Abstract:
A rate of change in pressure identifies a rapid decompression event in an aircraft, and automatically unlatches a door to allow rapid equalization of pressure throughout the aircraft, allowing for use of doors with greater structural integrity then in current use.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present description generally relates to aircraft, and particularly to securing doors in aircraft. 
     2. Description of the Related Art 
     There is a compelling desire to improve security in aircraft. One area of particular concern is the door in the bulkhead that separates the flightdeck and the passenger cabin of the aircraft. The door must allow access between the flightdeck and the cabin under certain circumstances, for example, when authorized flight crew requires access. The door must prevent access under other circumstances, for example, when unauthorized persons attempt to access the flightdeck. Existing systems include a switch that is controlled from the flight deck and which provides two options (i.e., door locked or latched, door unlocked or unlatched). 
     Existing doors are designed to give way under sudden decompression of either the cabin or the flightdeck, allowing the rapid equalization of the pressure between the flightdeck and the cabin. This is a desirable effect, which may prevent more substantial damage from occurring to the aircraft, caused by the significant variation in pressure between the flightdeck and the cabin during a rapid decompression event. One proposal for improving security includes equipping aircraft with stronger doors and latches in the bulkhead separating the flightdeck and the passenger cabin. However, the additional structural integrity will prevent the doors from giving way during sudden decompression event, preventing the desired rapid equalization of pressure throughout the aircraft. 
     Thus, there is a need for an improved approach in aircraft design that allows for structurally secure doors, while also permitting fast pressure equalization during rapid decompression events. Further, there is a need for an improved approach to controlling access through doors in the bulkheads in aircraft. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect, a system for monitoring interior pressure change in an aircraft having a bulkhead separating a flight deck portion of the aircraft from a cabin portion of the aircraft, the bulkhead including a door and a latch, includes a first pressure sensor that provides flight deck pressure signals corresponding to a rate of change of an ambient pressure in the flight deck portion of the aircraft; and a first comparator responsive to the flight deck pressure signals to provide a first actuation signal in response to a comparison of the rate of change of the ambient pressure in the flight deck portion to at least a first minimum reference level. Determining the rate of pressure change may permit a quicker reaction to a rapid decompression event than would be possible based on a determination of the difference in pressures across a bulkhead. 
     In another aspect, a system for monitoring interior pressure change for an aircraft includes a first pressure sensor responsive to a rate of change of a first ambient pressure in a first portion of the aircraft to produce an output proportional to the rate of change of the first ambient pressure in the first portion of the aircraft; and a comparator responsive to the output of the first pressure sensor to control a door locking mechanism based on a comparison of the rate of change of the first ambient pressure to at least a first reference level. 
     In yet another aspect, a method of monitoring interior pressure change in an aircraft having a bulkhead separating a flight deck portion of the aircraft from a cabin portion of the aircraft, the bulkhead including a door and a latch includes determining a rate of change in an ambient pressure in the fight deck portion of the aircraft, and automatically unlatching the door if the rate of change in the ambient pressure in the flight deck portion of the aircraft exceeds a first minimum threshold. 
     In even a further aspect, a method of monitoring interior pressure change in an aircraft having a bulkhead separating a flight deck portion of the aircraft from a cabin portion of the aircraft, the bulkhead including a door and a latch includes repeatedly determining the ambient pressure in the flight deck portion of the aircraft; and differentiating the determined ambient pressure in the flight deck portion with respect to time. 
     In yet a further aspect, a method of monitoring interior pressure change in an aircraft having a bulkhead separating a flight deck portion of the aircraft from a cabin portion of the aircraft, the bulkhead including a door having a latch determining a rate of change in an ambient pressure in the fight deck portion of the aircraft; automatically unlatching the door if the determined rate of change in the ambient pressure in the flight deck portion of the aircraft is between a first minimum threshold and a first maximum threshold, the first maximum threshold greater than the first minimum threshold. 
     In even another aspect, a method of operating a latch of a door in an aircraft includes determining whether the rate of change in the first interior pressure of the first portion of an aircraft satisfies a defined first set of criteria; and providing an unlatching signal to an actuator to unlatch the door if the rate of change in the first interior pressure in the first portion of the aircraft meets the defined first set of criteria. 
     In still a further aspect, pressure rate sensitive system for use in an aircraft having a flight deck and a cabin separated from the flight deck, includes first rate of change means for determining a rate of change in a pressure in the flight deck; first determination means for determining whether the rate of change in the pressure in the flight deck satisfies a defined first set of criteria; and access controlling means responsive to the first determination means for controlling access between the flight deck and the passenger cabin of the aircraft. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
     In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn, are not intended to convey any information regarding the actual shape of the particular elements, and have solely been selected for ease of recognition in the drawings. 
