Abstract:
A door latch mechanism mounted in a door frame cooperates with a door bolt separating the cockpit compartment on an aircraft from the passenger compartment. The mechanism prevents a hijacker from entering the cockpit compartment and allows the door to open rapidly when a catastrophic decompression event occurs in the airplane.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This application relates to locking mechanisms for doors, particularly doors used to separate an aircraft cockpit compartment from an aircraft passenger compartment. 
   2. Description of the Related Art 
   In a commercial airliner, a door is typically provided between the cockpit and the passenger area. This is desirable for a number of reasons. The door can be locked with a lock typically being controlled by the crew in the cockpit, such as an electrically operated lock. The door gives the crew in the cockpit a measure of security from disturbances in the passenger area. Also, it isolates the crew from the noise in the passenger area, which is desirable to prevent fatigue and to facilitate concentration. Also, with the cockpit sealed, the air conditioning in the cockpit can be handled in a manner different from the passenger area. This is advantageous for crew performance. 
   At the same time, it is necessary that the pressure differential between the cockpit and the passenger area not exceed a certain level in that a decompression condition in either area can cause serious structural damage to the airplane. Currently, this goal is accomplished by having a door locking mechanism give way when the door is subjected to a certain force, such as about 160 pounds. Unfortunately, a hijacker can fairly readily manually produce sufficient force to open the door in that fashion. Consequently, a need exists for a system that will provide the necessary privacy, prevent decompression damage, and at the same time provide the necessary security to prevent a hijacker from entering the cockpit. It is, of course, necessary that the system be practical and reliable. 
   SUMMARY OF THE INVENTION 
   In accordance with the invention, an aircraft door is provided with a strong locking mechanism that cannot be broken simply by manual force. The lock is controlled either by a crew member within the cockpit or a pressure sensor. The pressure sensor prevents damage to the aircraft if a decompression situation should occur in the cockpit. Decompression in the passenger area is not a concern since the amount of in-rushing air from the cockpit is small in comparison with passenger area volume. 
   A spring loaded catch cooperates with the door bolt or latch to hold the door closed. In the event a hijacker attempts to enter the cockpit compartment by applying a load on the door and locking mechanism, a pin supports the load on the door catch and prevents the hijacker from breaking connection between the door latch and the catch. 
   While the pin is able to withstand a force well over that which hijackers could apply, the pin can be quickly retracted from its supporting position to allow the door to overcome the spring force and swing open when a decompression event occurs in the cabin of the plane. The pin is retracted when the pressure sensor sends a signal to an actuator such as solenoid linked to the pin. 
   The attached drawings illustrate a concept for such a mechanism. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a front view of the preferred embodiment of the locking mechanism of the invention. 
       FIG. 2  shows a back view of the mechanism. 
       FIG. 3  shows a right side view of the mechanism. 
       FIG. 4  shows a left side view of the mechanism. 
       FIG. 5  shows a perspective view of the mechanism linked to a schematically illustrated pressure sensor and control circuit. 
       FIG. 6  shows an enlargement of the view in  FIG. 5  without the support housing. 
       FIG. 7  schematically shows a locking pin of the mechanism in an extended position. 
       FIG. 8  shows the locking pin in a retracted position. 
       FIG. 9  is an end view of the locking mechanism with the main support removed and with the catch engaging a latch on a door. 
       FIG. 10  is the same as  FIG. 9  with a portion of the catch broken away to see the roller carried by the catch. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIGS. 5 and 6 , the latch mechanism of the invention includes a strike or catch  10 , a pin  12 , a pair of rollers  14  and  16  mounted on pins  18 , and an actuator such as a solenoid  20 , all supported on a housing or support  22 . The solenoid is controlled by a schematically illustrated pressure sensor  24  and a control circuit  25 . The latch mechanism is normally positioned vertically on a door frame aligned to allow a door bolt or latch to engage the catch  10  when a door is swung into a closed position. 
