Abstract:
A security pocket door traverses within a security bulkhead wall that defines a pocket, within which the pocket door traverses, and a through passage to permit people, carts and luggage to pass. The pocket door has an upper door track mechanism and a lower door track mechanism that engages a corresponding upper and lower track mechanism of the bulkhead and floor, respectively. The bulkhead door locks with at least one solenoid with a locking pin that engages a hole in a tab of the pocket door. The locking pin creates a magnetic field with a magnet located in the tab to send a signal to the flight deck in order to indicate a closed and locked or an unlocked pocket door condition. When the pocket door is in its closed position, the door perimeter overlaps the bulkhead on at least three sides of the door and also overlaps with the floor.

Description:
FIELD OF THE INVENTION 
   The present invention relates to pocket door systems, and more specifically, to a flight deck security sliding pocket door system for use within an aircraft. 
   BACKGROUND OF THE INVENTION 
   Commercial aircraft manufacturers and their customers are increasingly interested in installing security devices aboard commercial aircraft. More specifically, one area of the security interest is related to cockpit, or flight deck, security and the systems in place to securely separate the flight deck from the passenger compartments of the aircraft. Additionally, Federal Aviation Administration (FAA) regulations have also been increasingly directed to the area of cockpit and flight deck security, and more specifically, to the area of flight deck door security. 
   While current cockpit doors are generally satisfactory for their applications, each is associated with its share of limitations. One major limitation of current cockpit doors, and interior aircraft doors in general, is their cumbersome characteristics during use. Since many current cockpit and interior doors are hinged so that they can swing in one or two directions, opening such a door can prove cumbersome on an aircraft given the use of floor space with seats, galleys and other necessary structures, and the limited space for people to move out of the path of such an opening door. The problem of opening a swinging, hinged door is compounded when a door user is carrying an item, pulling or pushing a cart, or toting or pulling a piece of luggage. Normally, the user or someone is touched by, or brushes against, a door when it is opened or closed. Alternatively, a user or another normally has to step around or at least move out of the way of an opening or closing door. 
   Another limitation of current interior and cockpit aircraft doors relates to their non-overlapping structure. That is, when a current hinged, swinging door is closed, a gap, regardless of how small, is realized around the perimeter of the door between the door and its surrounding structure, such as between the door and the bulkhead. This non-overlapping structure allows noise and air to pass around the door. 
   Yet another limitation of current interior and cockpit aircraft doors relates to their method of locking. Current swinging doors normally latch, or lock, opposite to the hinged side of the door when a user moves a mechanical latching device. These mechanical latch devices take on a variety of styles and methods of use and are susceptible to misalignment and preloading of the mechanisms. Additionally, these mechanical latches have an undesirable level of noise associated with them when they are used. 
   Still yet another limitation of many current cockpit doors is their less than optimum ballistic and intrusion resistance characteristics. Because of these less than optimum ballistic and intrusion resistance characteristics, some cockpit doors are limited in providing the desired ballistic and intrusion resistance characteristics desired by aircraft customers and the characteristics required by the FAA without heavy metallic inserts and edge treatments in the door and door frame. What is needed then is a device that does not suffer from the above limitations. 
   SUMMARY OF THE INVENTION 
   In accordance with the teachings of the present invention, a flight deck security pocket door system is provided that resists intrusion by people and that prevents small arms fire and shrapnel from passing through the door or perimeter edges. Additionally, the flight deck security pocket door system provides a reduction in latch complexity and can provide a weight reduction over current swinging security door systems and will provide improvements in ease of use. The flight deck security pocket door system includes a bulkhead wall with a doorway for the passage of people, wheeled serving carts, luggage, etc. The wall has an upper wall track mechanism on which the bulkhead door, which has an upper door track mechanism and a lower door track mechanism, traverses. The bulkhead door&#39;s lower track mechanism engages a floor track mechanism to permit movement on the floor track mechanism. 
   The system may have at least one solenoid that employs an engagement pin that engages a door latch attached to the bulkhead door to lock the door in its closed position. The upper door track mechanism engages the upper wall track mechanism while the lower door track mechanism engages the floor track mechanism. When the door is in its closed position, the perimeter of the door overlaps the bulkhead on three sides of the door, that is, because the sliding door fits within the wall, the bulkhead wall actually overlaps the door. This overlap provides added strength to prevent intruders and objects from breaching the door, as opposed to a swinging door that fits within a wall opening and merely fills the opening typically with minimum support from door jambs and door stops. Furthermore, when the door is in its closed position, a bottom edge of the door may reside within the floor or threshold, thereby providing overlap of the door below at the level of the floor. 