     FIG. 1 is an isometric view of a portion of an aircraft showing a flight deck, a passenger cabin and various locations for the components of an access control system according to one illustrated embodiment of the invention. 
     FIG. 2 is a block diagram showing an illustrated embodiment of a the access control system including a controller, a number of pressure sensors, a remote request module, and a latch mechanism including a switch and a solenoid. 
     FIG. 3A is a top plan view of the controller. 
     FIG. 3B is a front elevational view of the controller. 
     FIG. 3C is a top, front, right side isometric view of the controller. 
     FIG. 4A is a top plan view of a latch mechanism including a strike for selectively securing a door. 
     FIG. 4B is a left side elevational view of the latch mechanism of FIG.  4 A. 
     FIG. 4C is a rear elevational view of the latch mechanism of FIG.  4 A. 
     FIG. 4D is a rear, top, right side isometric view of the latch mechanism of FIG.  4 A. 
     FIGS. 5A-5B are a functional block diagram showing an illustrated embodiment of the controller. 
     FIG. 6 is a flow diagram of one illustrated method of operating the access control system according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments of the invention. However, one skilled in the art will understand that the invention may be practiced without these details. In other instances, well-known structures associated with aircraft, power systems, doors, latch mechanisms, controllers, and microprocessors have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments of the invention. 
     Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, that is as “including, but not limited to.” 
     The headings provided herein are for convenience only and do not interpret the scope or meaning of the claimed invention. 
     FIG. 1 shows an aircraft  10  having a bulkhead  12  separating a flightdeck  14  from a passenger cabin  16 . The flightdeck  14  is a limited access area, from which authorized personnel, such as pilots, control the aircraft  10 . The passenger cabin  16  is a general access area in which the passengers are seated. A door  18  selectively provides access through an entry in the bulkhead  12  between the flightdeck  14  and passenger cabin  16 . 
     An access control system  20  (FIG. 2) controls the operation of one or more latch mechanisms  21  to latch and unlatch the door  18  for selectively providing access between the flightdeck  14  and the passenger cabin  16 . The terms locked and latched, as well as unlocked and unlatched, are used interchangeably throughout the specification and the claims to refer to a condition in which the door  18  cannot be open and a condition in which the door  18  can be opened, respectively. 
     The access control system  20  includes a controller, generally referenced as  22 , for processing input signals and providing output signals. The controller  22  may be located anywhere in the aircraft  10 , although the flightdeck  14  provides a particularly suitable, secure and conveniently accessible area for the controller  22 . For example, the controller  22   a  may be located on a flight control panel such as a console  26 , within easy reach of the pilots. Alternatively, the controller  22  may be located elsewhere on the flightdeck  14 , for example, the controller  22   b  attached to the bulkhead  12 . 
     The access control system  20  also includes a number of pressure sensors, referenced generally as  24 , for determining ambient pressure levels. At least one of the pressure sensors  24  is located in the flightdeck  14 . For example, one or more pressure sensors  24   a  may be integrated into the controller  22 . Additionally, or alternatively, one or more pressure sensors  24   b  may be mounted separately on the flightdeck  14 , for example, on the bulkhead  12 . 
     Optionally, one or more pressure sensors  24   c  may be located in the passenger cabin  16  for determining the ambient pressure level in the passenger cabin  16 . 
     The access control system  20  may further include an entry request module  28  located in the passenger cabin  16 . For example, the entry request module  28  may be located on the bulkhead  12  next to the door  18  to permit requests for entry to the flightdeck  14  to be made from the passenger cabin  16 . 
     FIG. 2 shows one illustrated embodiment of the access control system  20  including a routing of signals between various elements of the access control system  20 . The controller  22  receives power from a 28V DC supply  30  associated with the aircraft&#39;s power bus, via a circuit breaker  32 . 
     The controller  22  receives signals from the pressure sensors  24   a ,  24   b  on the flightdeck  14 . These signals correspond to the ambient pressure in the flightdeck  14 . The controller  22  may optionally receive signals from one or more pressure sensors  24   c  in the passenger cabin  16 . These signals correspond to the ambient pressure in the passenger cabin  16 . While in some embodiments the ambient pressure signals are proportional to the absolute pressure in the flight deck  14  or passenger cabin  16 , in other embodiments the ambient pressure signals are proportional to the rate of change of pressure in the flight deck  14  or passenger cabin  16 . 
