Abstract:
An operation mechanism adapted for activating a deceleration device for decelerating an opening movement of a door. The operation mechanism features a first mode of operation and an second operation mode. In the first mode of operation the operation mechanism allows free rotation of the door, when the operation mechanism is loaded by an impulse of the door below a predetermined threshold value. In the second mode of operation when the operation mechanism is loaded by an impulse of the door above the predetermined threshold value the operation mechanism decelerates free rotation of the door by connecting the door to the deceleration device which will then decelerate the acceleration of the door.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 60/780,337 filed Mar. 8, 2006, the disclosure of which is hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to safety systems aboard an aircraft. In particular, the invention relates to an operation mechanism adapted for activating a deceleration device for decelerating an opening movement of a door in the event of a cockpit decompression. Moreover, the invention relates to a cockpit door arrangement comprising such an operation mechanism and to a use of such an operation mechanism aboard an aircraft. 
     The cockpit door aboard an aircraft provides the primary means of dissipating pressure from the cabin to the cockpit during a cockpit decompression case. A cockpit decompression case may occur as a minimal opening involving relatively slow bleed of pressure up to a maximum opening (as defined by aviation authorities) involving a rapid loss of pressure. To ensure that the delta pressure build up upon the monuments and structure that form the physical barrier between the cabin and cockpit does not exceed the structural limitations, the cockpit door must release and open to a specific venting area within a short time frame. Delay of the door to provide adequate venting may result in catastrophic structural failure. 
     The total time frame for the door to provide an effective venting area may be defined as the time [ms] for releasing the door lock and the time [ms] for rotating the door open, for example to an opening angle of more than 80°. 
     To satisfy certain certification requirements defined by aviation authorities, it has to be demonstrated that an aircraft can survive a decompression case without subsequent loss of essential structure/equipment and life. For example, JAR 25.365(e) (2) specifies that the aircraft structure must be able to withstand the depressurization caused by an instant opening of a predetermined area in the pressurized shell, at any operating altitude. 
     From the beginning of a cockpit decompression event to the point of door lock release delta air pressure is acting upon the door, as time from the decompression event increases, so the delta air pressure load upon the door increases. The delta air pressure load causes the door to rotate open and accelerate, imparting kinetic energy into the door. In this connection, the resultant kinetic energy is dependant upon the air pressure load over time and the moment of inertia (MOI) of the door. This means that the slower the door is unlocked the higher the delta air pressure load at the point of release and that the higher the MOI of the door the longer the duration of (high) air pressure upon the door. Both factors increase the final kinetic energy of the door. Thus cockpit doors that are compliant with the post 9/11 security rules have a high kinetic energy due to the reinforced construction of the door. 
     Therefore, the cockpit doors should unlock rapidly and rotate through to a minimum venting area (for example more than 80°) as quickly as possible in the event of a cockpit decompression. 
     Once the door has rotated open sufficient to provide effective venting it must be decelerated, wherefore the energy present in the door must be dissipated without the door detaching (from its hinges) and without damage to the airframe. In particular, since a seat may be installed in the path of the rotating door, it must be ensured that no injuries will be caused to a flight crew member on that seat. Otherwise, without an effective means of energy dissipation, the door, once it has passed 90 degrees, will collide with the seat causing potential injury to occupant and possible detachment of the seat and/or detach the door from its hinges, causing unacceptable structural/equipment damage and possible crew injury. 
     The energy present in the door must be absorbed without adversely affecting the cockpit wall pressure difference. Allowing the door to rotate open unhindered to the minimum free venting area would advantageously limit the pressure difference load upon the cockpit wall. However the distance to decelerate the door before impact with the adjacent seat is minimal and amounts to approximately 13° of rotation in A 380 aircraft only. In this case, the resultant equivalent static reaction load applied at the centre of area of the door would be in excess of 4500 daN (4.500 kg), whereby the door as well as the adjacent seat might be damaged. 
     SUMMARY OF THE INVENTION 
     Amongst other things, it may be an object of the present invention to provide a realization for controlling and reducing the end energy of a cockpit door. 
     Amongst other things, this object may be met by an operation mechanism which is adapted for activating a deceleration device for decelerating an opening movement of a door, which operating mechanism comprises a pivot lever arrangement inter alia. Besides the pivot lever arrangement, the operation mechanism comprises a pivot arm arrangement which is located in the track of travel of the door and which is coupled to the pivot lever arrangement. In addition to these pivot arm and pivot lever arrangements, the operation mechanism of the present invention comprises a damping arrangement, which is adapted to block rotation of the pivot lever arrangement. Finally, the operation mechanism comprises first and second engagement means, wherein the first engagement means may be attached to a belt of the deceleration device and wherein the first engagement means may be concealed by the pivot arm arrangement and detachably mounted thereon. The second engagement means is located at an edge portion of the door and is designed to engage with the first engagement means. For example, the first engagement means may be designed as a buckle comprising an opening, which may engage with a hook of the second engagement means. Naturally, in contrast thereto, the hook may be located at the first engagement means whereas the second engagement means may be provided with an opening being adapted to engage with the hook on the first engagement means. 
     Since the operation mechanism of the present invention must be adapted to be used in the event of a cockpit decompression as well as during normal flight conditions, the operation mechanism features a first mode of operation and a second mode of operation, wherein the first mode of operation takes place during normal conditions whereas the second mode of operation takes place during the event of a cockpit decompression. During the first mode of operation, the damping arrangement is adapted to allow rotation of the pivot lever arrangement, when the pivot lever arrangement is loaded by an impact due to a first opening impulse below a predetermined threshold value, which is imparted by the door edge during an opening movement of the door. 
     In contrast thereto, during the second mode of operation, the damping arrangement is configured to block a rotation of the pivot lever arrangement when being loaded by an impact due to a second opening impulse above the predetermined threshold value, which may be delivered from the door edge to the pivot lever arrangement via the pivot arm arrangement. Due to the first impulse delivered from the door edge to the pivot arm arrangement in the first mode of operation, the pivot arm arrangement rotates together with the pivot lever arrangement without relative movement between these two lever arrangements. Hence, during the first mode of operation, the pivot lever arrangement and the pivot arm arrangement make up a unique assembly, which is rotated as a whole when the impulse delivered from the door edge is below the predetermined threshold value in the first mode of operation. 
     However, in the second mode of operation when the second impulse delivered from the door edge to the pivot arm arrangement is above the predetermined threshold value, the pivot arm arrangement at least partially uncouples from the pivot lever arrangement thereby exposing the first engagement means. As the second engagement means is located at the same path of travel of the door as the engagement means, the second engagement means will engage with the first engagement means when advancing the first engagement means by further movement of the door, whereby the first engagement means will be detached from the pivot arm arrangement at which it was originally attached in a positive manner by means of a ball catch for example. Hence, by still further movement of the door, the belt of the deceleration device will be withdrawn from its spool wheel thereby breaking the acceleration of the door. 
