Adaptive aircraft cabin pressure control system

An adaptive aircraft cabin pressure control system is disclosed that customizes basic ascent and descent schedules to accommodate variable requirements of specific airlines, the airlines' route structures, and regional air traffic control standards. The system includes an adaptive control logic that identifies a plurality of points generated by the schedules that define ascent and descent curves corresponding to anticipated cabin pressure change rates during ascent and descent. During aircraft flight, the logic samples and stores actual cabin pressure change rates at each of the plurality of points. After the flight, the actual cabin pressure change rates are averaged and the average rate is compared to the anticipated cabin pressure change rate at each point. An offset is then calculated representing the difference between the average actual rate and an anticipated rate, and the ascent and/or descent schedules are adapted by the offset to bring the anticipated cabin pressure change rates closer to the average actual rate. After several flights, the ascent and descent schedules are customized by the adaptive control logic to a particular airline's requirements.

BACKGROUND OF THE INVENTION 
The present invention relates to an aircraft cabin pressure control system 
for controlling aircraft cabin pressure during aircraft ascent, cruise and 
descent. In particular, a system is disclosed for adapting control of 
rates of cabin pressure changes to meet variable requirements of 
particular airlines, the airlines' specific route structures, and regional 
air traffic control standards. 
Air pressure within an aircraft cabin is controlled during an entire flight 
profile to minimize passenger discomfort, and ensure a maximum pressure 
differential between the cabin and ambient pressures is not exceeded. In a 
typical flight from a coastal or sea-level city to a landing site slightly 
above sea level, at takeoff, pressure within the aircraft cabin (P.sub.c) 
and actual ambient pressure (P.sub.a) outside of the cabin are 
approximately the same, 14.70 pounds per square inch ("p.s.i."). The 
aircraft takes off and ascends to an altitude of 45,000 feet, for example, 
where P.sub.a decreases to approximately 2.14 p.s.i. Then, the aircraft 
cruises for a specific time at that altitude, until it descends to the 
landing site, which has an ambient pressure (P.sub.ld) slightly lower than 
the P.sub.a at take off. During such a flight, the cabin pressure 
decreases during the ascent so that a minimum human comfort pressure of 
approximately 10.92 p.s.i. (equivalent to an altitude of approximately 
8,000 feet) is not exceeded, and the maximum differential between P.sub.a 
and P.sub.c is not exceeded, as well. During descent, P.sub.c increases so 
that it is approximately the same as the P.sub.ld slightly before the 
aircraft lands. That ensures P.sub.c is at a slightly higher pressure than 
P.sub.a when the aircraft lands, thereby allowing the aircraft doors to be 
opened easier in an emergency. Maximum passenger comfort during the flight 
is achieved by minimizing the rate of cabin pressure change during ascent 
and descent, so that the rates do not exceed the equivalent of 
approximately 500 feet per minute ("f.p.m.") for ascent and 300 f.p.m. for 
descent. 
Known systems for controlling aircraft cabin pressure utilize a cockpit 
selector panel to communicate with an electronic cabin pressure 
controller, which actuates an outflow valve. The cabin is pressurized by 
compressed bleed air directed into the cabin from the aircraft's engines. 
Modulation by the controller of the outflow valve controls rate of air 
flow out of the cabin, thereby controlling cabin pressure. 
As described in U.S. Pat. No. 3,473,460 to Emmons, incorporated herein by 
reference, and assigned to the assignee of the present invention, an 
automated system for controlling the rate of aircraft cabin pressure 
change is disclosed that utilizes the aforesaid three parameters, P.sub.a, 
P.sub.c and P.sub.ld, in a function generator (FIG. 1, No. 33) having a 
single, non-adjustable operating line as a function of the difference 
between P.sub.a and P.sub.ld to provide a set point for the desired rate 
of cabin pressure change. Such a non-adjustable operating line constrains 
control of cabin pressure rate changes to only values along the 
non-adjustable operating line of the function generator. Therefore, that 
system could not anticipate a literally infinite number of possible cabin 
pressure ascent and descent profiles resulting from geography, weather, 
air traffic control, etc. 