   As seen in  FIGS. 5 and 6 , the catch  10  is pivotally mounted on a pin  30  mounted on the support  22  and held in a normally door closed position by the urging of a biasing element such as a spring  32 . The catch  10  is shown in  FIG. 9  engaging a door latch or bolt  40  to hold a door  42  in a closed position. If, however, a force is applied against the door that exceeds the spring force, the catch  10  is rotated about the pin  30  to an unlatched position allowing the door to swing open. A door knob may be provided on the pilot compartment side to retract the latch  40  to open the door in conventional fashion. 
   Referring to  FIGS. 6-10 , the latch mechanism is reinforced with the pin  12 , which is connected to the solenoid  20  to prevent unintended individuals, who exert a load on the door, from entering the cockpit. If such an individual tries to force the door open by overcoming the biasing spring  32 , the catch  10  is maintained in the normal position by the pin  12  which is restrained by the roller  14  which is supported by the housing  22 . Unlike the spring  32 , the pin  12  backed by the support  22  can withstand a load greater than that which an intruder could manually produce. 
   As important as it is in preventing individuals from compromising the security of the occupants in the cockpit, the pin  12  would prevent the door from swinging open during a decompression event. Thus, the pin  12  must be quickly removed during such a catastrophic event. This is achieved by the cooperation of the pin  12 , the solenoid  20 , and the pressure sensor  24 , and control circuit  25 . The pressure sensor detects a significant change or rate of change in air pressure in the cockpit. When a dramatic change in air pressure occurs, the sensor deactivates the solenoid  20  which retracts the pin  12  away from its extended position, as shown in  FIG. 7 , to a retracted position shown in FIG.  8 . When the pin  12  is fully retracted, the only force holding the door in the closed position is the biasing spring  32 . However, because the pressure sensor will only send a signal to the solenoid  20  when the change in the cockpit air pressure is significant, the large load on the door will overcome the spring force and swing the door away from its closed position to equalize the air pressure between the cockpit and passenger cabin. 
   To aid with the retraction of the pin  12 , the solenoid  20 , which is commercially available, has two opposing springs for quick response. One spring urges the solenoid rod into its normal position in which the solenoid coil is not energized and the other spring provides force to assist the electrical force on the rod when the solenoid is energized. One suitable solenoid of this type is available from Moog, Inc., in Salt Lake City, Utah. In addition, the hole  44  for the pin in the support  22  is oversized so that friction is reduced or eliminated between the pin  12  and the hole when the pin extends into and retracts from the support. Preferably, the hole is sized so that the pin  12  does not come in contact with the support. Rather, the pin  12  floats through the hole  44  in the support  22  and is guided only by the rollers  14  and  16 . The pin  18  for the roller  14  is mounted in the support  22  while the pin for the other roller  16  is mounted to the catch  10 . 
   While the rollers  14  and  16  help maintain the proper position of the pin  12  even when a load, roughly perpendicular to the pin  12 , is applied, they also provide the added advantage of reducing drag on the pin  12  when it rapidly retracts from its extended position. When the pin  12  is caused to retract, the rollers  14  and  16 , by riding along the tapered tip of the pin  12 , work to push the pin  12  away. In addition, when the tip of the pin passes the centerline  13  of the rollers, the roller  16  will push the pin away from the swing path of the catch  10 . 
   The angle α of the slope on the tip of the pin  12  is preferably between 4 to 6 degrees for the purpose of assisting with the decompression event. However, one of ordinary skill in the art can appreciate that the angle α can be modified. The angle α is dependent on the size of the rollers  14  and  16  and their respective pivot pins  18 , as well as the friction coefficient and holding force of the solenoid  20 . 
   Based on decompression testing using the preferred embodiment, having a pin  12  design with sloped sides of 4 to 6 degrees, the door should be fully free to move within 4 to 12 milliseconds. The response time is dependent on the type of door and bolt. 
   
