Abstract:
A warning indication system and method of using the same in conjunction with a cargo door of an aircraft. The cargo door is positionable in an opened position; a closed position; a closed and latched position; and a closed, latched, and locked position. The method includes outputting first and second closed signals when the cargo door is in the closed position; outputting first and second latched signals when the cargo door is in the closed and latched position; and outputting first and second locked signals when the cargo door is in the closed, latched, and locked position. All of the signals are then analyzed to positively determine the position of the cargo door, while minimizing the probability of false indications. Various warnings are generated in response to the combination of signals received. The apparatus employs a dual logic system and redundant sensors to provide differing warnings dependent on the phase of flight.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to aircraft cargo doors and, more particularly, relates to an electrical control and warning indication system for use with an aircraft cargo door that employs and a method of using the same.  
         BACKGROUND OF THE INVENTION  
         [0002]    According to the Federal Aviation Administration (FAA), the certification requirements of warning systems on outwardly opening cargo doors state that erroneous closed, latched, and locked indication (i.e., the loss of indication) must be shown to be “improbable”, which generally means having a probability of occurrence of less than or equal to 1 per 100,000 flights. Although the current text of the rules do not explicitly require it, it has recently been required by regulatory agencies that the manufacturer of airplanes with outwardly opening cargo doors demonstrate that nuisance indication is also “improbable.” In addition, regulatory agencies have expended significant effort to reduce occurrences of unnecessary rejected takeoffs resulting from nuisance warning indications.  
           [0003]    It has been possible to meet, although marginally, the improbable erroneous indication requirements with existing single channel indication systems. However, it has not always been possible to meet the requirements that nuisance indication also be improbable. In the instances where it was not possible to comply fully with the nuisance indication requirement, the regulatory agencies involved have noted the difficulty in meeting this requirement and have accepted this limitation.  
           [0004]    With reference to single channel systems, it is not generally possible to determine if a warning is accurate, or not, nor has it been possible to reduce the probability of both erroneous and nuisance indication. Because of these limitations, significant reductions in the occurrence of rejected takeoffs due to false cargo door indications have not been realized.  
           [0005]    The indication systems on outwardly opening, cargo doors having cam-type latches have historically been single channel systems. Because of this, these single channel systems have not been able to determine if the closed, latched, or locked status of the cargo door is erroneous or not. Therefore, if either of the closed, latched, or locked state of the cargo door should transition to the inverse state, a warning message must be provided. If this indication is erroneous, and occurs during the takeoff roll, a risky heavy weight rejected takeoff must be performed.  
           [0006]    Closed, latched, and locked status indications of a cargo door is often provided at a cargo door operator&#39;s control panel near the cargo door opening. An example of such an indication system is provided in U.S. Pat. No. 5,735,487, commonly owned herewith, the disclosure of which is incorporated herein by reference. However, known control panels have not incorporated features to deactivate the warnings if faults are detected prior to flight and the airplane is being dispatched per Minimum Equipment List conditions with the warning system working improperly.  
           [0007]    Accordingly, there exists a need in the relevant art to provide visual and aural warning indications relative to the safety status of an outwardly opening cargo door on transport category airplanes. Moreover, there exists a need in the relevant art to provide a warning indication system that is capable of distinguishing whether a warning indication is false, thereby reducing the occurrence of unnecessary rejected takeoffs. Furthermore, there exists a need in the relevant art to provide a warning indication system that overcomes the disadvantages of the prior art systems.  
         SUMMARY OF THE INVENTION  
         [0008]    According to the principles of the present invention, a cargo door electrical control and warning indication system having an advantageous construction and method of use is provided. The warning indication system is adapted for use with a cargo door of an aircraft. The cargo door being positionable in an opened position; a closed position; a closed and latched position; and a closed, latched, and locked position. The method includes outputting first and second closed signals when the cargo door is in the closed position; outputting first and second latched signals when the cargo door is in the closed and latched position; and outputting first and second locked signals when the cargo door is in the closed, latched, and locked position. All of the signals are then analyzed to positively determine the position of the cargo door, while minimizing the probability of false indications. Various warnings are generated in response to the combination of signals received. The apparatus employs a dual logic system and redundant sensors to provide differing warnings dependent on the phase of flight.  