An improved system for controlling the rates of aircraft cabin pressure 
change is disclosed in U.S. Pat. No. 5,186,681, filed on Sep. 30, 1991, 
incorporated herein by reference, and assigned to the assignee of the 
present invention. It discloses a method for generating a variable desired 
rate of cabin pressure change that utilizes schedules stored in the 
controller that incorporate specific rate limit set points, or that 
include non-linear functions correlating cabin pressure to ambient 
pressure or ambient pressure rates of change. The schedules are typically 
supplied by aircraft manufacturers, and attempt to typify a range of 
aircraft flight profiles. 
Such schedules, however, have been unable to accommodate varying demands of 
a world-wide airline market. Typically, North American, European and Asian 
airlines utilize significantly different flight profiles. For example, an 
European airline having numerous flights between France and Italy would 
utilize much more rapid ascents and descents than an airline flying 
primarily up and down the East Coast of North America. Additionally, Asian 
operators frequently have unique cruise schedules, which impact rates of 
ascent and descent. Finally, regional air traffic control requirements 
(e.g., duration and frequency of holding patterns) likewise impact unique 
characteristics to an airline's typical flight profiles, rendering fixed, 
rate-limit or non-linear control schedules in need of custom adaptation 
for specific usage. 
Accordingly, it is the general object of the present invention to provide 
an adaptive aircraft cabin pressure control system that overcomes the 
deficiencies of the prior art. 
It is a more specific object to provide an adaptive aircraft cabin pressure 
control system that accommodates specific requirements of all airlines. 
It is another specific object to provide an adaptive aircraft cabin 
pressure control system that can be implemented in existing aircraft cabin 
pressure control systems. 
It is yet another object to provide an adaptive aircraft cabin pressure 
control system that automatically adapts existing schedules for 
controlling aircraft cabin pressure to requirements of a specific flight 
profile. 
The above and other objects and advantages of this invention will become 
more readily apparent when the following description is read in 
conjunction with the accompanying drawings. 
SUMMARY OF THE INVENTION 
An adaptive aircraft cabin pressure control system is disclosed for 
controlling aircraft cabin pressure during an entire flight profile 
including ascent, cruise and descent. The control system is utilized to 
minimize passenger discomfort, and to ensure a maximum pressure 
differential between the cabin and ambient pressure is not exceeded. 
In the preferred embodiment, the invention comprises a selector panel in 
the cockpit of the aircraft that enables the aircraft operator to input 
specific planned flight data and to select commands for controlling cabin 
pressure; an electronic cabin pressure controller that receives the flight 
data and executes the commands from the selector panel, thereby producing 
cabin pressure control signals; an outflow valve that receives the signals 
from the controller and, in response to the signals, modulates flow of 
pressurized air out of the aircraft cabin, thereby controlling cabin 
pressure; ascent and descent schedules stored in the controller for 
maintaining the desired cabin pressure rates based upon receipt of signals 
from the aircraft's sensors and avionics identifying cabin pressure 
(P.sub.c), external ambient pressure (P.sub.a), ambient pressure at cruise 
altitude (P.sub.cr), cabin pressure at cruise altitude (P.sub.cc), and 
ambient pressure at a landing sight (P.sub.ld); and an adaptive control 
logic stored in the controller that samples actual cabin pressure rates 
during a flight and adapts the schedules based upon variations between the 
actual rates and the rates anticipated by the schedules. 
In use, prior to a flight, the schedules are loaded into memory components 
of the controller. The selector panel transmits signals identifying the 
P.sub.cr, P.sub.cc and P.sub.ld to the controller as part of the planned 
flight data. Additionally, the controller monitors the P.sub.c and P.sub.a 
via signals from the aircraft's sensors. The schedules include logic 
executed by a microprocessor in the controller, in response to the 
signals, to control rates of change of the cabin pressure. 
During the ascent and descent, the adaptive control logic samples and 
stores actual cabin rates of change at a plurality of intervals 
corresponding to specific points in the ascent and descent schedules. 