     In other words, the present invention provides an operation mechanism, which is adapted for activating a deceleration device for decelerating an opening movement of the cockpit door, wherein the operation mechanism features a first mode of operation and a second mode of operation. In this connection, the first operation mode is characterized in that it allows free rotation of the cockpit door, when the operation mechanism is loaded by an impulse of the door below a predetermined threshold value. In contrast thereto, the second mode of operation is characterized in that the operation mechanism in the second mode of operation decelerates free rotations of the door by connecting the door to the deceleration device, when the operation mechanism is loaded by an impulse of the door above the predetermined threshold value. 
     Hence, by decelerating free rotation of the door by connecting the door to the deceleration device, the present invention provides an effective means of reducing the end energy of the cockpit door since the free kinetic energy of the door may be abolished by the deceleration device. 
     As will become apparent from the previous remarks, the functioning of the operation mechanism of the present invention depends on the impulse energy delivered from the door edge via the pivot arm arrangement and the pivot lever arrangement to the damping arrangement. When the impulse energy is below a predetermined threshold value, the operation mechanism will be operated in the first mode of operation whereas the second mode of operation will take place when the impulse energy is above the predetermined threshold value. For example, seen from a static angle, the operation mechanism will be operated in the first mode of operation when a static force below 8 daN is applied to the door edge. However, under decompression conditions, the force acting on the door edge may mount to almost 700 daN wherefore the second mode of operation will take place. Hence, talking in terms of static forces the lever should move without the dampers locking in the first mode of operation with an applied load of 8 daN (and a little more for comfort), whereas the transition between normal movement in the first mode of operation and the locking in the second mode of operation should occur at e.g. 10 times normal load. Hence under static conditions the critical force may amount to about 80 daN, for example. 
     As will become apparent from the above illustrations, since the first engagement means will be engaged with the second engagement means, the deceleration device coupled with the operation mechanism will be activated which will dissipate the kinetic energy of the moving door in the second mode of operation during an event of cockpit decompression. Since the deceleration device will dissipate most of the kinetic energy, the end energy of the door at a venting area of 80° or more will be reduced, wherefore the risk of structural or equipment damage or injury to the crew will be avoided or at least be reduced. 
     According to another exemplary embodiment of the present invention, the pivot arm arrangement may be hinged to the pivot lever arrangement comparable to a balance arm, wherein one end of the balance arm is positively connected to the pivot lever arrangement by a ball catch arrangement, for example. Hence, in the first mode of operation, a relative movement between the pivot arm arrangement and the pivot lever arrangement is blocked by a positive locking between these two lever arrangements. In the second mode of operation, when the impulse energy delivered to the pivot arm arrangement is high enough to compensate that positive locking, the pivot arm arrangement carries out a relative movement with respect to the pivot lever arrangement. 
     Although it was illustrated that the pivot arm arrangement in form of a balance arm may be hinged to the pivot lever arrangement being positively locked to the pivot lever arrangement, it may also be possible to positively connect the pivot arm arrangement completely to the pivot lever arrangement without any hinge. In this case, in the second mode of operation when the impulse energy exceeds the predetermined threshold value, the pivot lever arrangement will be completely detached by the advancing door edge, wherein the positive connection between the pivot arm arrangement and the pivot lever arrangement will be compensated. 
     According to a further exemplary embodiment of the present invention, the pivot lever arrangement and the pivot arm arrangement make up a C-shaped configuration, which clasps the door edge of the door in the first mode of operation in a closed door position. In this respect, the pivot arm arrangement in plan view forms a first flange of the C-shaped configuration whereas the pivot lever arrangement in plan view forms the remainder of the C-shaped configuration in form of an L-shaped configuration, i.e. the pivot arm arrangement completes the L-shape to a C-shape. Since the pivot arm arrangement and the pivot lever arrangement rotate without any relative movement in the first mode of operation, the C-shaped configuration will rotate as a whole from a closed position to an open position, thereby allowing the door edge to escape from the clasp of the C-shaped configuration. Hence, when the door is in its closed position, the door edge will be clasped by the C-shaped configuration, whereas this clasping engagement will be released in the first mode of operation due to the rotation of the door and the rotation of the C-shaped configuration resulting from the rotary movement of the door. 
     Since it might be desirable to clasp the door edge again during a closing movement of the door, it is necessary to hold the C-shaped configuration in its open position, as long as the door is open. Therefore, the operation mechanism additionally comprises a spring arrangement, which is adapted to bias the pivot lever arrangement into the closed position or into the open position respectively. To this effect, the spring arrangement is configured to switch between said two biasing modes during rotation of the C-shaped configuration from the closed position to the open position and vice versa, wherefore the spring arrangement is hinged to the pivot lever arrangement in order to snap over a dead centre during movement of the pivot lever arrangement. Due to the switching between said two biasing modes, the spring arrangement will not continuously press the C-shaped configuration in its open position, which would be undesirable, since in this case, even in the closed position of the door, the spring arrangement would try to bias the door open. 
     Although the spring arrangement is adapted to hold the C-shaped configuration in its open and closed position respectively, the locking achieved thereby is only elastic. However, to attain a locking with respect to the C-shaped configuration which is adapted to withstand an accidental movement of the C-shaped configuration, the operation mechanism may additionally comprise a pawl lever arrangement which is configured to lock the pivot lever arrangement in the open position and which is adapted to be unlocked by the door edge during a closing movement of the door. To this effect, the pawl lever arrangement may comprise at least one pawl lever arranged in the track of travel of the door, so that, during a closing movement of the door the pawl lever arrangement is operated by the door thereby unlocking the pawl lever arrangement. 
     In order to generate a blocking force to withstand the impulse energy imparted to the operation mechanism, the damping arrangement may comprise a dashpot damper in the form of a hydraulic piston cylinder unit for example, which goes into a momentary hydraulic lock, when the second impulse delivered from the door edge is above the predetermined threshold value. 
     Since it may desirable that the operation mechanism is not visible from the outside, the operation mechanism may be designed to be partially housed within a doorpost next to the door edge. However, in order to activate the operation mechanism, the doorpost comprises at least two openings through which the pivot arm arrangement and the pivot lever arrangement project into the door&#39;s track of travel respectively. 
     To allow a smooth sliding movement of the door edge with respect to the pivot arm arrangement, the operation mechanism may further comprise a fitting, which is mountable to the door edge and which comprises a roller arrangement, which is adapted to contact and roll along the pivot lever arrangement during the opening movement of the door. 
     In the preceding paragraphs, the operation mechanism was illustrated as comprising several arrangements, in particular a pivot lever arrangement, a pivot arm arrangement, a pawl lever arrangement, a damping arrangement and a roller arrangement. These arrangements may be made up of two corresponding assemblies respectively which are vertically offset to each other. For example, the pivot lever arrangement may comprise two pivot levers, which are spaced vertically apart from each other. The pivot arm arrangement may comprise two pivot arms, which are vertically offset to each other. The same applies to the pawl lever arrangement, the damping arrangement and the roller arrangement respectively which are redundantly designed consisting of two pairs of arrangement components being vertically offset to each other. The redundant provision of components may make it possible that the operation mechanism will still work although one component is out of order. 
