignee: Sundstrand Data Control Inc
Current assignee: Sundstrand Data Control Inc
Priority date: 1985-02-22
Filing date: 1985-12-19
Publication date: 1988-10-11
Also published as: FI864240A; US5283574A; EP0214272B1; EP0214272A4; WO1986005022A1; EP0214272A1; DE3687331D1; JPS62500200A; AU5624786A; FI864240A0; DE3687331T2

Abstract

ALTITUDE LOSS AFTER TAKE-OFF WARNING
SYSTEM UTILIZING TIME AND ALTITUDE
Abstract of the Disclosure Warning systems for aircraft that provide a warning to the pilot of an excessive altitude loss or an excessive descent rate after take-off as long as he is flying below a predetermined altitude save the problem that they require a valid radio altitude signal for proper operation, and tend to generate nuisance warnings when used in low flying aircraft. This problem is solved by comparing the accumulated altitude loss after take-off (12, 14, 62, 34) with the product of a barometrically derived altitude and the length of time the aircraft has been flying (12, 14, 30, 32, 34). A warning is generated if the altitude loss is excessive for the accumulated time-altitude product after take-off (38, 40). Thus, the system is more sen-sitive immediately after take-off and becomes less sensitive as flight time is accumulated to permit low level maneuvering without generating false or nuisance warnings, and does not require a valid radio altitude signal to generate a warning.

Description

12~311~7 ALTITUDE LOSS AFTER TAKE-OFF WARNING

S ~
This invention relates generally to the field of ground proximity warning systems, particularly to ~ystems that warn of an excessive aircraft altitude loss after take-off or doing a go-around after a missed approach, and even more particularly, to systems where-in ~he warning criteria are altered as a function of elapsed time after ta~e-off as well as the altitude above ground at which the aircraft is flying.
Descr_e~ion of th~ i9~
Ground proximity warning systems that warn of aircraft descent after take-off or during a go-around after a missed approach are ~nown. Examples of such systems are disclosed in United States Patent Nos. 3,946,35~; 3,947,80~; 3,Y47,810; 4,319,218 and 4,433,323 assigned to the assignee of the present invention. The sy~tems disclosed in the '358 and '808 patents provide a warning if the descent rate of the aircraft exceeds a predetermined rate below a given altitude, and the systems disclosed in the '810; '218 and '323 patents generate a warning if the altitude loss exceeds a predetermined value before a predetermined altitude is reached. The '323 patent also discloses a system that switches ~etween modes based on time and radio altitude.

~2~31i7 While these systems provide a way to warn the pilot of an aircraft of a hazardous condition resulting from an excessive sin~ rate or from an excessive altitude loss after take-off or missed approach, tbese systems do not ta~e into account the length of time that the aircraft has been flying in determining the warning envelopes. Consequently, ~uch systems are not entirely suitable for aircraft whose operational characteristics are such that they are normally flown at low altitudes after ta~e-off, because such systems can generate nuisance warnings during intentional low level maneuvering. In addition, many aircraft have radio altimeters that provide unreliable readings immediately after ta~e-lS off, and systems that rely solely on a radio altimeter for altitude information are generally inhibited until the radio altitude readings stabilize.
~L~
Accordingly, it is an o~ject of the present invention to provide an excessive loss after take-off warning system that overcomes many of the disadvantages of the prior art systems.
It is another object of the present invention to provide an excessive altitude loss warning system particularly suitable for low flying aircraft.
It is another object of the present invention to provide an excessive altitude loss warning system that does not require a radio altitude signal to generate a warning.
It is yet another object of the present invention to provide an excessive altitude loss warn-ing system having a warning envelope that is a function of ~oth altitude and the length of time that the aircraft has ~een flying.