           [0009]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0011]    [0011]FIG. 1 is a perspective view of an airliner incorporating a cargo door electrical control and warning indication system according to the principles of the present invention;  
         [0012]    [0012]FIG. 2 is a fluid circuit diagram illustrating the warning indication system of the present invention;  
         [0013]    [0013]FIG. 3 is an electrical control circuit diagram illustrating the cargo door electrical control and warning indication system according to the principles of the present invention;  
         [0014]    [0014]FIG. 4 is an electrical warning indication circuit diagram illustrating the cargo door electrical control and warning indication system according to the principles of the present invention;  
         [0015]    [0015]FIG. 5 is a warning indication logic diagram illustrating the cargo door electrical control and warning indication system according to the principles of the present invention;  
         [0016]    [0016]FIG. 6 is a front view of a door operator&#39;s control panel according to the present invention;  
         [0017]    [0017]FIG. 7 a  is a front view of a flight deck forward overhead warning panel according to the present invention;  
         [0018]    [0018]FIG. 7 b  is a front view of a flight deck glareshield warning panel according to the present invention:  
         [0019]    [0019]FIG. 7 c  is a front view of a flight deck aft overhead warning panel according to the present invention; and  
         [0020]    [0020]FIG. 8 is a warning indication logic table illustrating the warning indication according to various timing conditions. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For example, cargo door  10  warning indication system of the present invention may find utility in a wide range of applications, such as in use with a cargo aircraft, a convertible aircraft, and the like. Although the following description is directed to the warning system as it is used in a conventional, convertible, large-capacity, commercial airliner, the warning system should not be construed to be limited to such applications.  
         [0022]    Referring to the figures, a cargo door  10  is an electrically controlled, hydraulically actuated, outwardly opening, non-plug cargo door. Cargo door  10  opens to two positions in order to provide a clear opening for loading and unloading of containerized and/or palletized cargo into and out of a main deck compartment of an aircraft  14 . Indication of the closed, latched, and locked status of cargo door  10  is provided at both an door operator control panel  16  and on a flight deck  18 . Appropriate colors, in combination with text on the warning and status lights, are used to warn cargo door  10  operator and the flight crew when cargo door  10  is in an unsafe configuration.  
       Electrical Control System  
       [0023]    With particular reference to FIGS. 2, 3, and  6 , an electrical control and indication system  20  provides the power required for normal operation of a hydraulic latch mechanism  22 , hydraulic pull-in mechanisms  24 , and a hydraulic lift mechanism  26 . Control and indication system  20  consists of a circuit breaker  28 , an UP TO CANOPY switch  30 , a FULL OPEN switch  32 , a first canopy switch  34 , a second canopy switch  36 , a door closed A switch  38 , a door unlocked switch  40 , an air/ground relay  42 , and two electrically controlled hydraulic valves, specifically a motor operated selector valve  44  and a solenoid operated isolation valve  46 . To electrically command cargo door  10  to open or close, the following conditions must be met: 1) aircraft  14  must be on the ground; 2) the landing gear selector lever must be positioned in the DOWN position (see valve  62  in FIG. 2); 3) the hydraulic system must be operating; 4) there must be  28 V DC available from circuit breaker  28 ; and 5) a lock and vent panel mechanism (not shown) must be in the unlocked position, which causes door unlocked switch  40  to be in the UNLOCKED position.  
         [0024]    As best seen in FIG. 6, UP TO CANOPY switch  30  and FULL OPEN switch  32  are located on door operator control panel  16 . Door operator control panel  16  is located just inside cargo door  10 . UP TO CANOPY switch  30  and FULL OPEN switch  32  are momentary make, three-position, spring loaded, center-off, toggle switches. UP TO CANOPY switch  30  controls cargo door  10  operation up to a canopy position and back to a closed position. FULL OPEN switch  32  controls cargo door  10  operation from the canopy position up to a fully opened position and back to canopy position. UP TO CANOPY switch  30  and FULL OPEN switch  32  are operated in sequence to raise cargo door  10  to full open and to close cargo door  10 . If UP TO CANOPY switch  30  and FULL OPEN switch  32  are operated out of sequence or simultaneously, cargo door  10  will not operate. When cargo door  10  is locked, both UP TO CANOPY switch  30  and FULL OPEN switch  32  are electrically disabled by door unlocked switch  40 .  