     According to another exemplary embodiment of the invention, the operation mechanism comprises a deceleration device which is adapted for gradually dissipating the kinetic energy of a swiveling door, for example, in the event of a cockpit decompression. Inter alia, the deceleration device comprises a spool wheel which is designed to carry a belt which is wound up on the spool reel. The belt of the spool reel is adapted to be automatically connected to the cockpit door in the event of a cockpit decompression in order to absorb some of the kinetic energy of the cockpit door. The deceleration device moreover comprises an elevating spindle which is adapted to be driven by said spool reel in the event that the belt is being retracted from the spool reel. The deceleration device includes at least one collet which is screwed to the elevating spindle so that the collet may move in a longitudinal direction of the elevating spindle due to a rotation of the spool reel. For purposes of dissipating kinetic energy, the deceleration device includes at least one spring assembly which is installed between the collet and a fixed bearing portion of the deceleration device. Hence, the at least one collet will be screwed towards the fixed bearing portion by retraction of the belt from the spool reel whereby the spring assembly will be compressed, so that a reaction load is generated by the spring assembly counteracting the retraction of the belt. 
     Therefore, by means of the deceleration device it is possible to decelerate the acceleration of a cockpit door in the event of a cockpit decompression by generating a reacting force which counteracts the movement of the door. 
     According to another exemplary embodiment of the present invention, the spring assembly comprises a plurality of compression springs which are situated between the collet and the spring bearing portion thereby surrounding the elevating spindle. The provision of a plurality of compression springs may be useful since in the event that a single spring should break down, the deceleration device will remain operative. For example, the plurality of compression springs may coaxially surround the elevating spindle. As an alternative, the plurality of compression springs may be disposed in regular intervals around the elevating spindle. 
     According to a further embodiment of the invention, the collet may be shaped in the form of a polygon in plan view which comprises a plurality of rounded edges which form receptacles for the plurality of compression springs which are disposed at regular intervals around the elevating spindle. 
     To avoid a rotation of the collet due to rotation of the elevating spindle, the deceleration device may further comprise at least one cup-shaped housing comprising a cam profile which matches the polygonal shape of the collet to allow the collet to slide into the housing and to avoid rotation of the collet. In this embodiment, the fixed bearing portion mentioned above forms part of the base of the housing, so that the plurality of compression springs is situated between the base of the cup-shaped housing and the collet. Instead of providing a cup-shaped housing for purposes of guiding the collet in the longitudinal direction of the elevating spindle, it may be possible to provide other guiding means for guiding the collet in longitudinal direction of the elevating spin thereby exclusively avoiding a rotation of the collet with respect to the bearing portion. 
     According to another exemplary embodiment, the elevating spindle comprises a bearing shaft which is rotatably mounted in the fixed bearing portion and a threaded shaft sleeve surrounding the bearing shaft. In this embodiment, the bearing shaft, the bearing sleeve and the spool reel surrounding the elevating spindle are connected to each other by means of a single shear pin. The connection of these three elements by means of a single shear pin may be useful, since in case that the total travel of the collet along the elevating spindle should be exploited, further rotation of the spool reel will not damage the elevating spindle as a whole. Rather, the shear pin will be sheared off whereby it is possible that only the shaft sleeve will be damaged and the bearing shaft will remain intact. Moreover, the provision of a single shear pin may be useful since in case that the total travel of the collet along the elevating spindle should be exploited, further kinetic energy will be dissipated by shearing the shear pin. 
     To provide a further means for dissipating kinetic energy in the event that the total travel of the collet along the elevating shaft should be exploited, the deceleration device may further comprise at least one energy-absorbing tube surrounding the elevating spindle which is arranged to come prior into contact with the fixed bearing portion than the at least one collet to dissipate further energy by deformation of the at least one energy absorbing tube. For example, the energy absorbing tube may be connected to the collet surrounding the elevating spindle. 
     According to yet another exemplary embodiment, the deceleration device may comprise a plurality of wave spring washers, which have a negligible spring constant. In this connection, the plurality of spring washers is connected in series with the plurality of compression springs, so that during an initial rotation of the spool reel no reaction load will be generated due to the negligible spring constant of the plurality of spring washers. 
     The provision of the spring washers may be useful since it may be advantageous to allow the door to open and initially accelerate as quickly as possible during a first opening angle so that in case of a cockpit decompression the pressure load across the door will not adversely increase. 
     According to a final exemplary embodiment of the present invention, the whole deceleration device is symmetrically and redundantly designed. In this connection, the deceleration device comprises an elevating spindle which features right-hand and left-hand threads at either side of a central portion which is surrounded by the spool reel. Due to a retraction force, the spool reel screws a first collet toward a first fixed bearing portion, thereby compressing a first spring assembly situated between the first collet and the first fixed bearing portion. In comparison, due to the retraction force, the spool reel screws a second collet toward a second fixed bearing portion, thereby compressing a second spring assembly situated between the first collet and the first fixed bearing portion. 
     According to a yet another exemplary embodiment of the present invention, a cockpit door arrangement for use in an aircraft is provided which comprises a cockpit door as well as an operation mechanism as is illustrated in the preceding paragraphs and which is arranged for activating a deceleration device for decelerating an opening movement of the cockpit door in the event of a cockpit decompression. 
     Finally, it is suggested to use an operation mechanism as illustrated in the preceding paragraphs aboard an aircraft, which is arranged for activating a deceleration device for decelerating an opening movement of a cockpit door in the event of a cockpit decompression. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, the present invention will be illustrated with reference to the drawings enclosed herewith. 
       In the drawings: 
         FIG. 1  shows a diagram illustrating pressure versus energy over door angle; 
         FIG. 2 to 5  show a plan view onto the operation mechanism of the present invention during a door opening movement in the first mode of operation; 
         FIGS. 6 and 7  show a plan view onto the operation mechanism of the present invention during a closing movement of the door in the first mode of operation; 
         FIG. 8  illustrates the functionality of the pawl lever arrangement; 
         FIG. 9  shows another plan view onto the operation mechanism of the present invention in a closed door position; 
         FIG. 10 to 13  show cross-sectional views through the operation mechanism during an opening movement of the door in the second mode of operation; 
         FIG. 14  illustrates the section line to receive  FIG. 14 ; 
         FIG. 15  shows a sectional view through the operation mechanism including the deceleration device along line A-A in  FIG. 14   
         FIG. 16  shows a diagram illustrating the effect of the deceleration device with respect to the door energy; 
         FIG. 17  shows a diagram illustrating the effect of the deceleration device with respect to the door opening time; and 
         FIG. 18  shows a diagram illustrating the effect of the deceleration device with respect to the differential pressure. 
     