~2~311~

The operation and the flight characteristics of ~ost aircraft, such as transport aircraft, are ~uch that the aircraft tends to clim~ steadily after ta~e-off. Should such an aircraft lose an excessive amount of altitude or sink at an excessively high rate prior to reaching a predetermined altitude, a hazardous situation can occur. Consequently, ground proximity warning systems have been developed to warn the pilot of an excessive sin~ rate or altitude loss Rt low altitudes. Such systems are generally deacti-vated to prevent nuisance warnings above a predeter-mined altitude where an inadvertent descent will not cause a potentially hazardous flight condition.
Certain other aircraft, particularly carrier based aircraft ~uch as the Loc~heed S3-A often ta~e off, for example from the deck of a carrier, and con-tinue to fly at low altitudes ~ather than continulng to clim~ as does, for example, a transport aircraft.
Such low level flight after ta~e-off is hazardous ~ecause if the pilot ~ecomes distracted or disoriented, he may inadvertently allow the aircr~ft to descend into the ground or water. Such disorientation is part$cularly likely at night over water or in otber areas where the pilot may lose visual reference after take-off and allow the aircraft to descend into the ground or water. Consequently, it is desirable to provide the pilot with a sensitive warning system that alerts him of an excessive descent after take-off. A sensitive system is particularly necessary because of the low altitude at which &uch aircraft fly. ~owever, after take-off, such aircraft may engage in maneuvers that will cause warnings to ~e qenerated, even though the maneuvers being engaged in are inten-tional rather than inadvertent. One way to eli~lnate or reduce the frequency of occurrence of such nuisance ~Z434~3 t~

warnings is to ~ake the system less ~ensitive. Another way i~ to set the altitude above which the sy-tem is disa~led to an altitude that is ~elow th2 normal maneuvering altitude. However, neither of these approaches is entirely satisfactory ~ecau~e desen-sitizing the system will delay the warning and may not g~ve the pilot 6ufficient warning time in the event of an inadvertent descent after ta~e-off.
Lowering the altitude above which a warning cannot be generated also poses problems, ~ecau~e if an inadver-tent descent occurs at a higher altitude, no warning will be given.
Thus, the system according to the invention utillzes not only altitude, but al80 the length of time that the aircraft has ~een flying in order to determine the warning criteria. In the system accord-ing to the pre~ent invention, the ~ystem is ~tructured to be ~ost ~ensitive i~mediately after ta~e-off when the aircraft is at low altitude and very little time into the flight has elapsed. The ~ystem i8 then desensitized both AS a fun~tion of altitude and elapsed time into the flight, that is, the timé-altitude pro-duct. Thus, at bigher altitudes, greater descents are permitted before a warning is generated. Similarly, ~s ~ore flight time el~pses, and the pilot has had an opportunity to orient him elf, greater descents are permitted until the system is di~a~led when enough alti~ude and/or flight tlme has been accumulated to indicate that this warning mode is no longer required.
Because barometric altitude is used to generate the time-altitude product, a valid radio altitude signal is not required for the system to operate. This is particularly advantageous for aircraft that have radio altimeters that have long loc~-on times, th~t is, ~Z~3~

that do not provide a valid radio altitude signal until ~everal seconds after ta~e-off.
I--L~I,U~_L~Dc~ WING
These and other objects and advantages of the present invention will become readily apparent upon consideration of the following detailed descrip-tion and attached drawing, wherein:
FIG. 1 is a functional ~loc~ diagram of a warning system built in accordance with the principles of the present invention; and FIG. 2 is a graph illustrating the relation-~bip between the time-altitude product and the altitude loss required for a warning to be generated.

