Note: Descriptions are shown in the official language in which they were submitted.
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1 This application is a division of application
serial number 449,619, filed March 14, 1984.
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates generally to ground
proximity warning systems, and more particularly to a system
that protects an aircraft during low altitude maneuvers if
the aircraft should descend below a predetermined minimum
altitude above ground, or if the aircraft exceeds a
predetermined descent rate while performing turning
maneuvers or other maneuvers requiring a roll. Distinct
,pecific warnings are given in order to inform the pilot of
~he specific action that must be taken to recover from a
~angerous flight profile.
Description of the Prior Art
Ground proximity warning systems that warn a pilot
of a dangerous flight profile are known. These systems
provide warnings to the pilot of an aircraft under various
unsafe flying conditions including flying below a preset
minimum altitude, and permitting the aircraft to attain an
excessive descent rate after take-off or on approach. An
~sxample of a system that provides a pilot with a warning if
he drops below a predetermined minimum desired altitude is a
system that compares the radio altitude with the minimum
decision altitude setting, or "bug" setting on the radio
altimeter, and provides an aural or visual warning if the
radio altitude drops below the set minimum decision
altitude. Examples of systems that provide a warning to a
pilot during a take-off or a missed approach phase of
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operation if the aircraft should descend at an excessive
barometric rate or lose a predetermined amount of
barometric altitude are disclosed in United States patent
Nos. 3,946,358; 3,947,808, 3,947~810 and 4,319,218;
assigned to the same assignee as the present invention.
While these systems serve to provide the
pilot with a warniing in the event that the aircraf~
drops below a preset minimum desired altitude above
ground, or if the aircraft descends excessively after
take-off or a missed approach, such svstems are designed
primarily for transport aircraft that do ~ot normally
fly at low altitudes or execute turns or other severe
or violent maneuvers near the groundD Conseouently,
such systens would not normally provide adequate warn-
ing to the pilot of a highl~ maneuvera~le aircraftsuch as, fc)r example, a fighter/attack aircraft execut-
ing tactical maneuvers near the ground.
SUMMA~Y OF TEE INVENTION
l~ccordingly, it is an object of the present
invention 1:o provide a warning system that overcomes
many of the disadvantages of the prio~ art warning
systems during high speed, low level naneuvering phases
of aircraft operation.
[t is another o~ject of the present invention
to provide a warning system ~esigned to provide the
piaOt of a high performance aircraft such as a
fighter/attack aircraft cruising at low altitude with
a warning indicating a dangerous flight condition in
sufficient time to perm~t him to take corrective
action.
~ t is another object of the prese~t in~en-
tion to provide the pilot of an aircraft executing
turning and banking maneuvers near the ground with a
warning of a dangerous condition such as an excessive
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descent rate in sufficient time to permit the pilot
to take corrective action.
It is yet another object of the present
invention to provide a warning of an excessive radio
altitude loss during take-off into rising terrain.
The mission flight profile of a
fighter/attack aircraft contains low altitude cruise
and attack segments, and if the pilot becomes dis-
tracted or disoriented, there is a danger of inadver-
tent descent into terrain or flight into slowly rising
terrain. The danger of flying into rising terrain
exists primarily during take-off, and during low alti-
tude cruise. The danger of inadvertent descent is
greatest during low level maneuvers requiring high
roll angles, such as are encountered during an attack
portion of a flight, because the pilot can easily
become distracted and disoriented during such maneuvers,
and because aircraft tend to sink when they are suk-
jected to high roll angles.
Therefore, in accordance with a preferred
embodiment of the invention, there is pxo~ided a warn-
ing system that senses the altitude of the aircraft
above the ground utilizing a radio altimeter or the
like, and provides a specific aural warning, such as
"TOO LOW" to the pilot if the aircraft descends below
a predetermined minimum desired altitude above ground,
thereby providing protection during low altitude cruise
phases of operation. The predetermined minimum
desired altitude is typically the minimum decision
altitude which is manually set by the minimum decision
altitude marker or altimeter "bug" present on a radi~
altimeter indicator.
Also, in order to provide a warning during
take-off into rising terrain, or during an inadvertent
descent before the minimum decision altitude is reached,
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the system is provided with an accumulator that
monitors the radio altitude after take off and stores
the highest altitude reached after take-off. In the
event that the aircraft descends below a predetermined
percentage of the maximum radio altitude reached prior
to reaching the minimum decision altitude, a warning
is also generated. Typically, this warning will be
the same "TOO LOW" warning that is generated if the
minimum decision altitude is ~enetrated in order to
indicate to the pilot that he is too low.