    
    
     In the following description of the figures, the same reference characters are used for identical or similar elements. 
     DETAILED DESCRIPTION 
     The following paragraphs detail the operation mechanism  1 , which is mounted in the doorpost  26  next to the door edge  4  of the cockpit door  3 . The doorpost  26  is covered by a sprung loaded protective sheath  25  to provide effective means with respect to external demolitions. The operation mechanism  1  employs a deceleration device  2  comprising a rated belt  19 , which is similar in material and construction to a seat or cargo harness. The deceleration device  2  is dormant in the first mode of operation of the operation mechanism  1  and is activated by the high forces generated in a decompression to attach the belt  19  to the door  3  via a buckle  20  and a catch arrangement in form of a hook  21 . 
     In normal use, the operation mechanism  1  is rotated open and close with the movement of the door  3 , without impeding entry or exit. 
     As will become apparent from  FIGS. 2 to 5 , the operation mechanism  1  comprises a pivot lever  5  that carries a buckle  20  to which the belt  19  of the deceleration device  2  is positively attached as is shown in  FIGS. 10 to 13 . Pivot lever  5  is rotatably mounted to swivel around axis  27 . A fitting  17  is located on the door edge  4  comprising a roller  18  and a hook  21 , which is located in the plane of buckle  20 . During the opening movement of the door  3 , the roller  18  of fitting  17  will contact the pivot arm  6 , rotating it away from the advancing door. Since pivot arm  6  is connected to pivot lever  5 , rotation of pivot arm  6  will be transferred to pivot lever  5 , which is controlled by dashpot damper  7  and compression spring  12 . Hence, in the first mode of operation, pivot lever  5  will turn around axis  27 . 
     Pivot lever  5  will be kept open by use of a pawl lock arrangement  13 ,  14 ,  16  which is spring loaded and unlocked by advancement of the door  3  to the closed position, ensuring that the door  3  may be safely closed without being prevented by the pivot lever  5 . 
     In the following, the operation mechanism will be illustrated in detail with reference to the drawings. As will become apparent from  FIG. 2 , the operation mechanism is substantially completely housed within doorpost  26  next to the door edge  4  of door  3 . The operation mechanism  1  comprises at least a pivot lever arrangement of two pivot levers  5 , and a pivot arm arrangement of two pivot arms  6 , which are vertically offset from each other as will become apparent from  FIG. 15 . Pivot arm  6  is located in the track of travel of the door edge  4  and is coupled to the pivot lever  5  by hinge pin  10 . Moreover, pivot arm  6  is coupled to pivot lever  5  by a ball catch arrangement  11 , which will unlock when the impulse energy delivered by door edge  4  exceeds a predetermined threshold value. Pivot lever  5  is rotatably mounted to swivel around axis  27 . 
     Furthermore, the operation mechanism  1  comprises a damping arrangement comprising two dashpot dampers  7  which are vertically offset as is depicted in  FIG. 15 . The dashpot damper  7  rests against a post on pivot lever  5  and is connected to a fixed position of the operation mechanism  1 . 
     As will become apparent from the drawings, the pivot lever  5  and the pivot arm  6  make up a C-shaped configuration clasping the door edge  4  in the first mode of operation as is depicted for example in  FIG. 2 . In this respect, the pivot arm  6  forms a flange of the C-shaped configuration and the pivot lever  5  forms the reminder of the C-shaped configuration in form of an L-shaped configuration. 
     A pawl lever arrangement is located and mounted at the bending region of the L-shaped pivot lever  5  and comprises an arcuate pawl lever  13  rotatably mounted around axis  27  on pivot lever  5 . Pawl lever  13  is spring loaded in order to carry out a clockwise rotation. An escape wheel  14  is connected to pivot lever  5  aligned with axis  27  and is adapted to engage with escape wheel lever  16  which is rotatably mounted to a fixed position of the operation mechanism  1 . Escape wheel lever  16  is spring loaded in order to carry out a rotation in counter clockwise direction. The pawl lever  13  comprises a cam profile  15 , which is adapted to interact with escape wheel lever  16  for purposes of disengaging escape wheel lever  16  from escape wheel  14 . 
     The operation mechanism  1  furthermore comprises a spring arrangement comprising two compression springs  12 , wherein each compression spring  12  is hinged at one end to a fixed position of operation mechanism  1 . At the other end, the compression spring  12  is connected to the bent region of the L-shaped pivot lever  5 , wherein the longitudinal axis of compression spring  12  is not aligned with axis  27 . Since pivot lever  5  is rotatably mounted with respect to axis  27 , spring  12  is adapted to bias the pivot lever  5  either into the closed position of  FIG. 2  or into an open position as is shown in  FIG. 5  for example. 
     As will become apparent from  FIG. 2 , door  3  is in its closed position, wherein door edge  4  is clasped by the C-shaped configuration of pivot lever  5  and pivot arm  6 . As will become apparent from  FIG. 3 , during an opening movement of door  4 , roller  18  contacts pivot arm  5 , wherefore the C-shaped configuration of pivot lever  5  and pivot arm  6  is rotated as a whole around axis  27  due to the impulse energy delivered from door edge  4  to pivot arm  6 . As will become further apparent from  FIG. 3 , pawl lever  13  which is spring loaded around axis  27  imparts a force to fitting  17  via pawl lever roller  28 , wherefore an opening force is generated to allow easy opening of the door which may amount to about 4 to 8 daN. 
     Since the impulse energy delivered from the door edge  4  is below a predetermined threshold value, the positive connection  11  between pivot lever  5  and pivot arm  6  is maintained, wherefore the C-shaped configuration of pivot lever  5  and pivot arm  6  rotates as a whole around axis  27 . Since the energy imparted into pivot lever  5  is below a predetermined threshold, damper  7  will not go into a momentary hydraulic lock wherefore door  3  can be opened without being blocked by damper  7  in the first mode of operation. 
     By the further opening movement of door  3  (cf.  FIG. 4 ), pawl lever  13  rotates in clockwise direction around axis  27 , wherein cam  15  of pawl lever  13  slides along escape wheel lever  16  wherefore escape wheel lever  16  engages with escape wheel  14 , so that the whole operation mechanism  1  will be fixed in the position of  FIG. 4 . 