   The flight deck security pocket door system may have a second locking solenoid that employs a second locking pin that engages the door latch for redundancy. The door latch may be engaged by the first pin from a top of the door latch and the second pin may engage the door latch from the bottom of the door latch. The door latch may be a pawl-like device that pivots about a pin in the door or it may be a solid non-pivoting attachment. The first pin of the first solenoid and the second pin of the second solenoid may be magnetic to magnetically interact with at least one magnet within the door latch to indicate a closed and locked door condition to the flight deck area or other location. The upper wall track mechanism in the bulkhead wall has a removable section to facilitate installation and removal of the bulkhead door. 
   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. The features, functions, and advantages can be achieved independently in various embodiments of the present inventions or may be combined in yet other embodiments. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
       FIG. 1  is a perspective view of an aircraft fuselage depicting locations of security sliding pocket door systems, according to teachings of the present invention; 
       FIG. 2  is an elevation view of the security pocket door system, according to teachings of the present invention; 
       FIG. 3  is a perspective view of the security pocket door system showing an example of its removable track system, according to teachings of the present invention; 
       FIG. 4  is an elevation view of the security pocket door showing the areas of overlap of the pocket door with the surrounding bulkhead; 
       FIG. 5  is a top view of the security pocket door system depicting the overlap of the pocket door with the surrounding bulkhead; 
       FIG. 6  is a perspective view of the security pocket door system depicting areas of rolling, guiding or tracking mechanisms; 
       FIG. 7  is an edge view of a top rolling mechanism of the security pocket door system; 
       FIG. 8  is an edge view of a top rolling mechanism of the security pocket door system; 
       FIG. 9  is an edge view of a top rolling mechanism of the security pocket door system; 
       FIG. 10  is an edge view of a bottom rolling mechanism of the security pocket door system; 
       FIG. 11  is an edge view of a bottom rolling mechanism of the security pocket door system; 
       FIG. 12  is an edge view of a bottom rolling mechanism of the security pocket door system; 
       FIG. 13  is an edge view of a bottom rolling mechanism of the security pocket door system; 
       FIG. 14  is an elevation view of a security pocket door system utilizing a spring bumper on a rod above the pocket door; 
       FIG. 15  is an edge view of a solenoid mechanism used to lock the pocket door within the bulkhead; 
       FIG. 16  is a side view of a biased locking lever and solenoid pin of the pocket door system; 
       FIG. 17  is a side view of a dual solenoid locking mechanism and locking tab of the pocket door depicting indicator magnets within the door tab; 
       FIG. 18  is a perspective view of the security pocket door system utilizing linear bearings, a spring bumper, a threshold and lights in a doorway having a step-down into a flight deck area; 
       FIG. 19  is a cross-sectional view of the bottom of the security pocket door of  FIG. 18  depicting a clean-out slot in a threshold and how the security door is positioned relative to the step and depicting structure that safeguards against a projectile; 
       FIG. 20  is a cross-sectional view of the bottom of the security pocket door of  FIG. 18  recessed below the top of the threshold and depicting a clean-out slot in a threshold and how the security door is positioned relative to the step depicting structure that safeguards against a projectile; 
       FIG. 21  is a side view of a finger tab and grab handle of the security pocket door; 
       FIG. 22  is a side view of a solenoid arrangement depicting the finger tab engaging the solenoid locking pins in a dual solenoid arrangement; 
       FIG. 23  is a perspective view of a pocket door showing a retraction tab and a mechanical linkage of the security pocket door system; 
       FIG. 24  is a side view of a wall-mounted spring bumper depicting how a pocket door rebounds from the bumper upon closing the pocket door past the alignment point with the solenoid pins; 
       FIG. 25  is a side view of a door latching mechanism within a pocket door tab that depicts how the latch will retract when activated with a knob or slide; 
       FIG. 26  is a side view depicting the motion of the linkage mechanism of  FIG. 25 ; 
       FIG. 27  is a perspective view depicting the security pocket door and cleanout panels in the surrounding bulkhead; 
       FIG. 28  is a cross-sectional view of the bottom of the security pocket door and threshold and depicting structure that safeguards against a projectile; 
       FIG. 29  is a view of the bottom of the security pocket door depicting guides and pads for the security door within the bulkhead; 
       FIG. 30  is a perspective view of the security pocket door depicting a panel to permit removal of the security pocket door; 
       FIG. 31  is a perspective view of the security pocket door depicting a panel to permit removal of the security pocket door; 
       FIG. 32  is a perspective view of the security pocket door depicting a panel to permit removal of the security pocket door; 
       FIG. 33  is a perspective view of the security pocket door depicting the location of a hanging mechanism behind the door removal panel of the security pocket door; 
       FIG. 34  is a perspective view of the security pocket door depicting the removal of the door using a hinged bearing device; and 
       FIG. 35  is a perspective view of the security pocket door depicting an example of the hinged bearing device of  FIG. 34 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. The teachings of the embodiments of the present invention can be applied in a multitude of situations where a security pocket door is required. For simplicity, the teachings of the present invention are depicted and described in reference to an aircraft application. 
