Negative climb after take-off warning system with configuration warning means

During a take-off or missed approach phase of operation the aircraft's maximum barometric altitude is retained in a memory element and compared to the aircraft's current altitude, and if the aircraft's current barometric altitude should be below the maximum altitude by a predetermined amount based on the aircraft's radio altitude, a voice warning is generated indicating that the aircraft is descending. Landing gear and flaps are monitored by the system and if the gear or flaps are down, an additional voice warning is generated indicating that the gear or flaps are down.

TECHNICAL FIELD 
The invention relates to the field of aircraft ground proximity warning 
systems and, in particular, to systems that warn of aircraft descent after 
take-off or during a missed approach. 
BACKGROUND OF THE INVENTION 
In prior art ground proximity warning systems such as the systems disclosed 
in U.S. Pat. Nos. 3,946,358 and 3,947,810, warnings are generated during a 
take-off or a missed approach phase of operation if the aircraft should 
descend at a predetermined barometric rate or lose a predetermined amount 
of barometric altitude prior to reaching a predetermined altitude such as 
700 feet. The object of the warning is to prevent the flight crew from 
flying the aircraft back into the terrain directly after take-off or 
during a missed approach maneuver. Such accidents have occurred during 
periods of reduced visibility when the flight crew is unable to determine 
from outside visual references that the aircraft is descending. Ground 
proximity warning systems in use today will typically generate a voice 
warning in this type of situation with the voice warning consisting of the 
words "whoop-whoop", "pull-up" or "don't sink". This type of voice warning 
is normally adequate to provide a pilot with sufficient warning that the 
aircraft is inadvertently descending after take-off although the warning 
"don't sink" is considered to be better than "pull-up" since it provides 
the pilot with more specific information as to the nature of the hazzard 
faced by the aircraft. However there are situations in which it may be 
highly desirable to provide the pilot with more specific information as to 
the aircraft's actual condition. For example, during a take-off phase of 
flight if an engine should fail the aircraft may not be able to climb and 
may actually lose altitude when it is in certain flight configurations. 
There are certain aircraft types that under certain conditions such as an 
engine out configured with the landing gear down or with landing flaps 
down are unable to gain altitude and in fact will tend to lose altitude. 
Under these circumstances a simple warning of "pull-up" or "don't sink" 
may not provide the pilot with any useful information since he may 
understand quite well that he is descending but what he may not realize is 
that the reason he is descending is that the aircraft is not in the proper 
configuration for an engine out condition. It should be noted that in 
addition to the landing gear and flaps, flight configuration of an 
aircraft could include a number of other elements such as leading edge 
slat extensions and trim considerations. There have been incidents where 
the flight crew upon losing an engine during take-off have not realized 
that the landing gear was in an extended condition due to the large amount 
of work in the cockpit connected with a return to the airport under 
emergency conditions. 
Prior art negative climb after take-off warning systems that utilize an 
actual loss of barometric altitude after take-off to generate a warning 
such as disclosed in U.S. Pat. No. 3,947,810 use an integrator to 
integrate barometric descent rate to get the measure of altitude loss. The 
integration of a barometric rate signal can lead to errors based on 
integrator drift or the nature of the barometric signal used. 
SUMMARY OF THE INVENTION 
It is therefore an object of the invention to provide a negative climb 
warning system that provides a specific warning to the flight crew of 
aircraft configuration as well as a warning that the aircraft is 
descending after take-off. 
It is another object of the invention to provide a negative climb warning 
system that will generate a warning to the pilot that the landing gear is 
down if the aircraft is descending after take-off with the gear down and 
will also generate a warning to the pilot that the flaps are down if the 
aircraft is descending after take-off with the flaps down. 
It is a further object of the invention to provide a negative climb warning 
system with logic elements responsive to the landing gear condition and 
the flap condition in order to generate a "gear" voice warning or a 
"flaps" voice warning in addition to a "don't sink" voice warning when the 
aircraft is descending in a take-off or missed approach phase of 
operation. 
It is an additional object of the invention to provide a ground proximity 
warning system for aircraft which will generate a warning when the 
aircraft descends during take-off responding to signals representing the 
configuration of the aircraft, signals indicating the phase of flight such 
as take-off, missed approach or landing and a signal indicating that the 
aircraft is descending wherein a first warning signal is generated when 
the aircraft is descending and a second type of warning signal is 
generated when the aircraft is descending in a predetermined 
configuration. 