     As will become apparent from the drawings, doorpost  26  is covered by a rotatable cover  29 , which is rotated due to the rotary movement of the C-shaped configuration of pivot lever  5  and pivot arm  6 . 
       FIGS. 6 and 7  illustrate the disengagement of escape wheel lever  16  from escape wheel  14  during a closing movement of door  3 . When door  3  contacts pawl wheel roller  28 , pawl lever  28  will be rotated in counter-clockwise direction whereby cam  15  contacts escape wheel lever  16  thereby disengaging the escape wheel lever  16  from the escape wheel  14  so that the lock of the pawl lever arrangement is eliminated. Hence, by further closing movement of door  3 , door edge  4  will slide along the free end of pivot lever  5 , wherefore the C-shaped configuration will rotate in counter-clockwise direction against the compression force of spring  12  until spring  12  passes its dead centre so that the C-shaped configuration of pivot lever  5  and pivot arm  6  is biased into its closed position as is depicted in  FIG. 2 . 
     It should be noted that the motion sequence depicted in  FIGS. 2 to 7  illustrate a motion sequence wherein the impulse energy delivered from door edge  4  to pivot arm  6  is below the predetermined threshold value wherefore damper  7  does not go into momentary hydraulic lock. 
     The PTS (Purchaser Technical Specification) for the cockpit door  3  defines an predeterminable opening force to allow easy opening of the door, to prevent noise to the adjacent flight crew rest compartments and to prevent the door from rotating forward when electrical power is removed so that the door locks are unlocked. 
     It should be further noted that as the door  3  is opened, the roller  18  of fitting  17  contacts the pivot arm  6  rotating it away from the door  3  and changing the relationship between the pivot lever  5  and the compression spring  12 . In the closed position, the pivot lever  6  is held by both the door  3  and the compression spring  12 . On opening the door, the relationship changes and the spring  12  adds to rotate pivot lever  5 . Both of these actions decrease the force required to rotate the pivot lever  5  and provide a method of rotating the pivot arm  6  away from the tip of the door edge  4  to ensure adequate clearance when closing. 
       FIGS. 8.1  and  8 . 2  again illustrate the motion sequence of the pawl lever arrangement  13 ,  14 ,  16 . As may be seen from  FIG. 8.1  which shows the pawl lever arrangement in its initial state in pawl lever  13  is tensioned against its tension spring operable around its hinge axis  27 . In this initial state, the pawl lever arrangement is disengaged since escape wheel lever  16  is disengaged from escape wheel  14  (not shown) by means of cam profile  15  of pawl lever  13 . When pawl lever  13  rotates in clockwise direction as is illustrated in  FIG. 8.2 , escape wheel lever  16  falls into lock with escape wheel  14  (not shown) since cam profile  15  no longer blocks the rotary movement of escape wheel lever  16  which is caused due to a torque generated around the pivot axis of escape wheel lever  16  by means of a torsion spring (not shown). 
     In the following, the activation of the deceleration device  2  will be illustrated with reference to  FIGS. 9 to 13 .  FIG. 9  differs from  FIG. 10  only in that in  FIG. 10  the deceleration device  2  as well as the buckle  20  connected to the belt  19  of the deceleration device  2  may be seen more clearly. As will become apparent from  FIGS. 9 ,  10  and in particular  FIG. 15 , the deceleration device is arranged between the elements of the operation mechanism  1  which are all vertically offset in pairs with respect to each other thereby housing the deceleration device  2 . The deceleration device  2  comprises a spring-loaded belt  19  which is connected to a buckle  20  which is concealed by the pivot arm(s) as is depicted in  FIG. 10 . Buckle  20  for its part is detachably mounted between the two vertically offset pivot arms  6  by means of two ball catches  30 . 
     When the impulse energy delivered from door edge  4  to pivot arm  6  is above the predetermined threshold value in the second mode of operation, which is depicted in the motion sequence of  FIGS. 10 to 13 , pivot lever  5  will not rotate since in the second mode of operation the damping arrangement blocks rotation of the pivot lever  5 . Since pivot lever  5  will rest in its initial position when the impulse energy delivered from the door edge  4  to the pivot arm  6  is above the predetermined threshold value, the pivot arm  6  will uncouple from the pivot lever  5  by disengaging the positive fit of ball catch  11  acting between pivot lever  5  and pivot arm  6 . Therefore, due to the impulse energy delivered from door edge  4  to pivot arm  6 , the pivot arm  6  will rotate about hinge pin  10 , thereby exposing the buckle  20  as is illustrated in  FIG. 11 . 
     By further opening movement of the door  3 , the advancing hook  21  provided on fitting  17  engages with recess  8  formed in buckle  20  wherefore due to the tension force imparted from hook  21  to the buckle, the buckle will be detached from the pivot arm arrangement  6  by disengaging ball catch  30  acting between pivot arm  6  and buckle  20  as is depicted in  FIG. 13 . Hence, by further movement of the door  3 , the belt  19  of the deceleration device  2  will be withdrawn from its spool wheel thereby breaking the acceleration of the door  3  by generating a reaction load to the door edge  4  due to the spring operated deceleration device  2 . 
     Recapitulating, it shall become apparent that in the second mode of operation the movement of the pivot levers  5  is controlled and in particular blocked by use of the two linear dashpot type dampers  7 . These dampers  7  allow movement at relatively low loads but under high forces and rapid movements in case of a decompression are forced into a hydraulic lock and hence block the rotation of the pivot lever  5 . In this condition, the pivot arm  6 , which is attached and locked to the pivot lever arrangement  5  by two ball catches  11 , snaps out of engagement with these ball catches  11  and rotates independently. This action will expose the belt buckle  20  which is cradled by the pivot arm arrangement  6 . As the pivot arm arrangement  6  rotates open due to an impulse energy delivered from door edge  4 , the buckle  20  by geometrical definition is retained in the door plane and receives the advancing hook  21  of the door fitting  17 . Further movement of the door engages the hook  21  into the buckle  20  and begins to withdraw the belt  19  from the spool wheel of the deceleration device  2 . 
     Under rotation the spool wheel breaks the acceleration of the door  3  by reacting a small load through an internal mechanism as is depicted in  FIG. 15 . Thus, the reaction force is realised. 