After the flight, the stored rates are averaged and compared to rates 
anticipated by the schedules. The schedules are then automatically 
adjusted by slightly moving the points in the schedules in response to the 
adaptive control. Consequently, after several flights, the schedules 
become adapted to specific aircraft operating conditions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings in detail, the preferred embodiment of an 
adaptive aircraft cabin pressure control system of the present invention 
is shown and generally designated by the numeral 10. The invention 
basically comprises a selector panel 12 within a cockpit 14 of an aircraft 
16 that enables an operator (not shown) to transmit planned flight data 
and to select commands for controlling air pressure within the aircraft's 
cabin 18; an electronic cabin pressure controller 20 (hereinafter 
"controller") within the aircraft 16 that receives signals from the 
aircraft's sensors and avionics 22 and commands from the selector panel 12 
and produces output command signals; a variable flow outflow valve 24 that 
receives the output command signals from the controller 20 and modulates 
flow of pressurized cabin air out of the cabin 18 in response to the 
signals, thereby controlling cabin pressure; ascent and descent schedules 
26 and 28 stored in the controller 20 for maintaining desired cabin 
pressure change rates; and an adaptive control means or logic stored in 
the controller 20 that samples and stores actual cabin pressure rates 
during a flight and adapts the schedules 26, 28 based upon variations 
between the actual rates and rates anticipated by the schedules. 
As best shown schematically in FIG. 1, compressed bleed air is directed 
from the aircraft's engines 32a, 32b through air conditioners 34a, 34b and 
into the cabin 18, to pressurize the cabin air, as is generally known in 
the art. The pressurized air exits the cabin 18 through the variable flow 
outflow valve 24 at a rate determined by the controller 20, thereby 
controlling air pressure within the cabin 18. 
As seen in FIG. 2, the controller 20 includes a microprocessor 36 (such as 
INTEL.RTM., Model No. 80486, manufactured by Intel Corporation, of Santa 
Clara, Calif., or MOTOROLA.RTM., Model No. 68020, manufactured by 
Motorola, Inc., of Schaumberg, Ill.); a standard memory 38 (including 
known elements such as RAM, PROM and EEPROM components); input/output 
ports 40, 42, which include standard analog-to-digital and 
digital-to-analog convertors; and, a standard address/data bus 44. The 
output command signals generated by the controller 20 travel on line 46 to 
the outflow valve 24. An example of such a valve is disclosed in U.S. Pat. 
No. 3,740,006 to Maher, and assigned to the assignee of the present 
invention. 
As also shown in FIG. 2, a plurality of variables are sent to the 
controller 20, in the form of signals, from standard known aircraft 
avionics and sensors 22. Throughout this disclosure, the variables will be 
continuously identified. To facilitate disclosure, the variables are 
listed and identified below in the following chart: 
______________________________________ 
VARIABLE EXPLANATION 
______________________________________ 
P.sub.a* External aircraft ambient pressure 
P.sub.c* Cabin pressure 
P.sub.cr* Ambient pressure at cruise altitude 
P.sub.cc* Cabin pressure at cruise altitude 
P.sub.cd* Desired cabin pressure 
P.sub.ld* Ambient pressure at aircraft landing site 
K.sub.1 Initial rate of descent 
K.sub.2 Desired ratio of DP.sub.c /DP.sub.a as a function of a 
typical DP.sub.a followed during a descent. 
(For purposes of this disclosure, "D" means 
"Delta".) 
P.sub.cs Schedule output specific to aerodynamic 
climb characteristics of an aircraft 
K.sub.ma Ascent multiplier equivalent to (P.sub.c - P.sub.cc)*P.sub.cs 
K.sub.md Descent multiplier equivalent to 
(DP.sub.c /DP.sub.a)/K.sub.2 
P.sub.ci Climb pressure schedule 
C.sub.1 Gain factor 
______________________________________ 
*It is stressed that only the asterisked variables (P.sub.a, P.sub.c, 
P.sub.cr, P.sub.cd and P.sub.ld) share common explanation or meaning with 
similar or identical variables in U.S. Pat. No. 5,186,681, previously 
incorporated herein by reference, and assigned to the assignee of the 
present invention. The remaining, nonasterisked variables are limited to 
the specific explanation or meaning recited herein, and do not share 
common meanings with variables in that application. 
As seen in FIG. 2, the aircraft avionics and sensors 22 send to the 
controller signals identifying ambient pressure at cruise altitude 
(P.sub.cr) on a line 50; ambient pressure at the aircraft landing site 
(P.sub.ld) on a line 52; cabin pressure at cruise altitude (P.sub.cc) on a 
line 54; sensed ambient pressure (P.sub.a) on a line 56; sensed cabin 
pressure (P.sub.c) on a line 58; and a signal on line 60 indicating 
whether the aircraft's ascent or descent is complete. These six signals 
may be provided over the aircraft's digital bus (e.g., ARINC 429 or 629) 
(not shown), if so equipped, or by dedicated electrical lines presented to 
the controller, or in any other appropriate manner. 