A ~ystem according ts the invention capable of pr~v~ding the warning functi~n describ~d a~ove is illustrated in FIG. 1, and designated generally ~y the reference numeral 10. The system according to the invention is illustrated in FIG. 1 in functional or logical ~loc~ diagram form as a series of gates, c~mparator~ and the li~e for purposes of ~llustration;
however, it should ~e understood that the actual implementation of the logic can be otber than as shown in FIG. 1, with various digital and analog implemen-tations being possible. The signals used ~y the warn-ing syYtem as descrlbed include radio altitude, baro-~etric altitude, ~arometric altitude rate, signals representative of the positions of the flaps and land-ing gear, ~ign~ls representative of take-off power and whether the aircraft is in the take-off mode, a signal indicating whether there i~ any weight on the wheels and various validity signals. Depending on the type of aircraft in which the warning system is installed, the signals shown in FIG. 1 can be o~t3ined from individual instruments such as a ~aro~etric alti-3LZL~3~L17 meter 12, a barometric ~ltitude rate circuit 14, a radio altimeter 16, and from discrete elements indicat-ing whether the aircraft is in a ta~e-off ~ode of flight, whether there i8 any weight on the wheels, S and whether the flaps and landing gear are up or down.
Also, a vertical velocity signal ~uch as the 2-velocity signal from an inertial navigation ~ignal may ~e used to provide the ~ltitude rate signal instead of the barometric rate circuit. In certain newer aircraft the data may ~e received from a digital data ~us.
The output of the radio altimeter 16 is ~pplied to a sample and hold circuit 1~ ~ia a switch 20 that i5 cloBed only when the signal from the radio ~ltimeter i~ valid. The output of the ~ample and hold circuit 1~ is connected via a ~wltch 22 to a ~umming junction 24 and to a scallng circuit 26 whose output is connected to a second summing junction 2~.
The output of the barometric rate circuit 14 i8 applied to an integrator 3U whose output i5 applied to the ~umming junction 24. The output of the ~ = ing junc-tion 24 i~ applied to a second integrator 32 whose output is summed via junction 28 and coupled to a co~parator 34. The output of the comparator 34 is coupled to an AND gate 36 whose output controls an aural warning generator 38 via delay circuit 3Y that ~n turn operates ~ transducer 40.
Another one of the inputs of the AND gate 36 $s coupled to the output of an ~ND gate 42 that also serves ~o ena~le the integr~tors 30 and 32. The AND gate 42 receives a n~ weight on wheels signal from a discrete 44 via a delay 46, a barometr~c alti-meter valid signal from the ~arometric altimeter 12 and a take-off mode signal from ta~e-off ~ode logic circuitry 48 that is standard on ground proximity J35 warning systems such as the Mar~ II Ground Proximity ~l2~3 Warning System manufactured by Sunclstrand Data Control, Inc. The fourth input to the AND gate 42 is from a three-input OR gate SO that receives signals from a flap up discrete 52, a gear up discrete 54 and a take-off power latch circuit 56. ~he ta~e-off power logic and lat~hing circuit 56 ma~ be, for example, a circuit that monit~rs the tachometer of one or more of the engines of the aircraft and provides a take-off power signal when the RPM of one or more engine is such ~hat take-off power i8 indicated, and main-tains that 8~ gnal irrespective of power lo~ses until uch a time that other predetermined conditions exist which will clear the signals.
The tbird output of the AND gate 36 is coupled to the output of a descent comparator 5~ that compares the output of the barometric rate circuit 14 with a reference aignal represen~tive of zero feet per ~econd obtained from a reference source 60~
Another integrator 62 integrates the barometric rate signal from the barometric rate circuit 14 and applies the integr~ted signal to one of the inputs of the co~parator 34 via a summing junction 64 which also receives a signal repre~entative of ten feet of alti-tude from ~ reference circuit 66. The output of the integrator 62 ~s ~lso coupled ~o another comparator 68 which compares the output from the integrator 62 with a s$gnal repre~entative of zero feet of altitude received from a reference circuit 69. The ou~put of tbe comparator 68 is coupled to an OR gate 70 that has another input coupled to the output of the descen~
comparator 58-and an output coupled to an AND gate 72. Another input of the AND gate 72 is coupled to the output of the AND gate 42, and the output of the AND gate ~2 i~ coupled to an enable input of the inte-grator 62.