     The following paragraphs detail the deceleration device  2 , which is mounted within doorpost  15 . As will become apparent from  FIG. 2 , the deceleration device  2  comprises a housing  7  in which the main components of the device  2  are installed. In particular, an elevating spindle  16  extends in a vertical direction and rotates in two bearings  14  which are supported on housing  7 . The elevating spindle  16  may consist of two mating parts, a bearing shaft  11  and a shaft sleeve  12  featuring both right hand and left hand threads either side of a short central plain shank  17 . 
     The deceleration device  2  moreover comprises a spool reel  4  which surrounds the plain shank  17  of the elevating spindle  17 . A belt  3  is wound up on the spool reel  4  and is connected to a buckle  5  which is positively held in position by means of two ball catches  6 . The shaft assembly  11 ,  12  slides into the spool reel  4  and is locked to the spool reel  4  by means of a single shear pin  8 . At either end the shaft is supported by the plain bearings  14  which are in turn supported to the main housing  7 . 
     On each side of the spool reel  4 , steel collets  10  screw down the threads of the shaft sleeve  12 . The collets  10  may be profile milled to a rounded hexagonal shape and fit within a matching profile of the housing  7 . Between collet  10  and housing  7  six compression springs are installed on either side of the plain shank  17  in recessed pockets in both collet and housing, such that they are held in position by the collets  10  and the housing  7 . 
     When the first engagement means  8  of the operation mechanism in the second mode of operation is engaged with the second engagement means  9  of the operation mechanism  1 , the belt  3  from the spool reel  4  will be retracted causing the spool reel  4  to rotate. This rotation will be directly transferred (via the shear pin) to the shaft assembly. As each of the collet  10  is captivated by its conforming profile in its respective housing  7 , the rotational movement of the spool reel  4  and shaft assembly  11 ,  12  is transferred to the linear movement of the collets  10 . The movement of the collets  10  is outwards from the spool reel  4  in the direction of the housing  7  such that the captivated springs are compressed along their free length. Thus for each 360° of rotation 1.5 mm of linear travel (standard 10.0 mm metric thread=1.5 mm pitch) may be achieved. The collective spring force is set to react to a load such that a predetermined force is required to extract the belt  3  from the spool reel  4 . For example, the springs  9  might be designed to have a constant spring rate such that the force remains constant through the angular rotation of the spool  4 . However as the belt  19  retracts from the spool  4  the diameter of the belt on spool reel  4  decreases. Hence, each successive rotation requires less length of belt due to the geometry of the belt on the spool reel  4 . So by virtue of the belt geometry the reaction force to the door movement may be described as progressive. 
     The first rotation of the spool reel  4  does not compress the springs  9  but brings both collets  10  into engagement. This is to allow a single free rotation of the spool reel  4  with minimal force. To this effect, a plurality of wave spring washers  18  having a negligible spring constant may be connected in series with the plurality of compression springs  9 , so that during an initial rotation of the spool reel  4  no reaction load will be generated due to the negligible spring constant of the plurality of wave spring washers  18 . The first complete rotation may be equivalent to the door opening by approximately 10° (belt extracted by 150 mm). This first free movement is intended to allow the door  3  to open and initially to accelerate as quickly as possible so as not to adversely increase the pressure load across the door  3  and is timed to a point where the pressure load peaks and begins to fall whereas the door energy overtakes the peak pressure load and begins to accelerate rapidly (cf.  FIG. 1 ). 
     Additionally, where maintenance inspection or unit failure or accidental engagement of the belt  3  occurs during normal use, the first free rotation allows the door to open sufficient to allow detachment of the belt from the cabin side. The belt is self retracting by means of a drive spring situated at one end of the shaft assembly. The drive spring is set to retract the belt by one revolution, it is connected to the shaft by means of a sprung loaded gear that will slip freely on the shaft if rotation exceeds one revolution. 
     The total travel of the collet  10  along the shaft assembly may be 10.5 mm which translates to 7 full turns (760 mm of belt extension). This allows the door to rotate through to its maximum venting area at 80°. 
     Prior to reaching the end stop a further method of energy absorption may be employed by incorporating an energy absorbing tube  13  into the end of the collets  10  such that the collets  10  contact the housing  7  before the maximum travel of 10.5 mm. Hence, the force which is necessary to collapse the energy absorbing tube  13  is dissipated due to the deformation of the energy absorbing tube  13 . 
     Finally, further kinetic energy may be absorbed from the travelling door  3  at an angle close to its maximum vent area due to the two part design of the elevating spindle  16 . The shaft assembly  11 ,  12  is designed as two parts to allow shearing of the threaded sleeve  12  from the spool reel  4  without affecting the structural integrity of the main support bearing shaft  11 . Hence, due to the relative movement of threaded sleeve  12  from the spool reel  4  shearing the single shear pin  9 , further kinetic energy may be absorbed. 
     The intention is to absorb the maximum energy from the travelling door throughout its rotation from 10° onwards, without adversely increasing the pressure load, whilst limiting the maximum reaction load. 
     In the following, the effect of the operation mechanism on the door will be illustrated. It can be seen from the following graph of  FIG. 16  that reacting a force (normal to door plane) at the door centre of area by means of the deceleration device  2  throughout the doors rotation under decompression load will reduce the end energy. In particular:
         Reacting a load of 50 daN at the door centre of area will reduce the end energy by 8% (2684 J to 2473 J).   Reacting a load of 100 daN at the door centre of area will reduce the end energy by 16% (2684 J to 2263 J).   Reacting a load of 150 daN at the door centre of area will reduce the end energy by 24% (2684 J to 2054 J).   Reacting a load of 200 daN at the door centre of area will reduce the end energy by 32% (2684 J to 1840 J).   Reacting a load of 250 daN at the door centre of area will reduce the end energy by 40% (2684 J to 1630 J).       