Still another object of the invention is to provide a negative climb 
warning system that responds to signals representing the barometric 
altitude of the aircraft, signals representing the aircraft configuration, 
and signals representing the aircraft's phase of flight having an 
electronic memory circuit that stores in response to the operation of a 
first logic circuit the maximum barometric altitude that the aircraft has 
achieved during the take-off phase of operation and a second electronic 
logic circuit responsive to the first logic circuit for generating a 
warning signal when the current aircraft barometric altitude is less than 
the barometric altitude stored in the memory circuit and a circuit for 
generating a voice warning indicating that the aircraft is descending. 
In order to provide the flight crew with more specific information when the 
aircraft is descending during a take-off phase of operation, the warning 
system is responsive to the condition of the landing gear and the flaps to 
generate additional voice warnings indicating that either the landing gear 
is down or the flaps are down in combination with a voice warning 
indicating that the aircraft is descending. 
The system for determining whether or not the aircraft is descending during 
the take-off or missed approach phase of operation includes a memory 
element that responds to a signal indicating the aircraft's current 
barometric altitude. As the aircraft continues to climb, the altitude 
stored in the memory element is continuously updated thereby providing a 
reference for the aircraft's maximum altitude. However if the aircraft 
should begin to descend, logic elements are provided in the warning system 
to compare the aircraft's current barometric altitude with the barometric 
altitude stored in the memory element and a warning is generated if the 
difference between the current altitude and the maximum altitude exceed a 
predetermined amount. The amount of altitude required to generate a 
warning will vary as a function of radio altitude which is also used as an 
input to the system. The amount of difference between the maximum 
barometric altitude and the current barometric altitude before a warning 
is given will increase as a function of increasing radio altitude such 
that the aircraft is allowed to descend more when it is higher above the 
ground.

DETAILED DESCRIPTION OF THE INVENTION 
In FIG. 1 is illustrated in block diagram form the logic of the preferred 
embodiment of the invention. A source of signals or data source for the 
negative climb after take-off warning system is shown in block 10 of FIG. 
1. The signals used by the warning system as described include radio 
altitude, barometric altitude, barometric altitude rate and signals 
indicating the position of the aircraft's landing gear and flaps along 
with various validity signals. Depending upon the type of aircraft in 
which the warning system is installed, the signals shown in block 10 can 
be obtained from individual instruments such as a radio altimeter, a 
barometric altimeter or discreet circuit elements indicating the position 
of the gear and flaps or in the case of some of the newer commercial 
aircraft some or all of this information is available on a digital data 
bus. 
In order to determine whether or not the aircraft is losing barometric 
altitude, the barometric altitude signal h.sub.B is transmitted from the 
data source 10 on line 12 to a filter 14. The filter 14 with preferably a 
time constant on the order of two to three seconds filters out the 
short-term variations in the barometric altitude signal. The filtered 
barometric altitude signal is then transmitted on line 16 to a latch 
circuit or electronic memory circuit 18 which serves to store the value of 
the aircraft's barometric altitude. The latch circuit 18 shown in FIG. 1 
can be an analog latch circuit serving to hold a voltage representing 
aircraft altitude or could be an electronic memory or register serving to 
hold a digital representation of aircraft altitude. The value of the 
barometric altitude stored in the memory element 18 h.sub.Bmax represents 
the maximum barometric altitude that the aircraft has achieved during the 
take-off phase of operation and h.sub.Bmax is transmitted over line 20 to 
a positive terminal of the summing element 22. The value of the current 
barometric altitude h.sub.B on line 16 in then applied to a negative 
terminal of summing element 22. Radio altitude information h.sub.R which 
is usually derived from a radio altimeter and represents the aircraft 
altitude above ground is transmitted from the data source 10 over line 24 
to a multiplier circuit 26. Multiplier 26 multiplies or scales the value 
of the radio altitude signal h.sub.R by a factor of 0.092. The scaled 
value or the radio altitude signal is then applied over line 28 to a 
negative terminal of the summing circuit 22. Summing element 22 
additionally receives at a negative terminal the barometric altitude 
signal h.sub.B by means of line 16. Also applied to a negative summing 
terminal of summing circuit 22 is a biasing quantity equal to 5.4 feet 
delivered over line 30 from the data souce 10. The output of summing 
element 22 is then applied over line 30 to a comparator or logic circuit 
32 which generates a positive output on line 34 if the combination of 
signals on lines 28, 16, 20 and 30 is greater than zero. A positive logic 
output on line 34 indicates that the aircraft has descended a 
predetermined amount below the maximum barometric altitude h.sub.Bmax 
achieved during the take-off or missed approach phase of operation. The 
predetermined amount of altitude loss that will result in a positive value 
on line 34 is dependent on radio altitude such that the greater the radio 
altitude, indicating the altitude of the aircraft above ground, the 
greater the permitted descent below the maximum barometric altitude 
achieved will be before a warning is generated. 