3~i'7 In operation, and assuming that the signals from the barometric altimeter 12 and the radio alti-meter 16 are valid, the system is ena~led ~y the AND
gate 42 only when certain conditions are met. More specifically, the system is enablecl only when there has ~een no weight on the wheels for more th~n 2 seconds and the aircraft is in the ta~e-off mode and if the taKe-off power latch is 8et or the landing gear is up or the flaps are up. The delay circuit 46 delays the enabling of the cystem for approximately two seconds to permit the ~arometric altimeter signal to stabilize after t3~e-off.
When the aforementioned conditions are met, the AND gate 42 applie~ ena~ling ~ignals to the AND
lS gates 36 and 72, to the integratorfi 30 and 32, and to the Qample and hold circuit lB and switch 22. Thus, upon ena~ling of the integrators 30 ~nd 32, the Daro-metric rate signal or other appropriate vertical velo-city ~ignal is integrated ~y the integrator 30 to provide 2 signal representative of altitude gain or loss. This signal ls again integrated with respect to time ~y the integrator 32 to provide a time-altitude or feet-second~ signal. Aleo, immediately after ta~e-off, and after the AND gate 42 i8 ena~led, the output of the ~ample ~nd hold circuit 1~ is com~ined with the output of tbe integrator 30 to provide an altitude a~ove ground reference signal for the output of the integrator 30. In the event that the radio altitude signal is not present, for example during a loss of trac~ condition, the output of the sample and bold circuit 18 is zero feet, there~y assuming ground level reference. In addition, the output signal from the sample and hold circuit 1~ is multiplied ~y a scaling factor such as, for example, 104, by the scaling cir-cuit 26 to provide a reference for the output of the ~2~3:1~'7 g integrator 32. ~he comb1ned feet-seconds signal from the integrator 32 and the scaled referen~e signal from the scaling circuit 26 are combined and applied to the warning comparator 34 to be compared with the output from the in~egrator 62 received via the suDing junction 64.
The combined effect if these circuits is to provide a true indication of accumulated feet-seconds of time-altitude when the system is initialized at some altitude a~ove ground or sea level a might ~e the case in a missed approach, for example. The sampled radio altitude operates to include the initial altitude a~ove ground or sea level in the time-altitude integra-t$on and also to increase the initial altitude loss required for a warning from 10 feet to 10 feet plus 10 per cent of current radio Dltitude, a value more consistent with conventional radio altitude ~ased systems.
The integrator 62 integrates the output from the barometric rate circuit 14 to provide a signal representative of accumulated altitude 10s8 after ta~e-off. This occurs because tbe integrator 62 i8 ena~led only when the ~ircraft is descending, or when an altitude loss ha~ already occurred. The enabling function ~s ~ccomplished ~y the descent rate comparator 58 and t~e co~parator 68. The descent rate comparator 5~ compares the descent rate signal from the ~aro-metric rate circuit 14 with a zero feet per ~econd reference si~nal from the reference source 60, and provides an ena~ling signal to the integrator 62 via the gates 70 and 72 only if the aircraft is descending.
The comparator 6 compares the output of the integratoc 62 with a zero foot reference signal and maintains the integrator 62 ena~led as long as the output of the integra~or 62 is representative of an accumulated ~L2 ~311 ~