In additionf the system monitors the roll
angle of the aircraft and generates a second specific
warning in the event that the aircraft is below a
second predetermined altitude r and exceeds a predeter~
mined descent rate which varies as a function of the
roll angle of the aircraft in order to warn the pilot
that the aircraft is descending at an excessively
high rate during a roll maneuver~ The warning given
should be specific enough to enable the pil~t to
diagnose the problem quickly, and in the present
embodiment, a warning such as the warning ~ROLL OUT"
- or similar term is provided.
DESCRIPTION OF THE DRAWING
These and other objects and advantagec; of
the present invention will become apparent upon con-
sideration of the following detailed description and
attached drawing, wherein:
FIG. 1 is a logical block diagram of the
warning system according to the invention;
FI~c 2 is a graph illustratin~ the relation-
ship between airspeed and radio altitude where warnings
may be generated; and
FIG. 3 is a graph showing the relationship
between barometric altitude rate and roll angle required
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to generate a warning that the aircraft is descending
at an excessive rate during a roll maneuver.
DETAI LED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawing, with particular
attention to FIG. 1, there is illustrated an embodiment
of a ground proximity warning system according to the
invention particularly useful for providing warnings
of unsafe flight conditions during low level maneuver-
ing generally designated by the reference numeral 10.
The system 10 according to the invention is illustrated
in FIG. 1 in functional or logical block diagram form
as a series of gates, comparators, flip-flops and the
like for purposes of illustration; however, it should
be understood that the actual implementation of the
~5 logic can be other than as shown irl FIG. 1, with various
digital and analo~ implementations being possible~
The signals used by the warning system as described
include radio altitude, barometric altitude rate,
airspeed, engine RPM, roll angle of the aircraft, the
minimum decision altitude and signals indicating the
position of the aircraft landing gear along with various
validity signals. Depending on the type of aircraft
in which the warning system is installed, th~ signals
shown in FIG~ 1 can be obtained from individual instru-
ments such as a barometric altimeter 12, a barometricaltitude rate circuit 14, a radio altimeter 16 and a
gyroscopic platform 18, as well as various discrete
circuit elements such as a discrete elem~nt indicating
the position of the landing gear. These signals may
also be obtained from a digital data bus in certain newer
aircraftO
As previously stated, the system according
to the invention is designed to pr~vide different
warnings during different phases of aircraft operation.
For example, the system is designed to provide a irst
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warning, such as, for example, an aural or voice warn-
ing ~TOO LOW" should the aircraft descend below the
minimum decision altitude during low level cruise.-
This warning will also be generated if the aircraft
should lose a predetermined percentage of the altitude
attained after take-off, but prior to reaching the
minimum decision altitude. In addition, the system is
designed to provide a second specific warning, such
as, for example, the aural or Yoice signal "ROLL OUT~
should the aircraft descend too rapidly during a roll
maneuver~ Consequently, logic circuitry is provided
to indicate to the system the particular flight phase
in which the aircraft is operating, i.e~, take-off,
low level cruise or low level maneuvering so that the
appropriate warning will be generated should cer~ain
flight parameters be exceeded. This function is pro-
vided by the logic circuitry including AND gates 20,
22, 24, 26, and 28, an OR gate 30, a pair of set/reset
flip-flops 32 and 34, a transition detector 36 and a
switch 38 controlled by the flip-flop 34.
Because the system is designed to be opera-
tional to provide warnings during take-off, low level
cruise and low level maneuvering phases of flight,
certain determinations must be made to determine
whether the aircraft ii indeed in one of the aforemen-
tioned phases. The initial determinations are made
by the AND gate 20 which provides an enabling signal
to the AND gates ~2 and 24 only if certain conditions
are met. These conditions are that there is no weight
on the wheels, indicating that the aircraft is actually
flying, that the gear is up and the aircraft is not
flying slower than 200 knots, thereby indicating that
the aircraft is not in a landing configuration. Also,
for the system to be operational, the barometric alti-
meter 12t the barometric rate circuit 14 and the radio
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altimeter must be operating properly. Consequently,signals indicating that the barometric altimeter and
radio altimeter have not been inhibited, as well as
a signal indicating that the rate of the radio
altitude is not excessive are applied to the gate 20
to cause the gate 20 to enable the gates 22 and 24
only if the signals from the barometric altimeter
12, the barometric rate circuit 14 and the radio
altimeter 16 are valid.