         [0025]    Air/ground relay  42  provides the electrical ground to enable operation of solenoid operated isolation valve  46  when aircraft  14  is on the ground. The electrical ground for control and indication system  20  is removed if the air/ground relay  42  is in the air mode (airplane in-flight and air/ground relay  42  is thus opened).  
         [0026]    Motor operated selector valve  44  is preferably located in the right hand aft wing to body fairing compartment. Motor operated selector valve  44  is a motor driven, two-position, sequence valve with four ports and a manual override lever. Motor operated selector valve  44  has two internal double pole switches  50 ,  52 . The two positions of motor operated selector valve  44  are identified as POS  1  (door open) and POS  2  (door close) and are marked adjacent to a manual override lever. Position switches  50 ,  52  alternately complete power circuits to each side of a split winding in a motor  54 , thereby allowing motor  54  to drive selector valve  44  to POS  1  or POS  2 . When selector valve  44  moves to one extreme position, the switch (either  50 ,  52 ) connected to the driven winding is opened, thus automatically stopping motor  54 , and the switch (either  52 ,  50 ) connected to the opposite winding is closed when selector valve  44  leaves the opposite extreme position. Motor  54  operates on 28V DC and is protected by circuit breaker  28 .  
         [0027]    Solenoid operated isolation valve  46  is in the same general aircraft location as motor operated selector valve  44 . Isolation valve  46  is a solenoid driven, piston-type, two-position isolation valve with three ports-a pressure port  56 , an output port  58 , and a return port  60 . Pressure port  56  is connected to the hydraulic pressure lines downstream of a landing gear selector bypass valve  62 . When a solenoid  64  of isolation valve  46  is energized, solenoid  64  moves the piston of isolation valve  46  to connect pressure port  56  to output port  58  and return port  60  is blocked. This position ports hydraulic pressure to motor operated selector valve  44 . When solenoid  64  is de-energized, the piston of isolation valve  46  connects output port  58  to return port  60  and pressure port  56  is blocked. This position, wherein pressure port  56  blocked, is the normal deenergized state of isolation valve  46 . Solenoid  64  operates on  28 V DC and is protected by circuit breaker  28 .  
         [0028]    When cargo door  10  is closed, door closed A switch  38  prevents uncommanded opening by electrically isolating cargo door  10  open (POS  1 ) coil  50  of motor operated selector valve  44 . First canopy switch  34  and second canopy switch  36  are actuated in response to lift mechanism  26 . During opening of cargo door  10  to the canopy and full open positions, second canopy switch  36  provides power to POS  1  of motor operated selector valve  44  when either UP TO CANOPY switch  30  or FULL OPEN switch  32  are respectively selected to the UP TO CANOPY and FULL OPEN positions. During opening to the canopy position, as motor operated selector valve  44  transitions from POS  2  to POS  1 , power is removed from the windings of motor operated selector valve  44  and applied to solenoid operated isolation valve  46  via the internal POS  1  switch and UP TO CANOPY switch  30 . At approximately  870  of door open rotation, lift mechanism  26  actuates second canopy switch  36 , which removes power from solenoid operated isolation valve  46 , thereby stopping motion of cargo door  10 . To continue opening cargo door  10  from the canopy position (approximately 87° open) to the fully open vertical position, FULL OPEN switch  32  is placed in the FULL OPEN position. Power to solenoid operated isolation valve  46  is provided by FULL OPEN switch  32 , via second canopy switch  36  and internal POS  1  switch  50  of motor operated selector valve  44 .  