   Turning now to the preferred embodiments of the teachings of the present invention,  FIG. 1  depicts an aircraft  10  noting the locations of security pocket door systems  20 . It will be noted that while the following description references an aircraft, that the security pocket door can be used on various older types of mobile platforms such as busses, trains, marine vessels, or wherever there is a need to secure a designated area from individuals not authorized to enter the designated area. 
   In the present example, the security pocket door  20  can be employed in the front of the aircraft, to separate the flight deck from the passenger cabin, or anywhere in the passenger cabin to separate groups of passengers. In  FIG. 1 , the security pocket door system  20  is depicted in the front of the aircraft and the rear of the aircraft. However, for purposes of this detailed description of embodiments of the present invention, the security pocket door will be discussed with respect to its location in the front of the aircraft  10  where the security pocket door system  20  separates the flight deck, or cockpit, from the balance of the aircraft fuselage normally occupied by passengers. 
   Turning now to the details of the teachings of the first embodiment,  FIGS. 2-6  depict a removable security pocket door system  20 .  FIG. 2  depicts a security pocket door  22  residing within a bulkhead  24  of the aircraft  10 . The security pocket door  22  traverses within the bulkhead  24  by riding on a top track hanger  32 . The security pocket door  22  has at least two door hangers  28  that interface with the top track hanger  32  by sliding or rolling on the top track hanger  32 . In this first embodiment of the security pocket door system  20 , a removable top track section  30  fits within the top track hanger  32 , the removable top track section  30  being removable from the top track hanger  32  to facilitate installation and removal of the security door  22 . 
   In  FIG. 2 , the security door  22  is depicted with a hidden or dashed line. When the security door  22  is moved to its closed position, from its open position, a finger tab  36  becomes situated between a top solenoid  38  and a bottom solenoid  40 . When the solenoids  38 ,  40  are electrically de-energized, they permit the pocket door  22  to open, that is, the solenoid pins retract. When the solenoids  38 ,  40  are energized, the pocket door becomes locked. The locking of the security door  22  is accomplished when the finger tab  36  is engaged by solenoid pins, to be discussed later. The security door  22  also has a bottom track  42  within which the bottom portion of the security door  22  may traverse. The security door  22  is provided with an armored, wide angle peep hole  34 , and in some instances multiple peep holes, so personnel from the flight deck side of the security door  22  can look through the peep hole(s)  34  toward the passenger cabin side of the security door  22 . The security door  22  can be provided with at least one decompression panel  45  that when released due to a pressure differential between each side of the door, serves as a path for air to flow between the passenger cabin and the flight deck should the airplane experience an explosive decompression due to a breach in the pressurized section of the fuselage. The security door  22  also may be provided with an escape panel  46  that when released, will allow the flight deck occupants entry into the passenger cabin should the security door  22  become jammed in an emergency. Finally, the security door  22  is provided with a deadbolt that is operated with a key from the passenger cabin side or a lever from the flight deck side which, when activated, will make the key inoperable. The deadbolt will engage the top track section  32  when the bolt is extended. 
     FIG. 3  depicts the removable top track section  30  in its removed state from the top track hanger  32 , which is situated directly below a portion of the bulkhead  24 . A pocket  26  is the space within which the security door  22  traverses on a bottom track  42 . In this embodiment, the top track hanger  32  has just one removable top track section  30 , although it is conceivable that the top track hanger  32  may have more than one removable top track section  30 . 