In addition to detel-mining whether the air~
craft is flying in a configuration other than a land-
ing configuration and that the instruments are operat-
ing properly, it is necessary to determine whether
the aixcraft is in an approach phase, or in a take-
off or a go-around after missed approach phase, This
determination is made by the gates AND ~6 and 28, the
OR gate 30 and the set/reset flip-flop 32. In the
implementation shown, a take-off or a go-around after
a missed approach is indicated only if both the condi-
tions that take-off power is present and that the
~anding gear is up are met. If both corlditions are
met, the set/reset flip-flop 32 is reset. Signals
indicative ~f take-off power ~hat are applied to the
gate 26 can be obtained from various sources, for
example, from a comparator circuit that provides an
enabling signal to the gate 26 when the RPM of the
engine is sufficiently high to indicate take-off power,
or from a discrete element indicating thxottle posi-
tion. An engine tachometer, which indicates for
example~ the RPM of the ~rimary compressor of a jet
engine~ can be used to provide the engine RPM signal,
and a predetermined RPM, for example, 90% of maximum
engine RPM, can be used to indicate take-off power.
The gear up signal can readily be obtained from another
discrete element, such as, from a switch operated by
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the landing gear or by the landing gear control handle
in the cockpit.
An approach condition is indicated by the
gates 30 and 28 when the gear is not up or the aircraft
is below 100 feet and the engine is not producing
take-off power and the speed of the aircraft is below
200 knots. An approach condition indication from the
gate 28 serves to set the flip-flop 32.
In operation, during the take-off phase of
flight, the set/reset flip-flop 32 is reset, thereby
causing the Q output of the flip-flop 32 to change
from a high state to a low state. This transition is
detected by the transition detector 36 which generates
an output pulse in response to the transition and
sets a set~reset flip-flop 34. This causes the Q
output of the flip-flop 34 to operate the switch 38
to the position shown in FIG. ~, thereby to connect
one input of the gate 2~ to circuitry including a too
low comparator 40, a scaling circuit 42 and a radio
altitude accumulator 44. These devices determine
when a "~OO LOW" warning should be generated by a
generator 46 during the take-off mode of operation.
After the aircraft has completed its take-
off, as evidenced by the radio altitude exceeding the
minimum decision altitude (MDA), an MDA comparator 50
provides a signal indicating that the aircraft has
exceeded the minimum decision altitude in order to
reset the input of the flip-flop 34, thereby resetting
the flip-flop 34. When the flip-flop 34 is reset,
the switch 38 is operated to disconnect the gate 22
from the too low comparator 40 and connected to a
LESS THAN MDA output of the ~DA comparator 50, thereby
making the system responsive to any descents below
the minimum decision altitude. Consequently, if the
aircraft drops below the minimum decision altitude
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when in this mode, the warning generator 46 will gener-
ate the ~TOO LOW" warning and apply it to the trans-
~ucer 48.
As long as the altitude of the aircraft is
below the minimum decision altitude plus a predeter-
mined increment, such as, for example, 100 feet, but
not below the minimum decision altitude, the AND gate
24 is enabled by the comparator 50 via the GREATER
T~AN MDA and LESS ~HAN MDA I 100 FEET signals applied
to two of its inputs. When so enabled, the AND gate
24 is made responsive to a pair of comparators 52 and
54 to operate a second warning generator 56 which
generates a second warning such as, for example, ~ROLL
OUT" when the descent rate of the aircraft exceeds a
predetermined level for a given rolt angle.
Discussing the operation in greater ~3etailt
as the aircraft takes off, the flip-flop 32 is reset,
thereby causing the transition detector 36 to ~?rovide
an output pulse to set the flip-flop 34 to thereby
connect the gate 22 to the comparator 40. The output
pulse from the transition detector 36 also re~ets the
radio altitude accumulator to zero, or to a predeter-
mined low value setting~ such as, for example, 50
feet. The radio altitude accumulator receives the
altitude signals from the radio altimeter 16, and
retains the highest altitude reached since take-off.
This maximum value of radio altitude reached since
take-off is applied to a scaling circuit which multi-
plies by a scaling factor, for example, 75% and applies
to the too low comparator 40 which controls the opera-
tion of the too low warning generator 46 during the
take-off phase of operation.
The radio altimeter signal is also applied
to the too low comparator 40, and as long as the
radio altitude remains above the maximum radio altitude
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multiplied by the scaling factor, no warning is gener-
ated. However, if the radio altitude drops below the
scaled maximum altitude/ for example, below 75% of
the maximum altitude reached during the flight, the
comparator 40 will provide a signal to the gate 22.