Ascent schedule 26 stored in a PROM 62 component of the controller's memory 
38 has an ascent logic 64 schematically represented in FIG. 3. In a first 
step 66, a schedule output P.sub.cs specific to aerodynamic 
characteristics on the aircraft 16 is entered, while the controller reads 
signals from the aircraft's avionics and sensors identifying ambient 
pressure at selected cruise altitude P.sub.cr, actual ambient pressure 
P.sub.a, cabin pressure P.sub.c, and ambient pressure at a landing site 
P.sub.ld. In a second step 68, an ascent multiplier K.sub.ma is calculated 
by the following quotation: 
EQU K.sub.ma =(P.sub.c -P.sub.cc)*P.sub.cs (Eq. 1) 
In the third step 70, a climb pressure schedule (P.sub.ci) is determined by 
the following quotation: 
EQU P.sub.ci =P.sub.cc +(K.sub.ma *P.sub.cs) (Eq. 2) 
The resulting climb pressure schedule P.sub.ci is executed by the 
controller's microprocessor 36 during ascent of the aircraft 16 to control 
the outflow valve 24, thereby controlling cabin pressure change rate. As 
seen in FIG. 7, the resulting climb pressure schedule P.sub.ci, as 
determined above, or as determined by alternative known methods, exhibits 
a variable cabin pressure rate ascent curve 72, having a shape generally 
designed by ascent graph 74. 
By the present invention, a fourth step 76 of the ascent logic 64 
identifies a plurality of ascent points 78a-h (see FIG. 7), which define 
the ascent curve 72. The adaptive control means 30 utilizes an adaptive 
ascent means or logic 80, stored in an EEPROM memory component 81 of the 
controller memory 38, and shown schematically in FIG. 3. In a first ascent 
step 82, the adaptive logic 80 reads and stores rates of change in actual 
cabin pressure (DP.sub.c) at ascent points 78a-h, shown on ascent graph 
74. In a second ascent step 84, after the aircraft's ascent is completed, 
the logic averages the stored rates, and then in a third ascent step 86, 
compares the average to the rate of cabin pressure change anticipated by 
the ascent schedule 26 at each point 78a-h. In a fourth ascent step 88, 
the logic determines if the average rate differs from the anticipated rate 
at each point 78a-h by more than some predetermined amount, for example, 
25 feet per minute. If so, the logic calculates a specific offset to 
adjust the associated point. The offset is then communicated by line 90 to 
the third step 70 of the ascent logic 34 to adjust the climb pressure 
schedule (P.sub.ci) to make the offset to the associated point in the 
climb pressure schedule. 
The fourth ascent step 88 of the adaptive logic 80 limits calculation of 
offset valves to exclude variations beyond a preset range, so that 
abnormal aircraft ascents (e.g., maneuvering to avoid a storm) would not 
generate offsets. The effect of the adaptive control logic 30 after 
several flights is to "ratchet" the basic climb pressure schedule 
(P.sub.ci) into a custom schedule that encompasses peculiarities of an 
airline's unique flight characteristics. 
It is possible to use the above-described application of the ascent 
schedule 26 to control rate of cabin pressure (P.sub.c) change during the 
descent phase of an aircraft's flight profile. However, an aircraft 
descent phase differs significantly from ascent because of a high 
probability of an aircraft being placed in a holding pattern by air 
traffic control, prior to landing. Standard practice therefore has been to 
implement a constant rate of cabin pressure change through the duration of 
the entire descent, including any such holding patterns, to maximize 
efficiency of aircraft descents by minimizing the rate of cabin pressure 
change. Consequently, optimal descent rates of cabin pressure change are 
utilized that hinge upon an initial rate of descent K.sub.1. A desired 
rate of cabin pressure change is determined by the following equation: 
EQU RATE=K.sub.1 +C.sub.1 *(DP.sub.c /(DP.sub.a -K.sub.2)) (Eq. 3) 
where: 
K.sub.1 =Initial rate of descent; 
C.sub.1 =Gain factor; 
DP.sub.c =Pressure at the landing site (P.sub.ld)--Cabin pressure at the 
start of descent (P.sub.c); 
DP.sub.a =Pressure at the landing site (P.sub.ld)--Ambient pressure at the 
start of descent (P.sub.a); and 
K.sub.2 =The typical ratio of DP.sub.c /DP.sub.a as a function of DP.sub.a 
that would be followed during the descent. 