   Turning to  FIGS. 4 and 5 , a feature of the security pocket door  20  is shown. That feature is an overlap portion of the security door  20  between the bulkhead  24  and the perimeter of the security door  22 . Although the overlap dimension can be whatever dimension is desired, for purposes of this embodiment, the overlap of the door within the bulkhead  24  is approximately one inch (25.4 mm). In this fashion, light can not be seen between the interface of the bulkhead  24  and the security door  22  and the ballistic armor  43  integral to the security pocket door overlaps the ballistic armor  44  in the security bulkhead. 
     FIG. 6  denotes the locations of the top and bottom rolling mechanisms that enable the security door  22  to traverse within the bulkhead  24 . Examples of top rolling mechanisms employable on the security pocket door  20  are depicted in  FIGS. 7-9 . It should be noted that  FIGS. 7-9  depict potential rolling mechanisms of the security pocket door  20 , they are in no way the only top rolling mechanisms employable with the security pocket door  20 . In fact, a variety of sliding mechanisms exist as potential methods of permitting the security door  22  to traverse within the bulkhead  24 . 
     FIG. 7  depicts a first top rolling mechanism  50 . The first top rolling mechanism  50  employs a top door hanger  52 , to which a top door wheel  54  is attached. The top door wheel  54  is notched in a V-shape and has a first door wheel bevel  56  and a second door wheel bevel  58 . The top door wheel  54  rides on a top track rail  33 , that is, the top door wheel  54  bevels  56 ,  58  rides upon the bevels of the top track rail  33 , which is part of the top track hanger  32 . The top door hanger  52  is attached to the top surface of the security door  22 . 
   Turning to  FIG. 8 , a second top track rolling mechanism  60  is depicted. This rolling mechanism employs a top C-channel  62  that encompasses or surrounds a top wheel  66  that rides within the interior portion of the top C-channel  62 . The top wheel  66  is mounted on a vertical shaft  64  that is mounted to the top portion of the security door  22 . While the top track rolling mechanism  50  of  FIG. 7  depicts a rolling methodology in which the weight of the door may be entirely supported by the top track hanger  32 , while the top track rolling mechanism  60  of  FIG. 8  depicts a top rolling mechanism that merely guides the top wheel  66  and does not support any weight. 
     FIG. 9  depicts a third top rolling mechanism  70 . This rolling mechanism employs a V-shaped top wheel  76  that rides against a top V-shaped track  72 . A top wheel  76  is mounted on a horizontal shaft  74 , the horizontal shaft  74  mounted within a groove cut into the top portion of the security door  22 . The top wheel  76  has a dual bevel arrangement to form the recessed V-portion of the top wheel  76  that rides on the top V-shaped track  72 . The top wheel  76  has a first door wheel bevel  56  and a second door wheel bevel  58 . 
   As can be seen in  FIGS. 7-9 , the security door  22  overlaps or protrudes into the bulkhead  24  for added security. A major advantage between this security door  22  and a conventional door that swings open on hinges (not shown) is that the security pocket door  22  provides overlap. A conventional hinged door normally exposes its hinges or mechanism by which the door opens, on a side of the door. Additionally, a hinged door may also expose at least a bolt, on a side of the door opposite the hinges. However, with this security door  22 , the rolling mechanisms depicted in  FIGS. 7-9  are not visible to a person from either side of the security door  22 . Additionally, the locking mechanisms of the security door  22  can not be seen by the door user and gaps around the door through which ballistic fragments can pass are eliminated. 
     FIGS. 10-13  depict mechanisms by which the security door  22  may traverse within a floor  25  or on a bottom door track of the aircraft  10 . Turning to  FIG. 10 , the security door  22  is shown situated within the floor  25  or threshold (not shown) of the aircraft, the security door  22  being accommodated by three rollers  82 ,  84 ,  86 . The first side roller  82  and the second side roller  84  maintain the lateral position of the security door  22  when it is rolling within the floor  25 . A bottom roller  86  bears at least a portion of the weight of the security door  22 , depending upon which top rolling mechanism is used, as the door traverses within the floor  25  of the aircraft. The rollers  82 ,  84 ,  86  may be mounted in or to the security door  22  or they may be mounted in the floor  25  that surrounds the bottom of the security door  22 . 