This signal will cause the gate 22 to provide a signal
to the "TOO LOW" warning generator 46 and cause the
generator 46 to generate the ~TOQ LOWn warning and
apply it, either directly or indirectly, to the trans-
ducer 48, provided that the other input of the gate22 is enabled by the gate 20. The radio altitude signal from the altimeter
16 is also applied to the MDA comparator 50 which monitors
the radio altitude signal ffom the radio altimeter 16
and provides a GREATER THAN MDA signal to the flip-
flop 34 when the radio altitude exceeds the minimum
decision altitude. ~his signal resets the flip-flop
34 and causes the switch 38 to connect the gate 22 to
the MDA comparator 50 so that any warning generated
will be controlled by MDA comparator 50. ~he MDA
comparator 50 continues to monitor the radio altitude,
and no warning is initiated as long as the radio altitude
remains above the minimum decision altitude. However,
if the altitude drops below the minimum decision altitude
and the gate 22 is enabled by the gate 20, the MDA com-
parator will provide a LESS THAN MDA signal to the
gate 22 to cause the gate 22 to initiate the ~TOO
LOW" warning by the warning generator 46.
As the aircraft climbs above the minimum
decision altitude, but remains below the minimum
decision altitude plus a predetermined increment,
such as, 100 feet and as long as the gate 20 provides
an enabling signal, the gate 24 will be under the
control of a roll-out comparator 52 and a roll angle
comparator 54. The function of the comparators 52
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and 54 is to monitor the roll angle and barometric
descent rate of the aircraft, and to cause the gate
24 to initiate a warning by the warning generator 56
if an unsafe combination of descent rate and roll
angle exists.
As previously discussed, aircraft tend to
descend as the roll angle is increased. However,
this tendency is not significant until the roll angle
exceeds a predetermined level; such as, for example,
}o 45 for modern fighter/attack aircraft such as the
Fairchild A10. Consequently, the roll angle compara-
tor 54 monitors the roll angle signal generated by
the gyro platform 18, or similar device indicating
the roll angle of the aircraft, and provides an
enabling signal to the gate 24 when the roll angle
reaches the roll angle at which the aircraft tends to
sink. This permits the "ROLL OUT" warning to be
generated by the generator 56 if the barometric
descent rate exceeds the maximum rate permitted for a
given roll angle, as determined by the roll-out com-
parator S2. The conditions necessary for the "ROLL
OUT" warning to be generated are further discussed in
connection with the discussion of FIG. 3.
Referring to FIG. 2, there is shown a graph
illustrating the conditions necessary to generate the
"TOO LOWn warning and to enable the "ROLL OUT" warning
as a function of airspeed and altitude. These condi-
tions are illustrated by the two shaded areas on the
graph. As is apparent from FIG. 2, neither warning
can be generated as long as the airspeed of the air-
craft is below a predetermined value, in this embodi-
ment 200 knots. As long as the airspeed of the air-
craft exceeds 200 knots, and the other previously
discussed conditions are met, the 'iTOO LOW" warning
will be given whenever the aircraft drops below the
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minimum decision altitude, or below a predetermined
percentage, for example 75%, of the maximum altitude
reached on take-off or go-around prior to exceeding
the minimum decision altitude.
When the altitude of the aircraft exceeds
the minimum decision altitude, but is below the mini-
mum decision altitude plus a predetermined increment,
such as, for example, 100 feet, the ~ROLL OUT" warning
is enabled. However, the "ROLL OUT" warning is not
automatically generated when the "ROLL OUT" warning
boundary illustrated in FIG. 2 is penetrated, as is
the case when the "TOO LOW" warning boundary is pene-
trated. Rather, the ~ROLL OUT" warning mode is only
enabled, but the actual warning is produced only if
the roll angle exceeds a predetermined angle, for
example, 45, and if the descent rate penetrates the
boundary of the descent rate curve (~IG. 3) which
defines the maximum permissible descent rate as a
function of roll angle.
A descent rate curve which has been found
to be particularly suitable for use in fighter/attack
aircraft is illustrated in FIG. 3. The shaded area
shows the relationship between roll angle and baro-
metric descent rate necessary to generate the ~ROLk
OUT" warning. As can be seen from FIG. 3, the "ROLL
OUT" warning is not generated until the roll angle
reaches 45, at which point the "ROLL OUT" warning is
generated if the barometric altitude descent rate
exceeds 100 feet per minute. As the roll angle is
increased to 60, only 50 feet per minute of descent
rate is required to initiate a warning, and when the
roll angle reaches 90, no descent at all can be
tolerated because the lif t provided by the wings
under this condition is virtually zero.
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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 des-
cribed above.