altitude 105s. Thus, once ena~led after an initial descent, the lntegrator 62 is maintained enabled until all of the lost altitude has been regained. The alti-tude loss signal is offset ~y 10 feet ~y the ~umming circuit 64 and applied to the comparator 34. Because of the 10 foot offset, the aircraft must descend at least 10 feet before any warning will be given to thereby minimize nuisances.
The comparator 34 thus compares the accumu-lated ~ltitude lo~s from the comparator 6~ with thetime-altitude or feet-~econds signal from the inte-grator 32 and provides a warning initiation signal to the gate 36 if the barometric altitude loss is exces-sive for the time-altitude product of the aircraft.
Thi~ relationship is illu~trated in FIG. 2. As is apparent from FIG. 2, during lo~ altitude~ or during the inltial pha~es of flight when the time-altitude proBuct i8 small, only 10 feet of altitude loss is permitted before a warning is generated. However, as the time-altitude product increases, the permitted altitude 108s also increases until an altitude loss of 310 feet is permitted at a time-altitude product of 37,500 feet-~econds. A~ove 37,500 feet-~econds, the system i8 effectively disabled until the next e~e-off or the next go-~round after a missed ~pproach.
As was previously discussed, an ~ural warning informing the pilot of a h~z~rdous condition has been found to be quite effective, and in the present em~odi-ment, the gate 36 is used to cause the aural warning generator to generate a message such as ~DON'T SINK"
after an appropriate delay, for example 0.8 seconds, ~hich ~erves to ignore momentary altitude loss excur-sion~ caused by signal noise. The message thus generated is applied to the transducer 40, wh$ch may ~e a loudspea~er or a pair of headphones, either ~24311~7 directly or indirectly through the intercommunication system of tbe aircraft.
O~viously, many modifications and variations of the present invention are possible in light of the a~ove teachings. Thus, it is to ~e understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically des-cri~ed above.

Claims

1. A warning system for providing a warning of a hazardous flight condition to the pilot of an aircraft during a take-off or a go-around after a missed approach phase of flight, comprising:
means for providing a signal representative of the altitude loss from an altitude peak reached during flight;
means for providing a time-altitude signal that is a function of the altitude of the aircraft and the length of time that the aircraft has been flying; and means responsive to the altitude loss re-presentative signal and said time-altitude signal to provide a warning in the event that the altitude loss representative signal is excessive for the current value of the time-altitude signal.

2. A warning system as recited in claim 1 wherein said time-altitude signal providing means includes means responsive to the altitude rate of the aircraft for generating the time-altitude signal.

3. A warning system as recited in claim 2 wherein said altitude rate signal is a barometric rate signal.

4. A warning system as recited in claim 2 wherein said altitude rate signal is a vertical velo-city signal.

5. A warning system as recited in claim 2 wherein said time-altitude signal providing means includes means for integrating the altitude rate signal to provide the altitude signal.

6. A warning system as recited in claim 5 wherein said time-altitude signal providing means includes means for integrating the altitude signal.

7. A warning system as recited in claim 6 wherein said time-altitude signal providing means includes means responsive to a signal representative of the radio altitude of the aircraft for sampling the radio altitude signal and combining the sampled radio altitude signal with the altitude signal.

8. A warning system for providing a warning of a hazardous flight condition to the pilot of an aircraft during take-off or a go-around after a missed approach phase of flight, comprising:
means for providing a signal representative of the altitude rate of the aircraft;
means responsive to said altitude rate signal for twice integrating the altitude rate signal to provide a time-altitude signal;
means responsive to said descent rate signal for providing a signal representative of the accumulat-ed altitude loss from an altitude peak attained by the aircraft; and means for comparing the time-altitude signal and the altitude loss signal and initiating a warning in the event of an excessive altitude loss relative to the value of the time-altitude signal.

9. A warning system as recited in claim 8 further including means for generating a signal repre-sentative of the altitude of the aircraft above ground and means for combining the altitude above ground signal with the time-altitude signal to modify the value of the time-altitude signal applied to the comparing means.

10. A warning system as recited in claim 9 wherein said time-altitude signal providing means includes means responsive to a signal representative of the radio altitude of the aircraft for sampling the radio altitude signal and combining the sampled radio altitude signal with the altitude signal.

11. A warning system as recited in claim 8 wherein the altitude rate signal is a barometric descent rate signal.

12. A warning system as recited in claim 8 wherein the altitude rate signal is a barometric signal.