   Turning to  FIG. 11 , a second bottom rolling mechanism  90  is depicted in which the security door  22  utilizes a bottom roller  92  situated on a horizontal shaft  94 , the ends of which are mounted within a groove of the security door  22 . In one variation of the embodiment, the bottom roller  92  rides upon an insert  96 . The insert  96  may be made from any material that will facilitate a low rolling friction relationship between the bottom roller  92  and the insert  96 . The bottom roller  92  rides upon an insert surface  98  of the insert  96 . 
   Turning to  FIG. 12 , a third bottom rolling mechanism  100  is depicted. This rolling mechanism is similar to the second bottom rolling mechanism  90 ; however, the bottom roller  102  has a notched V-surface about its periphery. The periphery of the bottom roller  102  has a first bevel  108  and a second bevel  109  that form the V-shaped periphery. This V-shaped periphery rides upon a peak  107  of an insert  106 . The bottom roller  102  utilizes a horizontal shaft  104  similar to the horizontal shaft  94  of the second bottom rolling mechanism  90 . Similarly, the insert  106  serves a similar purpose as the insert  96  of the second bottom rolling mechanism  90 . An advantage of the third bottom rolling mechanism  100  is that the V-shaped periphery of the bottom roller  102  with its first and second bevels  108 ,  109 , ride upon the peak  107  of the nylon or other low rolling resistance material insert  106 . With the bottom roller  102  riding upon the peak  107 , the security door  22  is able to maintain its position within the floor  25 , that is, the security door  22  is better able to maintain its position parallel to the floor  25 , within the bottom track. 
   Turning to  FIG. 13 , a fourth bottom mechanism  110  is shown. This mechanism  110  employs a bottom blade  114  that fits within a bottom track  116 . The bottom blade  114  is part of the overall bottom door slider  112  that provides ballistic protection for the bottom door gap and is made from stainless steel, titanium or a similar ballistic resistant material. As can be seen from  FIG. 13 , the portion of the bottom door slider  112  that is parallel to the top surface of the floor  25  is able to ride upon the top surface of the floor  25  if they should come into contact. Similarly, the bottom blade  114  that traverses within the bottom track  116  is permitted to bump against the walls of the bottom track  116 . The bottom track surface  118  is permitted to come into contact with the bottom surface of the bottom blade  114 ; however, in an ideal situation, the bottom door slider  112  will not contact the floor  25  of the aircraft because the security door  22  hangs from the top track hanger  32 . Since an ideal traversing relationship between the bottom door slider  112  and the bottom track  116  may not always be maintained, the bottom door slider  112  may be coated with a material that will facilitate sliding contact between the bottom door slider  112  and the bottom track  116 . As an alternative, the bottom track  116  may be coated with a material that will facilitate sliding contact between the slider  112  and the bottom track  116 . A further alternative would be for both the slider  112  and bottom track  116  to be coated with a low friction material. Materials that may be suited to the bottom door slider  112  and/or bottom track  116  are materials such as nylon, polytetrafluoroethylene (PTFE) or ultra-high molecular weight polyethylene (UHMWPE); however, the materials are not limited to such. 
   With reference to  FIG. 14 , a security pocket door is depicted that employs a bumper mechanism  120 . As can be seen from  FIG. 14 , the security door  22  has attached to its top, linear bearings  126  that ride upon a rod  124 . When the security door  22  is moved toward its closed position, a bumper plate  128 , attached to an end surface of a bumper spring  129 , that is in turn attached to the bulkhead, contacts the security door. When the security door  22  contacts the bumper plate  128  and bumper spring  129 , it is able to decelerate the security door  22  to bring the door to a halt. When the security door  22  is in its normally-closed position, the security door is in contact with the bumper plate  128  at the same time that the finger tab  36  aligns itself with the top solenoid  38  and bottom solenoid  40 . In this manner, if the security door  22  is forced farther in the closed direction, the bumper plate  128  and the bumper spring  129  engagement will cause the spring to generate a restoring force and move the door back to its normally closed position and align the finger tab  36  with the solenoid pins. When the finger tab  36  becomes aligned between the top solenoid  38  and bottom solenoid  40 , the top solenoid pin  138  and bottom solenoid pin  140  can engage holes or a cavity in the finger tab from opposite sides of the finger tab. At the time of this engagement of the solenoid pins  138 ,  140  with the finger tab  36 , the door edge  123  will overlap with the bulkhead by approximately one inch. That is, the door edge  123  will lie one inch beyond the door opening  122  with respect to the bulkhead. 