The logic signal on line 34 is then applied to a logic element or AND gate 
36 which in turn is transmitted on a line 38 to a voice warning generator 
40. Examples of similar digital voice warning generators used in ground 
proximity warning systems are provided in U.S. Pat. Nos. 3,925,751, 
4,030,065 and 4,060,793. In the preferred embodiment of the invention the 
voice warning generator 40 will generate the words "don't sink" through a 
cockpit speaker 42 thereby providing the flight crew with the information 
that the aircraft is descending. 
In FIG. 2 of the drawings a graphical representation of the relationship 
between radio altitude and loss of barometric altitude to generate a 
descent warning is provided. The verticle axis represents radio altitude 
in feet and the horizontal axis represents loss of barometric altitude in 
feet with the combinations of radio altitude and barometric altitude loss 
resulting in a negative climb after take-off warning indicated by the 
cross-hatched area 43. As illustrated by the graph of FIG. 2, larger 
descents below the maximum barometric altitude will be permitted for 
greater radio altitude without a descent warning being generated and with 
no warnings being generated below 50 feet of radio altitude. 
As indicated in FIG. 1, since the warning is only generated in the 
preferred embodiment when the aircraft is in a take-off or missed 
approached phase of operation and when the aircraft is descending with 
respect to barometric altitude, logic is provided to ensure that warnings 
are only given under those circumstances. To that end, the data source 10 
provides the signal on line 44 indicating that the aircraft's landing gear 
is in an up position and a signal on line 46 indicating that the 
aircraft's flaps are up. These signals are applied to an OR logic gate 48 
which in turn applies the resulting logic signal to a logic AND gate 52. 
The other input to the logic AND gate 52 is a logic signal on line 54 from 
the data source 10 indicating when the aircraft is 50 feet or more above 
the ground. This signal may be obtained from a radio altimeter. If either 
or both of the landing gear and flaps are up and if the aircraft is above 
50 feet, there will be a logic output from logic gate 52 on line 56 which 
is applied to a logic AND gate 58. Also applied to logic gate 58 is a 
signal over line 60 that indicates that the aircraft is descending with 
respect to barometric altitude. Utilizing a barometric altitude rate 
signal h.sub.B from the data source 10 on line 62 a comparator circuit 64 
will generate a logic signal on line 60 indicating that the aircraft is 
descending with respect to barometric altitude. The third input to logic 
gate 58 on line 66 indicates whether or not the aircraft is in a take-off 
of missed approach phase of operation. 
To indicate that the aircraft is in a take-off or missed approach phase of 
operation the signals on lines 44 and 46 indicating that the landing gear 
and flaps are in an up position are applied to a logic gate 68. Also 
applied to logic gate 68 is a signal on line 70 indicating that the 
aircraft is below a terrain warning curve. The terrain warning curve 
represents another mode of operation of a ground proximity warning system 
that is described in detail in U.S. Pat. Nos. 3,936,796 and 4,030,065. 
When the aircraft is below a terrain warning curve with both the landing 
gear and the flaps up, it is assumed that the aircraft is in a take-off or 
a missed approached phase of operation in which case a logic signal is 
transmitted on line 70 through a delay circuit 72 on line 74 to a latch 
76. A positive logic signal on line 74 will serve to set latch 76 thereby 
transmitting a logic signal on line 66 to logic gate 58. When the aircraft 
exceeds an altitude of 700 feet above ground, thereby indicating that it 
is no longer in a take-off or missed approach phase of operation, a signal 
is transmitted from the data source 10 on line 78 to a logic AND gate 80. 
A logic signal transmitted from gate 80 via line 82 through a delay 
circuit 84 and line 86 has the effect of resetting the latch 76. When 
latch 76 has been reset, the aircraft is no longer in a take-off phase of 
operation and the logic signal on line 66 is turned off. It should be 
noted at this point that an additional validity input is applied over line 
81 to logic gate 68 and 80 to ensure that the signals are valid. 