     Assuming a series of reaction loads as described in the foregoing paragraph, the effect of door opening time is shown in  FIG. 17 . As will become apparent from  FIG. 17 ,
         Reacting a load of 50 daN at the door centre of area increases the time taken to reach the minimum venting area (80°) by 3% (0.067 ms to 0.069 ms);   Reacting a load of 100 daN at the door centre of area increases the time taken to reach the minimum venting area (80°) by 4.5% (0.067 ms to 0.070 ms);   Reacting a load of 150 daN at the door centre of area increases the time taken to reach the minimum venting area (80°) by 7.5% (0.067 ms to 0.072 ms);   Reacting a load of 200 daN at the door centre of area increases the time taken to reach the minimum venting area (80°) by 10.5% (0.067 ms to 0.074 ms);   Reacting a load of 250 daN at the door centre of area increases the time taken to reach the minimum venting area (80°) by 13% (0.067 ms to 0.076 ms).       

     Assuming a series of reaction loads as described above, the effect on the cockpit wall pressure difference is shown in  FIG. 18 , which shows that
         Reacting a load of 50 daN at the door centre of area increases the differential pressure by 0.67% (119 hPa to 119.8 hPa);   Reacting a load of 100 daN at the door centre of area increases the differential pressure by 1.26% (119 hPa to 120.5 hPa);   Reacting a load of 150 daN at the door centre of area increases the differential pressure by 1.85% (119 hPa to 121.2 hPa);   Reacting a load of 200 daN at the door centre of area increases the differential pressure by 2.5% (119 hPa to 122.0 hPa);   Reacting a load of 250 daN at the door centre of area increases the differential pressure by 3.2% (119 hPa to 122.8 hPa).       