     FIG. 15  shows an edge view of an alternate single solenoid arrangement in which the pin  130  of the solenoid  40  engages a pawl  132  instead of the finger tab  36 . In this fashion, the solenoid  40  can be located in other areas of the bulkhead, adjacent the door not just at the location of the door tab  36  for example. With this arrangement, a user need only move the security door  22  by employing the door handle  127  to maneuver the door over the solenoid  40 . The pin  130  and pawl  132  can be disengaged by a mechanical means or by de-energizing the solenoid  40 . 
     FIG. 16  shows a side view of the single solenoid alternate locking mechanism located within the security door  22 . The locking mechanism employs a pawl  132  and a pawl spring  134 . Using this locking mechanism, the pawl  132  is normally in a horizontal position relative to the floor of the aircraft. When the door is moved to its closed position, the pawl  132  engages or comes in contact with a pin  130  of a solenoid. Upon the pawl  132  engaging the pin, because the pawl has a bevel cut onto its leading face, the pawl  132  is forced away from the pin  130  until the pin  130  aligns itself with a pawl hole  133  within the pawl  132 . Upon this alignment of the pin  130  with the pawl hole  133 , the pawl  132  is able to drop onto the pin  130  to lock the security door  22 . The pawl  132  is biased by a pawl spring  134  into its horizontal position while the pawl  132  pivots about a pawl pivot pin  136 . In order to unlock the security door  22 , the pin  130  must be withdrawn from the pawl hole  133 . This withdrawal of the pin  130  from the pawl hole  133  would normally be accomplished by a solenoid; however, other means such as manually sliding the pin  130  or using a motor (not shown) are possible. A lever-action to release the pin is also feasible. 
     FIG. 17  depicts a dual solenoid arrangement in which the top solenoid  38  employs a top solenoid pin  138  and the bottom solenoid  40  employs a bottom solenoid pin  140 , which both engage the finger tab  36 . Within the finger tab  36  lies a top solenoid magnet  142  and a bottom solenoid magnet  144 . These solenoid magnets  142 ,  144  are used to detect the presence of their respective solenoid pin in order to send an electric signal to the flight deck to notify the flight crew that the security door  22  is in its closed and locked position with the solenoid pins  138 ,  140  engaged. When the solenoid pins  138 ,  140  are not each proximate to their respective magnet, an electrical locking signal is not sent, or a different signal is sent to the flight deck to indicate an unlocked state of the pocket door  22 . 
     FIG. 18  depicts a perspective view of a security door  22  showing its position outside of the bulkhead  24 , in a normally-closed position. As can be seen, the security door  22  rides upon the rod  124  using linear bearings  126 . The bumper plate  128  is shown attached to the bumper spring  129 . An end plate  146  is located at the opposite end of the bumper spring  129  as the bumper plate  128 . As can be seen in  FIG. 18 , the security door  22  is employed at a step down location on the aircraft floor. This location is typical of some large commercial aircraft where the flight deck is located at a lower or higher level than its adjoining compartment. That is, the security door  22  separates areas within the aircraft having different floor levels. It is also possible that the security door  22  can be used to separate compartments having the same floor level, including areas of an aircraft not involving a flight deck. Additionally, the security pocket door system  20  may be used on non-passenger aircraft, such as cargo aircraft. 
     FIG. 19  depicts a security door  22  employed at a step down location of the aircraft floor. To situate the security door  22  at such a location, a threshold  150  is employed. The threshold  150  acts as a platform upon which the security door  22  rides. The security door  22  employs a bottom blade  114  along the bottom surface of the security door  22 . The bottom blade  114  is situated within a track groove  156  that also acts as a cleanout slot  158 . Because the bottom metallic blade  114  is coated with a material such as plastic, and the threshold  150  is made of a ballistic resistant metal material coated with a material such as plastic in the area of the track groove  156 , the bottom blade  114  is easily able to slide upon the threshold  150  because of the low-friction coefficient between the two materials. 