The logic described in the paragraph above will also serve to indicate when 
the aircraft is in a missed approach phase of operation. Normally when the 
missed approach maneuver is initiated, the aircraft is below the terrain 
warn curve 70 as well as under 700 feet so that when the gear and flaps 
are cycled up, the latch 76 will be set and there will be a logic output 
on line 90. 
As a result when the aircraft is configured with either its gear or flaps 
in an up position, and is 50 feet above the terrain and is in a take-off 
phase of operation while descending with respect to barometric altitude, a 
logic signal will be transmitted from gate 58 on line 90 enabling logic 
gate 36 so that the voice warning can be generated by the voice generator 
40. 
An additional input to logic gate 36 is received over line 92 from a logic 
AND gate 94. A first input to logic gate 94 over line 96 represents a 
logic signal from the data source 10 indicating that the barometric 
altitude rate data is valid. A second logic signal from the data source 10 
is transmitted over line 98 through a delay circuit 100 and line 102 to 
gate 94 and indicates that the barometric altitude data is valid. 
In order to ensure that the barometric altitude data contained in memory 
element 18 represents the aircraft's maximum barometric altitude achieved 
during the take-off phase of operation, a logic signal is transmitted 
through an OR logic gate 106 to the memory element 18. The signal 
transmitted to memory element 18 over line 108 from line 90 indicates that 
the aircraft is in a take-off phase of operation and is descending and 
that the current value of barometric altitude should be retained. The 
value of the barometric altitude in memory element 18 is also retained 
when the value of barometric altitude in the memory element 18 is greater 
than the current barometric altitude, the aircraft is above 50 feet and 
either the gear is up or the flaps are up. This information is obtained 
from a comparator circuit 110 which generates a positive logic signal on 
line 112 when the value of h.sub.Bmax is greater than the aircraft's 
current barometric altitude h.sub.B. This logic signal is then applied to 
a logic AND gate 114. Also applied to logic gate 114 is the logic signal 
from line 56. As a result when the value of the maximum barometric 
altitude exceeds the current barometric altitude, and when the aircraft is 
above 50 feet above the ground with gear or flaps up a logic signal will 
be transmitted on line 116 through logic OR gate 106 to the latch or 
memory element 18 thereby serving to retain the existing value in that 
memory element. 
In the preferred embodiment of the invention it may be considered desirable 
under certain circumstances to give the flight crew additional information 
with respect to the aircraft's configuration as well as the basic negative 
climb after take-off warning which in the preferred embodiment of the 
invention is a "don't sink" voice warning. For example if the landing gear 
is down it would be desirable to give the flight crew an indication that 
the aircraft is sinking and the gear is still down. This is accomplished 
in the preferred embodiment of the invention as illustrated in FIG. 1 by 
means of a logic element 118 that responds to the basic negative climb 
warning on line 38 and the gear up signal on line 44. When the landing 
gear is up the logic signal on line 44 will be transmitted through an 
inverting input of AND gate 18 thus enabling the gate causing a logic 
signal on line 120 to activate a "gear" voice warning on the voice warning 
generator 40. The warning generated through speaker 42 to the flight crew 
will be "don't sink, gear". 
In the event that the aircraft is in a negative climb after take-off with 
the flaps down, a logic AND gate 122 responding to the basic warning 
signal on line 38 and the flaps up signal on line 46 applied through an 
inverting input to AND gate 122 will transmit a logic signal to the voice 
generator over line 124 causing the generation of the warning signal 
"don't sink, flaps". As a result, the flight crew will have more specific 
information as to the aircraft's condition and can be particularly helpful 
in those engine out cases where, due to a very high work load in the 
cockpit, the flight crew may not realize that either the landing gear is 
down or the flaps are down. 
The preferred embodiment of the invention has been described in terms of a 
logic diagram using analog symbols and terminology. However, it should be 
understood that the invention can be implemented in digital circuitry or a 
general purpose digital computer wherein the various symbols contained 
within FIG. 1 would represent logical operations to be performed in the 
digital system. In addition, the various altitudes and descent rates 
described herein are provided in order to illustrate the preferred 
embodiment of the invention and are not intended to limit the scope of the 
disclosure or the invention claimed. Similarly, although the warnings 
described in the preferred embodiment make reference to specific terms 
used in the voice generator such as "don't sink" or "gear" or "flaps", it 
is not intended that the invention as disclosed or claimed be limited to 
those specific terms including the designation of the aircraft 
configuration that is called to the flight crew's attention.