         [0029]    To close cargo door  10  from the full open position, first canopy switch  34  provides power to POS  2  winding of motor operated selector valve  44 , via first canopy switch  34 , when FULL OPEN switch  32  is selected to the DOWN TO CANOPY position. After motor operated selector valve  44  transitions to POS  2 , power is removed from POS  2  winding of motor operated selector valve  44  by the internal POS  2  switch and applied to open solenoid operated isolation valve  46  via FULL OPEN switch  32 . At approximately  90  degrees of door rotation, first canopy switch  34  is actuated thereby causing power to be removed from POS  2  of solenoid operated isolation valve  46 . Cargo door  10  continues to lower until it is stopped in the canopy position by ram locks, which are internal to lift mechanism  26 . As the operator removes his hand from FULL OPEN switch  32 , FULL OPEN switch  32  returns to the OFF position, which transfers power to POS  1  winding  50  of motor operated selector valve  44 , via door closed A switch  38 , until motor operated selector valve  44  moves fully to POS  1 . Since solenoid operated isolation valve  46  is closed and motor operated selector valve  44  is in POS  1 , a hydraulic block is provided that also hydraulically locks cargo door  10  in the canopy position.  
         [0030]    To close cargo door  10  from the canopy position, UP TO CANOPY switch  30  must be placed in the CLOSE position. Placing UP TO CANOPY switch  30  in the CLOSE position provides power to the POS  2  winding of motor operated selector valve  44 . When motor operated selector valve  44  is in POS  2 , power is removed from the POS  2  winding of motor operated selector valve  44  and transferred to solenoid operated isolation valve  46 . At this point the hydraulic block is removed and hydraulic pressure is supplied to remove the locks that are internal to lift mechanism  26  allowing cargo door  10  to close.  
         [0031]    During a closing operation, if cargo door  10  is in a position above and below the canopy position, when the operator removes his hand from either UP TO CANOPY switch  30  or FULL OPEN switch  32 , solenoid operated isolation valve  46  closes first and then motor operated selector valve  44  transitions from POS  2  to POS  1  to provide a hydraulic block to lock cargo door  10  in the intermediate position. Subsequent reapplication of either UP TO CANOPY switch  30  or FULL OPEN switch  32  to continue closing cargo door  10  causes motor operated selector valve  44  to transition from POS  1  to POS  2  to remove the hydraulic block and then solenoid operated isolation valve  46  is opened to apply door closing pressure.  
       Door Operator Indication System (see FIGS.  3 ,  4 ,  5 , and  6 )  
       [0032]    With particular reference to FIGS.  3 - 6 , door operator indication system  66  provides notification to crewmembers, either a door operator or maintenance personnel, that are operating cargo door  10 , concerning the status of cargo door  10  and its mechanisms. Indication is provided by two lighted switches  68  and  70  on door operator control panel  16  (FIG. 6). Electrical command signals to lighted switches  68 ,  70  is provided by four limit switches—a door latched A switch  74 , door latched B switch  76 , door locked A switch  78 , and door locked B switch  80 —on cargo door  10  and two limit switches—first canopy switch  34 , second canopy switch  36 , door closed A switch  38 , and a door closed B switch  82 —on the door opening of the fuselage.  
         [0033]    Lighted switches  68 ,  70  on door operator control panel  16  are specifically identified as CLOSED AND LATCHED switch  68 , UNLOCKED switch  70 , and an AURAL WARN DISABLE switch  84 . UNLOCKED switch  70  is a lighted momentary switch with four amber LED&#39;s. AURAL WARN DISABLE switch  84  is a lighted, guarded, alternate action switch with four amber LED&#39;s. CLOSED AND LATCHED switch  68  is a lighted momentary switch with four green LED&#39;s. The switch function of CLOSED AND LATCHED switch  68  and UNLOCKED switch  70  is used to provide a “press to test” check of the LED&#39;s to insure the LED&#39;s are working properly.  
         [0034]    When cargo door  10  is in a closed, latched, and locked position, both CLOSED AND LATCHED switch  68  and UNLOCKED switch  70  are extinguished on door operator control panel  16 . When cargo door  10  is unlocked, CLOSED AND LATCHED switch  68  and UNLOCKED switch  70  will illuminate on door operator control panel  16 . UNLOCKED switch  70  remains illuminated whenever cargo door  10  is unlocked. When cargo door  10  is open or unlatched, CLOSED AND LATCHED switch  68  will extinguish, and conversely it will illuminate when cargo door  10  is closed and latched. AURAL WARN DISABLE switch  84  is normally extinguished during normal door operations.  