     The controller  22  may receive signals from a switch  34  which is a portion of the latch mechanism  21 . These signals identify the state (e.g., locked/latched or unlocked/unlatched) of latch mechanism  21 . The controller  22  provides signals to a solenoid  36 , also forming part of the latch mechanism  21 , for selectively operating the lock or latch mechanism  21  between the locked/latched and unlocked/unlatched states. 
     The controller  22  may also receive signals from the access entry module  28 , as will be described in further detail below. 
     The controller  22  may provide signals to activate an audio indicator such as a speaker or chime  38 , and/or one or more visual indicators such as lights  40 . The audio and visual indicators can provide a variety of indications regarding the access request system  20 , for example, the status (e.g., operating mode, operating condition) of the access request system  20 , requests for entry, and responses to requests for entry. Audio and/or visual indicators can be located in the flightdeck  14 , as well as the passenger cabin  16 . 
     In an optional embodiment, the controller  22  may further receive input from other aircraft system  42  indicating the status of those systems  42 , where such status has a bearing on the operation of the access control system  20 . For example, the controller  22  may receive input from a weight on wheels sensor that identifies whether there is weight on the wheels of the aircraft  10  indicating that the aircraft  10  is on the ground, or from an external door sensor indicating whether an external door in the aircraft is opened or closed, or from a variety of other aircraft systems  42 . These inputs to the controller may allow the controller  22  to unlock or unlatch the door  18  in the event of a crash landing or in the case of an incapacitated flight crew. 
     FIGS. 3A thru  3 C show the controller  22 . The controller  22  may include connectors  44   a ,  44   b  for making connections to the various components such as the pressure sensors  24 , entry request module  28 , switch  34 , solenoid  36 , speaker or chime  38 , visual indicator  40 , or other aircraft systems  42 . Where the flightdeck pressure sensor  24   a  is mounted in the controller  22 , a face  46  of the controller  22  may include one or more ports  48   a ,  48   b  for providing fluid communication between the pressure sensors  24   a ,  24   b  and the ambient atmosphere of a flightdeck  14 . Multiple ports  48   a ,  48   b , and their associated circuitry (i.e., channels) provide redundancy to the controller  22 . The controller  22  may also include visual indicators such as light emitting diodes (“LEDs”)  50   a ,  50   b ,  50   c  corresponding to respective ones of a top, middle and/or bottom latch mechanism  21  for securing the door  18 . The controller  22  may further include visual indicators such as LEDs  52   a ,  52   b  identifying the status of each channel. 
     FIGS. 4A thru  4 D show one illustrated embodiment of the latch mechanism  21  for securing the door  18  in the bulkhead  12 . As discussed above, the control access system  20  may include one or more latch mechanisms  21 , for example, a top, middle, and bottom latch mechanism  21  for securing the door  18 . 
     The latch mechanism  21  is controlled via the controller  22 . The latch mechanism  21  may include the switch  34  (FIG.  2 ), the solenoid  36  (FIG. 2) and a strike  54 . The latch mechanism  21  may be mounted to the bulkhead  12 , the strike  54  securely engaging and disengaging a portion of the door  18 . Alternatively, the latch mechanism  21  may be mounted to the door  18 , the strike  54  securely engaging and disengaging a portion of the bulkhead  12 . 
     The solenoid  36  may be selectively energized to position the strike  54  for securing the door  18 . In one embodiment, the solenoid  36  is configured such that the solenoid  36  must be energized to place the latch mechanism  21  in the locked state. Thus, the latch mechanism  21  will automatically enter the unlocked state on loss of power to the solenoid  36 , for example in the event of a loss of power in the aircraft  10 . One skilled in the art will recognize that the latch mechanism  21  may employ other equivalent electro-mechanical devices in addition to, or as a substitute for, the solenoid  36 . 
     FIGS. 5A-5B show a particular embodiment of the access control system  20 . The controller  22  receives power via the DC voltage bus  30  of the aircraft  10 . A first 12V power supply  60   a  provides power to the pressure sensors  24   a ,  24   b  and to a first 5V power supply  62   a . A second 12V power supply  60   b  supplies power to a microprocessor  64  via a second 5V power supply  62   b.    