   In the arrangement shown in  FIG. 19 , the security door  22  largely rides above the threshold  150 . That is, the entire security door  22 , except for the bottom blade  114 , is situated above the threshold  150 . The security door  22  is also located above the passenger cabin floor  162  and the flight deck floor  160 . No tracks are located within the flight deck floor  160  or passenger cabin floor  162  in this arrangement. Low intensity lights  152  and black and yellow diagonally striped warning tape  148  are shown situated in a recessed area within the threshold  150  on the flight deck side of the threshold  150 . In a similar fashion, low intensity lights  154  and black and yellow diagonally striped warning tape  147  are situated on the passenger side of the threshold  150 . The lights  152 ,  154  and tape  147 ,  148 , may be situated within a recession or located on top of the surface of the threshold  150 . Flight deck carpet  163  may either abut the threshold  150  or be located under the threshold  150  on the flight deck side of the threshold  150 . Likewise, passenger cabin carpet  164  may abut the threshold or be located under the threshold  150  on the passenger side of the threshold  150 . Finally, from  FIG. 19 , the location of the bulkhead  24  can be seen over the step  159  and accompanying threshold  150 . Finally, in this embodiment, a projectile  168  is shown with a potential projectile path  169  that might be encountered should such a projectile be directed toward the door&#39;s floor structure. 
     FIG. 20  depicts an arrangement of the security door  22  and its accompanying bulkhead  24  over a step  159 . Like  FIG. 19 , the step  159  is a division point between the flight deck floor  160  and the passenger cabin floor  162 . In this arrangement, the threshold  151  is designed differently than the threshold  150  of  FIG. 19 . The threshold  151  is designed such that the security door  22  fits within a recession or groove of the threshold  151 . Again, the bulkhead  24  is situated over the step  159 , while the security door  22  traverses within the bulkhead  24 . This threshold  151  has a flared clean out slot  166 . The clean out slots permit debris such as paperclips, lint and small particles of dirt, etc., to fall beyond the track groove  156  to a location under the threshold  151 . 
   The security door is shown with a bottom blade  114  that rides within and makes contact with the threshold  151 . Similar to the embodiment shown in  FIG. 19 , the embodiment shown in  FIG. 20  depicts flight deck carpet  163  that either abuts the threshold  151  and/or is located under the threshold  151 . Likewise, on the passenger cabin side of the security door  22 , passenger cabin carpet  164  abuts against the threshold  151  and/or is located under the threshold  151 . Low intensity lights  152  and warning tape  147  are located adjacent to the security door  22  on the flight deck side while low intensity lights  154  and warning tape  148  are located on a passenger side of the security door  22  adjacent to the security door  22 . Finally, in this embodiment, a projectile  168  is shown with a potential projectile path  169  that might be encountered should such a projectile be directed toward the door&#39;s floor structure. 
     FIG. 21  depicts a security door finger tab  36 , which is attached to the edge of the security door  22 . The finger tab  36  is employed when a door operator uses his or her thumb  172  or a finger and places it into the groove or recession  170  of the finger tab  36  and applies force in the direction of arrow  174 . The force supplied by a user&#39;s thumb  172  enables the door to move towards its final closed position. The grab handle  177  with a recessed portion  178  is used to complete the movement to the final closed position at which the finger tab  36  lies between the top solenoid  38  and bottom solenoid  40 . When the finger tab  36  is in such a position, the top solenoid pin  138  and the bottom solenoid pin  140  are positioned to engage the finger tab  36 . 
     FIG. 22  depicts the arrangement within the finger tab  36  showing the pawls  145 ,  146  which upon contact with the pins  138 ,  140  pivot as shown by arrows  135 ,  136 . Springs  175 ,  176  return the pawls  145 ,  146  to their original positions once the pins  138 ,  140  align with the holes  187 ,  189  in the pawls thus locking the pins in place within the finger tab  36 . 
     FIG. 23  depicts yet another embodiment of the security door  22 . More specifically,  FIG. 23  depicts a linkage opening mechanism  180 . The linkage opening mechanism  180  utilizes a central linkage bar  182  and a door handle  127  to permit the unlocking of the security door  22 . The unlocking is accomplished by the central linkage bar  182  being connected to the operative workings within the finger tab  36 . 
     FIGS. 25 and 26  depict the operative workings of the mechanical linkage opening mechanism  180 .  FIG. 25  depicts an upper linkage bar  184   p  and a lower linkage bar  186   p , each of which moves toward each other when the central linkage bar  182   p  has a force applied to it in the direction of arrow  183  ( FIG. 25 ).  FIG. 26  depicts the movement of the linkage bars of the linkage opening mechanism  180 . More specifically, when a force is applied such as the force in the direction of arrow  183  of  FIG. 25 , the central linkage bar  182   p  moves to a new position depicted by position  182 . Because of the movement of the central linkage bar  182   p , the upper linkage bar  184   p  and the lower linkage bar  186   p  move from their pre-movement positions depicted by  184   p  and  186   p , respectively, to their post-movement positions,  184  and  186 . Central linkage bar  182   p  moves from its pre-movement position  182   p  to its post-movement position  182  as a result of its connection to and activation of door handle  127  such as by turning or sliding. 