         [0035]    Electrical wiring connects first canopy switch  34 , second canopy switch  36 , door closed A switch  38 , door unlocked switch  40 , and motor operated selector valve  44  to CLOSED AND LATCHED switch  68  and UNLOCKED switch  70  on door operator control panel  16  and to a dual logic system  86  of a Proximity Switch Electronics Unit (PSEU)  88 . PSEU  88  receives inputs from a cargo door hydraulic system pressure switch  90 , AURAL WARN DISABLE switch  84 , door closed A switch  38 , door closed B switch  82 , door latched A switch  74 , door latched B switch  76 , door locked A switch  78 , and door locked B switch  80  that sense the position of latch mechanism  22 , pull-in mechanisms  24 , the hydraulic pressure of the cargo door control system, and cargo door  10  itself.  
         [0036]    As described above and best seen in FIG. 4, door unlocked switch  40 , door latched A switch  74 , door latched B switch  76 , door locked A switch  78 , and door locked B switch  80  are each disposed on cargo door  10 . Along the bottom of the door opening in the fuselage are door closed A switch  38  and door closed B switch  82 . As seen in FIGS. 2 and 4, cargo door hydraulic system pressure switch  90  is installed in cargo door hydraulic system  200  to sense whether hydraulic pressure is being applied to cargo door  10  when it should not be (i.e., solenoid operated isolation valve  46  commanded or stuck in the energized position). The presence of a ground at any of these eight switches— 38 ,  40 ,  74 ,  76 ,  78 ,  80 ,  82 ,  90 —is registered as a TRUE (Logic  1 ) condition.  
         [0037]    Door locked A switch  78  and door locked B switch  80  are actuated in response to the lock and vent panel mechanism. Door locked A switch  78  and door locked B switch  80  provide positive indication to PSEU  88  when cargo door  10  is locked. Both door locked A switch  78  and door locked B switch  80  are located at the aft end location the locking and venting mechanism. If either or both of door locked A switch  78  and door locked B switch  80  indicate a cargo door not locked condition (Logic  0 ), amber UNLOCKED switch  70  on door operator control panel  16  will be illuminated.  
         [0038]    Door unlocked switch  40  is also actuated in response to the lock and vent panel mechanism. Door unlocked switch  40  functions as electrical interlock to door operator control panel  16  to interrupt electrical current from circuit breaker  28  when cargo door  10  is locked.  
         [0039]    Door latched A switch  74  and door latched B switch  76  are actuated in response to latch mechanism  22 . Door latched A switch  74  and door latched B switch  76  provide positive indication to PSEU  88  when cargo door  10  is latched. Door latched A switch  74  and door latched B switch  76  are disposed at opposing ends of latch mechanism  22 .  
         [0040]    Door closed A switch  38  and door closed B switch  82  are actuated in response to strikers (not shown) extending from the bottom edge of cargo door  10 . Door closed A switch  38  functions to interrupt electrical current to POS  1  of motor operated selector valve  44  and provides positive indication to PSEU  88  when cargo door  10  is closed (directly to PSEU  88  and via CLOSED AND LATCHED switch  68 ). Door closed B switch  82  also provides positive indication to PSEU  88  when cargo door  10  is closed. Door closed A switch  38  is installed at the forward end of the lower edge of the fuselage cutout and door closed B switch  82  is at the aft end.  
         [0041]    If either or both of door latched A switch  74  and door latched B switch  76  indicate a door not latched condition (Logic  0 ), or either or both of door closed A switch  38  and door closed B switch  82  indicate a door not closed condition (Logic  0 ), or cargo door  10  is unlocked (door unlocked switch  40  closed), then CLOSED AND LATCHED switch  68  on door operator control panel  16  will not be illuminated.  
         [0042]    AURAL WARN DISABLE switch  84  is provide on door operator control panel  16  to deactivate a takeoff configuration aural warning module  92  (FIG. 4) to enable aircraft  14  to be dispatched using minimum equipment list procedures, such as when control and indication system  20  has faults that can not be repaired at the current airport. When AURAL WARN DISABLE switch  84  is pressed to disable the aural warning from takeoff configuration aural warning module  92 , AURAL WARN DISABLE switch  84  will illuminate and remain illuminated until AURAL WARN DISABLE switch  84  is pressed again to enable takeoff configuration aural warning module  92 . Disabling takeoff configuration aural warning module  92  prevents subsequent faults in control and indication system  20  from causing an unnecessary rejected takeoff.  