     As discussed above, the pressure sensors  24   a ,  24   b  are in fluid communication with the ambient environment of the flightdeck  14  for detecting the pressure of the ambient environment. The pressure sensors  24   a ,  24   b  provide a signal proportional to the absolute pressure of the ambient environment of the flightdeck  14 . Optionally, pressure sensors  24   c  are in fluid communication with the ambient environment of the passenger cabin  16 , and provide signals proportional the absolute pressure of the ambient environment of the passenger cabin  16 . Some suitable pressure sensors  24  may include a strain gauge on silicon attached to a sealed vacuum reference. Some suitable pressure sensors  24  may have an operating range of 0 to 15 PSIA, with an overpressure rating of 40 PSIA. Some suitable pressure sensors  24  may have an output voltage in the range of 1.5V at 0 PSIA to 9V at 15 PSIA. The control access system  20  may accommodate other values or pressure sensors  24 . 
     Filter and amplifier stages  66   a ,  66   b  filter noise and amplify the signals produced by the pressure sensors  24   a ,  24   b . The filter and amplifier stages  66   a ,  66   b  may reduce environmental control systems transients, acoustical noise, and/or other fast changing signals that would otherwise inadvertently trigger the solenoid  36 . Some suitable filter and amplifier stages  66   a ,  66   b  may, for example, contain a 2-pole unity gain VCVS filter. Some embodiments may omit either the filter, the amplifier, or both. The filtered and amplified signals are provided to differentiators  68   a ,  68   b.    
     The differentiators  68   a ,  68   b  differentiate the filtered and amplified signals to produce signals proportional to a rate of change of pressure (i.e., dP/dt). One skilled in the art will recognize that the controller  22  may employ other suitable circuitry, or even software where processing is rapid enough, for rapidly determining the rate of change of pressure. The rate of change signals are provided to a comparator and monostable vibrator stage  70   a ,  70   b.    
     The controller  22  may optionally include positive pulse suppression circuitry  72   a ,  72   b . The positive pulse suppression circuitry  72   a ,  72   b  suppresses or attenuates signals from the differentiators  68   a ,  68   b  which exceed a defined maximum threshold and/or which are below a defined time duration. The positive pulse suppression prevents false triggering, for example, in response to a sudden change of pressure resulting from the discharge of a firearm or an explosion on board the aircraft  10 . Some suitable positive pulse suppression circuitry  72   a ,  72   b  will attenuate the output from the differentiator  68   a ,  68   b  for approximately 1 ms. 
     The comparator monostable vibrator stages  70   a ,  70   b  determine whether the output from the differentiators  68   a ,  68   b , with or without attenuation, exceeds a defined minimum threshold. The defined minimum threshold corresponds to the rate of change of pressure associated with a rapid decompression event, that requires the unlocking or unlatching of the door  18  to allow rapid equalization of pressure throughout the aircraft  10 . The comparator monostable vibrator stage  70   a ,  70   b  provides signals to an output stage  74 . 
     The output stage  74  is coupled to control the solenoid  36  of the latch mechanism  21 . A suitable output stage  74  may take the form of a MOSFET transistor with a driver that can be driven from either one of two pressure sensing channels, or from an external input. In one embodiment, the external input signals place the solenoid  36  in an ON state when a ground (0V) is present at an appropriate input pin. In this embodiment, the solenoid  36  is in an OFF state when a high impedance is present. The output stage  74  may also include current limiting to protect the MOSFET from excessive currents. 
     The microprocessor  64  is optional in the controller  22  of the control access system  20 . In the typical embodiment, the rate of change sensing circuitry  66 ,  68 ,  70 ,  74 , as well as, the positive pulse suppression circuitry  72 , will take the form of an analog circuit to realize the desired high speed operation of the rate of change sensing functionality. Given the nature of a rapid decompression event, high speed operation is highly desirable. 
     Where included in the control access system  20 , the microprocessor  64  will typically handle user interface functions, such as receiving data  82  from the entry request module  28 , and providing signals  84   a ,  84   b  to selectively actuate visual indicators  86   a ,  86   b  on the entry request module  28 . The microprocessor  64  also provides signals to the visual and/or audio indicators on the controller  22  such as the chime  38  or LEDs  50   a - 50   c . Some suitable microprocessors  64  may include a clock subsystem  76 , power out monitor subsystem  78 , and power on reset subsystem  80 . 
     The controller  22  may also include fault detecting functionality, including fault logic for detecting a fault, a lamp test  84 , and fault LEDs  86  for indicating the existence or absence of a fault. 
     FIG. 6 shows one illustrated method  100  of operating the control access system  20 . In step  102 , the pressure sensors  24  determined the absolute ambient pressure of the flightdeck and/or passenger cabin. As discussed above, suitable pressure sensors may output a signal corresponding to the absolute ambient pressure, or corresponding to a rate of change in ambient pressure. 
     In step  104 , the filter and amplifier stages  66   a ,  66   b  of the controller  22  filters and/or amplifies the signals from the pressure sensors  24 . 