     FIG. 27  is a perspective view of the security pocket door system depicting clean out panels  188 ,  190  in the bulkhead  24  to remove trash and dirt from within the bulkhead  24 . In this embodiment, it can be seen that the security door  22  rides upon the rod  124  using linear bearings  126 . Also, the security door  22  has an armored peep hole  34 , deadbolt  41 , a grab handle  177 , a decompression panel  45  and an escape panel  46 . 
     FIG. 28  is a cross-sectional view of the bottom of the security pocket door of  FIG. 27 .  FIG. 28  shows how the security door  22  fits within a threshold  193  on an even surface with no step. The security door  22  essentially divides the threshold  193  into a flight deck side  192  of the threshold  193  and a passenger cabin side  198  of the threshold  193 , with part of the threshold connecting the sides  192 ,  198  under the security door  22 . This embodiment depicts contact pads  194 ,  196  that can be made of a low friction material to promote sliding of the door on such pads. The material is typically nylon or another plastic, such as UHMWPE, that will promote low friction contact between the security door  22  and such pads  194 ,  196 . The carpet  195  typically abuts each side of the threshold or is embedded under each side  192 ,  198  of the threshold  193 . Because part of the security door  22  lies below the surface of each side  192 ,  198  of the threshold  193 , the security door  22  is able to provide overlap security protection in conjunction with the threshold  193 . This design provides increased protection from an intruder or a projectile  199  compared to standard, hinged doors. It should be noted that  FIG. 28  depicts a cross-sectional view taken at the edge of the door opening, that is, at the threshold  193  of the door. 
     FIG. 29  is a cross-sectional view of the bottom of the security pocket door  22  that lies within bulkhead  24  and fits within the bottom track  197 . The bottom track  197  is made from a metallic material and serves as a guide for the lower edge of the security door  22 . This cross-sectional view is taken at an area away from the threshold  193  of the door. Similar to the threshold area,  FIG. 29  depicts a flight deck side contact pad  194  and a passenger cabin side contact pad  196  within the bottom track  197 . Again, these contact pads  194  and  196  are commonly made from a low friction plastic material such as nylon or UHMWPE. 
     FIGS. 30-35  depict a removable security pocket door system  200 . The system employs a security door  202  that traverses within a bulkhead  204  by using hinged linear bearings  208  that ride on a rod  206 . From its installed position of  FIG. 30 , the removal of the security door  202  will be explained using  FIGS. 31-35 .  FIG. 31  depicts the security door  202  being moved in the direction of arrow  212  on rod  206  by employing the hinged linear bearings  208 . Upon or after moving the security door  202 , the hinged or removable bulkhead panel  210  is manually or automatically lifted in order to provide access to the linear bearings  208  of the security door  202  to remove the security door  202  from its pocket. Typically, such a panel  210  is closed and locked in place using a lock that can only be accessed by airline maintenance personnel and is typically located on the flight deck side of the door. After raising the bulkhead panel  210 , the threshold  216  is removed from its location within the doorway. Then, the security door  202  is moved in the direction of arrow  218 , the security door  202  still riding on its hinged linear bearings  208 . 
     FIG. 33  depicts the security door  202  in its door opening along with the bulkhead panel  210  in its upright and opened position. With the security door  202  in this position, the hinged linear bearings  208  are exposed to the person removing the security door  202 .  FIG. 34  depicts the security door  202  being moved from the rod  206  upon which the security door  202  rides. The security door  202  is swung in the direction of arrow  224  to complete its removal from the pocket within the bulkhead  204 .  FIG. 35  is an enlarged view of the hinged linear bearing  208  in its opened position. Upon opening or hinging the linear bearing  208  about its hinge axis  222 , the individual bearings  220  are removable from their position against the rod  206  on which the bearings  220  ride. 
   While various preferred embodiments have been described, those skilled in the art will recognize modifications or variations which might be made without departing from the inventive concept. The examples illustrate the invention and are not intended to limit it. Therefore, the description and claims should be interpreted liberally with only such limitation as is necessary in view of the pertinent prior art.