     Hence, reacting a load equivalent to 250 daN at the door Centre of Area reduces the end energy by over 1000 Joules (40%) but increases the cockpit wall differential pressure by just 3.8 hPa (3.2%). Thus a method for controlling and reducing the end energy of the door without substantially increasing the pressure load upon the monuments can be realised by means of the present operation mechanism. 
     In addition it should be pointed out that “comprising” does not exclude other elements or steps, and “a” or “one” does not exclude a plural number. Furthermore, it should be pointed out that characteristics or steps which have been described with reference to one of the above embodiments can also be used in combination with other characteristics or steps of other embodiments described above. Reference characters in the claims are not to be interpreted as limitations. 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. 
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 REFERENCE LIST 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 operation mechanism 
               
               
                 2 
                 deceleration device 
               
               
                 3 
                 door 
               
               
                 4 
                 door edge 
               
               
                 5 
                 pivot lever 
               
               
                 6 
                 pivot arm 
               
               
                 7 
                 damping arrangement 
               
               
                 8 
                 first engagement 
               
               
                   
                 means 
               
               
                 9 
                 second engagement 
               
               
                   
                 means 
               
               
                 10 
                 hinge pin 
               
               
                 11 
                 ball catch 
               
               
                 12 
                 compression spring 
               
               
                 13 
                 pawl lever 
               
               
                 14 
                 escape wheel 
               
               
                 15 
                 cam 
               
               
                 16 
                 escape wheel lever 
               
               
                 17 
                 fitting 
               
               
                 18 
                 roller 
               
               
                 19 
                 belt 
               
               
                 20 
                 buckle 
               
               
                 21 
                 hook 
               
               
                 22 
                 recess 
               
               
                 25 
                 protective sheath 
               
               
                 26 
                 doorpost 
               
               
                 27 
                 axis of 5 and 13 
               
               
                 28 
                 pawl lever roller 
               
               
                 29 
                 cover 
               
               
                 30 
                 ball catch (buckle) 
               
               
                 104 
                 spool reel 
               
               
                 107 
                 housing 
               
               
                 108 
                 shear pin 
               
               
                 109 
                 spring 
               
               
                 110 
                 collet 
               
               
                 111 
                 bearing shaft 
               
               
                 112 
                 Shaft sleeve 
               
               
                 113 
                 energy absorbing tube 
               
               
                 114 
                 bearing 
               
               
                 115 
                 elevating spindle 
               
               
                 116 
                 plain shank 
               
               
                 117 
                 wave spring washer