     
       
             
           
             
             
             
             
             
           
         
             
               TABLE 1 
             
           
           
             
                 
             
             
               Decompression Test Configurations 
             
           
        
         
             
                 
               PSI 
               Mylar Pattern 
               Door 
                 
             
             
               Test 
               Differential 
               (Opening) 
               Configuration 
               Bolt Material 
             
             
                 
             
             
               1 
               2 
               Circular 
               First 
               Nylon 
             
             
               2 
               3 
               Circular 
               First 
               Nylon 
             
             
               3 
               3 
               Square 
               First 
               Nylon 
             
             
               4 
               3 
               Circular 
               Second 
               17-4 55 
             
             
               5 
               3 
               Circular 
               Second 
               17-4 SS 
             
             
                 
             
           
        
       
     
   
   Five separate tests were conducted on the preferred embodiment. As shown in Table 1, each test varied based on the amount of pressure applied, the mylar pattern employed, and the type of door and bolt used. To obtain a decompression event, mylar was burned enough to create a “full aperture.” At that moment, the solenoid was caused to move triggering the pin to retract from supporting the catch. Table 2 provides the test results from the experiment. The results track the amount of time, in milliseconds, it took for: (1) the mylar to burn enough to create a “full aperture” (T FA ); (2) the solenoid to begin moving after full aperture (T SS ); (3) the pin to begin moving after the solenoid began moving (T LSM ); (4) the solenoid to reach full travel after the pin began to move (T FT ); and (5) the door to be free of the pin after the solenoid reached full travel (T DF ). 
   
     
       
             
           
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
           
         
             
               TABLE 2 
             
           
           
             
                 
             
             
               Results from a Decompression Test showing 
             
             
               Elapsed Time in Milliseconds 
             
           
        
         
             
                 
               Test 
               T FA   
               T SS   
               T LSM   
               T FT   
               T DF   
             
             
                 
                 
             
           
        
         
             
                 
               1 
               5.0 
               1.0 
               3.0 
               1.0 
               4.0 
             
             
                 
               2 
               5.0 
               1.0 
               2.0 
               1.0 
               2.0 
             
             
                 
               3 
               6.0 
               0.0 
               4.0 
               1.0 
               7.0 
             
             
                 
               4 
               5.0 
               0.0 
               0.0 
               2.0 
               3.0 
             
             
                 
               5 
               6.0 
               0.0 
               1.0 
               2.0 
               2.0 
             
             
                 
               Average 
               5.4 
               0.4 
               2.0 
               1.4 
               3.6 
             
             
                 
                 
             
             
                 
               T FA  = Time it takes for mylar to burn enough to create a “full aperture” (decompression event)  
             
             
                 
               T SS  = Time when solenoid begins to move after T FA    
             
             
                 
               T LSM  = Time when pin begins to move after T SS    
             
             
                 
               T FT  = Time when solenoid reaches full travel (stroke) after T LSM    
             
             
                 
               T DF  = Time when door is free of strike after T FT    
             
           
        
       
     
   
   Based on the results of the testing, the average time it took after a decompression event for the solenoid to begin moving and triggering the pin was approximately 0.4 milliseconds. From that point, it took approximately 2.0 milliseconds for the pin to begin moving and 3.4 milliseconds for the solenoid to reach full travel. The average time it took for the door to be free of the strike after decompression was approximately 7.4 milliseconds. 
   As one of ordinary skill in the art can appreciate, the preferred embodiment is designed in such a way to respond with sufficient speed to deal with a decompression event. In addition, it is designed to provide the necessary support to maintain a cockpit door in a closed position even when an attempt is made to force the door open by an uninvited individual. 
   Although the foregoing invention has been described in terms of a preferred embodiment, other embodiments will become apparent to those of ordinary skill in the art, in view of the disclosure herein. Accordingly, the present invention is not intended to be limited by the recitation of the preferred embodiment, but is instead intended to be defined by reference to the appended claims.