       Flight Crew Indication System  
       [0043]    As best seen in FIG. 7, control and indication system  20  further includes a flight crew indication system  94 , which provides visual and aural warnings to the flight crew members when cargo door  10  is not fully closed, latched, and locked. To this end, PSEU  88  provides an electrical ground to illuminate a MASTER CAUTION warning indicator  96 , a DOORS warning indicator  98 , a MAIN CARGO warning indicator  100 , an OVERHEAD warning indicator  102 , and a PSEU warning indicator  104 . Aural annunciation (tone) is produced by takeoff configuration aural warning module  92 . As described above, AURAL WARN DISABLE switch  84 , which provides a logic input to PSEU  88 , is located on door operator control panel  16 .  
         [0044]    Dual logic system  86  of Proximity Switch Electronics Unit (PSEU)  88  checks the position of cargo door  10  via door closed A switch  38 , door closed B switch  82 , door latched A switch  74 , door latched B switch  76 , door locked A switch  78 , door locked B switch  80 , and cargo door hydraulic system pressure switch  90 . The logic for each channel is graphically illustrated in FIG. 5 and summarized in FIG. 8. When an unsafe configuration is detected, PSEU  88  provides a ground input (Logic  1 ) to corresponding MASTER CAUTION warning indicator  96 , DOORS warning indicator  98 , and/or MAIN CARGO warning indicator  100  and/or takeoff configuration aural warning module  92  in flight deck  18 . PSEU  88  has Built-In-Test-Equipment (BITE) to determine if there is a disagreement between the logic outputs of each channel. When an internal fault is detected, PSEU  88  provides a ground (Logic  1 ) to MASTER CAUTION warning indicator  96 , OVERHEAD warning indicator  102 , and/or PSEU warning indicator  104  in flight deck  18 .  
         [0045]    MASTER CAUTION warning indicator  96 , DOORS warning indicator  98 , and MAIN CARGO warning indicator  100  illuminate when cargo door  10  is not closed, not latched, not locked, or pressure is still applied. All three warning lights illuminate when either a single, or multiple non-redundant, or redundant switch indicates not closed, not latched, or not locked on the ground prior to advancing a left trust lever position  106  or a right thrust lever position  108  beyond  53  degrees, or  30  seconds after landing as detected by air/ground relay  42 . No indication is provided for new faults when a single or multiple nonredundant switch indicates not closed, not latched, or not locked while in-flight. MASTER CAUTION warning indicator  96  also illuminates when a single switch falsely indicates in either logic system a closed, latched, or locked. False indication is detected when cargo door  10  is unlocked, unlatched, and opened by checking to see that all ground signals (Logic  1 ) have transitioned to Logic  0  (i.e., open).  
         [0046]    If both door closed A switch  38  and door closed B switch  82  indicated not closed, or both door latched A switch  74  and door latched B switch  76  indicate not latched, or both door locked A switch  78  and door locked B switch  80  indicate not locked, and either trust lever is advanced beyond  53  degrees on the ground, then an aural warning is generated from takeoff configuration aural warning module  92 . This is in addition to illumination of MASTER CAUTION warning indicator  96 , DOORS warning indicator  98 , and MAIN CARGO warning indicator  100  warning lights. AURAL WARN DISABLE switch  84  is operated to disable takeoff configuration aural warning module  92 . If the aural warning has been disabled, dispatchable PSEU warning indicator  104  and OVERHEAD warning indicator  102  will illuminate when the pilots do a normal Master Caution Recall prior to takeoff.  
         [0047]    The present invention being thus described provides a warning indication system that can distinguish if the indication system is providing valid cargo door status so that unnecessary rejected takeoffs are not performed. In addition, the present invention provides a means whereby warnings for nonsignificant failures that occur during the takeoff roll and in flight, are identified and stored for subsequent display upon landing. The present invention still further provide a means to deactivate the aural warning if faults are detected in the warning circuit before flight, while simultaneously providing a visual warning to the pilots in flight deck  18  that deactivation of the aural warning is active.  
         [0048]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.