     In step  106 , the differentiators  68   a ,  68   b  of the controller  22  determine the rate of change in pressure from the absolute ambient pressure measurements of the pressure sensors  24 . 
     In step  108 , the positive pulse suppression circuitry  72   a ,  72   b  determines whether the rate of pressure change has exceed a maximum threshold for the rate of change and/or if the change is of too short a duration to correspond to a rapid decompression event. If either the rate of pressure change has exceed a maximum threshold for the rate of change or if the change is of too short a duration, the positive pulse suppression circuitry  72   a ,  72   b  temporarily suppress the signal in step  110 . 
     In step  112 , the comparator monostable vibrator stages  70   a ,  70   b  determine whether the rate of change of pressure exceeds a minimum threshold corresponding to a rapid decompression event. If the rate of change of pressure exceeds the minimum threshold, the comparator monostable vibrator stages  70   a ,  70   b  provides an appropriate signal to the output stage  74 , in step  114 , and the output stage  74  operates the solenoid  36  to unlatch the door  18  in step  116 . The controller  22  then continues to monitor the rate of change in the pressure, returning to step  102 . 
     In step,  118 , the controller  22  determines whether an external unlatch signal has been received. An external unlatch may come from a switch on the controller  22 , or from some other switch in the flightdeck  14 . Typically, such a signal will be generated as a result of the pilot operating a switch to grant access to the flightdeck  14 , perhaps in response to a request generated from the request entry module  28 . If an external unlatch signal has been received, the microprocessor  64  provides an appropriate signal to the output stage  74 , in step  114 , and the output stage  74  operates the solenoid  36  to unlatch the door  18  in step  116 . The controller  22  then continues to monitor the rate of change in the pressure, returning to step  102 . 
     While not illustrated, the microprocessor  64  may provide for a number of modes. For example, in one mode, the microprocessor  64  may provide the pilot with a defined period of time in which to deny a request for entry, providing the unlatch signal to the output stage  74  if the pilot fails to activate an appropriate switch within the defined time. In this mode, the pilot may 1) unlock the door immediately by activating a first switch; 2) deny entry by activating a second switch; 3) deny entry and enter a ‘secure’ mode described above; or 4) permit entry by taking no action. In the ‘secure’ mode, the microprocessor  64  may lock out all requests for access generated by the entry request module  28 . This allows the pilots to fly the aircraft  10  without interruption. 
     Similar subject matter is described in commonly assigned U.S. Provisional Applications Serial Nos. 60/349,774, filed Jan. 16, 2002, entitled “PRESSURE SENSITIVE LATCHING METHOD AND APPARATUS” (Atty. Docket No. 700118.401P1); and No. 60/415,441, filed Oct. 1, 2002, and entitled “PRESSURE SENSITIVE LATCHING METHOD AND APPARATUS” (Atty. Docket No. 700118.401P2). Much of the detailed description provided herein is disclosed in the provisional application, and most additional material, if any, will be recognized by those skilled in the relevant art as being inherent in the detailed description provided in such provisional patent application or well-known to those skilled in the relevant art based on the detailed description provided in the provisional patent application. Those skilled in the relevant art can readily create source code based on the detailed description provided herein. 
     Although specific embodiments of, and examples for, a secured access system are described herein for illustrative purposes, various equivalent modifications can be made without departing from the spirit and scope of the invention, as will be recognized by those skilled in the relevant art. For example, the secure access system may be employed for controlling access and providing for rapid pressure equalization to other areas of the aircraft, not necessarily between the flightdeck and the passenger cabin. In some embodiments, the functionality can be moved from one subsystem to another. For example, as will be recognized by one skilled in the art, the determination of the rate of change in pressure can be moved from the controller  22  to the sensor modules  24 . The teachings provided herein can be readily applied to other secure access systems, not necessarily the exemplary flightdeck secure access system generally described above. 
     The various embodiments as described above can be combined to provide further embodiments. All of the above U.S. patents, patent applications, and publications referred to in the specification are incorporated herein by reference, in their entirety. Aspects of the invention can be modified, if necessary, to employ systems, circuits, and concepts of the various patents, applications, and publications to provide yet further embodiments of the invention. 
     These and other changes can be made to the invention in light of the above detailed description. In general, in the following claims, the terms used should not be construed to limit the invention to the specific embodiments disclosed in the specification and claims, but should be construed to include all secured access systems that operate in accordance with the claims. Accordingly, the invention is not limited to the disclosure, but instead its scope is to be determined entirely by the following claims.