The descent schedule 28, stored in the PROM 62 component of the 
controller's memory 38, has a descent logic 92 schematically represented 
in FIG. 4. In known descent schedules, the aforesaid K.sub.2 ratio of 
DP.sub.c /DP.sub.a is stored as an equation that exhibits a variable cabin 
pressure rate descent curve 93 shown in the descent graph 94 of FIG. 8. By 
the present invention, K.sub.2 is stored as a plurality of descent points 
in a first step 96 of the descent logic 92, such as the descent points 
95a-h indicated in FIG. 8, which points define a descent curve 93. At the 
start of the descent in a second step 98 of the descent logic 92, the 
constants are initialized through signals identifying the cabin pressure 
(P.sub.c), external ambient pressure (P.sub.a), and the ambient pressure 
at the landing site (P.sub.ld), and through determination of the descent 
multiplier K.sub.md, by the following quotation: 
EQU K.sub.md =(DP.sub.c /DP.sub.a)/K.sub.2 (Eq. 4) 
In a third step 100 of the descent logic 92, K.sub.2 of the basic descent 
rate equation (Eq. 3) is multiplied by K.sub.md at the start of the 
descent to set the second part of the equation to zero, by setting K.sub.2 
at the actual (DP.sub.c /DP.sub.a), instead of its ordinary valve as the 
desired (DP.sub.c /DP.sub.a). The resulting rate is executed by the 
microprocessor 36 of the controller 20 during descent of the aircraft 16 
to control outflow valve 24, thereby controlling cabin pressure change 
rate. 
By the present invention, adaptive control logic 30 operates to adapt the 
descent schedule 28 in much the same manner as with the ascent logic 64. 
Adaptive control 30 utilizes an adaptive descent means or logic 102 stored 
in the EEPROM memory component 81 of the controller memory 38 and shown 
schematically in FIG. 4. For a first descent step 104 of the logic 102, 
rates of change in actual cabin pressure (DP.sub.c) at descent points 
95a-h are read and stored. In a second descent step 106, after the 
aircraft's descent is completed, the logic averages the stored rates, and 
then, in a third descent step 108, the logic compares the average to the 
rate of cabin pressure change anticipated by the descent schedule 28 at 
each point 95a-h. In a fourth descent step 110, the logic determines if 
the average rate is higher than the anticipated rates, or K.sub.1. If so, 
the fourth step 110 determines an offset amount to move K.sub.1 so it is 
closer to the average of the actual rate. Alternatively, if the average of 
the actual rate is different than K.sub. 1, the fourth step 110 can 
calculate an offset to adjust K.sub.2 closer to the actual rate. The 
offset is then communicated by line 112 to the second step 98 of the 
descent logic 92 to adjust K.sub.1 or K.sub.2. 
As with the adaptive ascent logic 80, fourth descent step 110 of the 
adaptive descent logic 102 limits calculation of offset values to exclude 
variations beyond a preset range, so that abnormal aircraft descents 
(e.g., extremely long holding patterns, diversions away from storms) would 
not generate offsets. The result is a descent rate control which adapts 
itself to actual descent profiles being flown by a particular airline. 
It should be understood by those skilled in the art that obvious 
modifications in the above disclosure can be made without departing from 
the spirit of the invention. For example, ascent and descent logic 64, 92 
of the ascent and descent schedules 26, 28 may determine optimal rates of 
cabin pressure (P.sub.c) change in a variety of known methods. 
Additionally, the ascent and descent logic 64, 92, as well as the adaptive 
ascent and descent logic 80, 102, may be stored in a variety of memory 
devices known in the art. Also, the adaptive control logic 30 is 
susceptible of a variety of similar corrective, adaptive applications to 
adapt variable output functions. Accordingly, reference should be made 
primarily to the accompanying claims, rather than the foregoing 
Specification, to determine the scope of the invention.