An access tunnel to an aircraft includes a plurality of tunnel elements each having a longitudinal axis, each tunnel element tapering conically in the direction of the longitudinal axis such that the tunnel elements can be pushed into each other.

CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to European Application Ser. No. EP 15 173 521.4 filed Jun. 24, 2015, which is incorporated herewith in its entirety by reference thereto. 
     FIELD OF THE INVENTION 
     The present invention relates generally to an aircraft tunnel comprising a plurality of tunnel elements which are displaceably connected to each other. 
     BACKGROUND OF THE INVENTION 
     An access tunnel to an aircraft, for example from a parked bus or from a part of a building, is sufficiently known from the prior art. Such access tunnels are used when access to the aircraft should be made possible for passengers from an exit of a building at ground level to the taxiway area without them being exposed to weather conditions. Such access tunnels are known, as already stated. 
     For example, PCT/DE2013/000513 discloses an access tunnel which has a plurality of tunnel elements, whereby the access tunnel can be adapted to the required length. It is known in detail from this citation to displace two elements into one another to protect the individual tunnel elements from contamination, and also from weather effects overall. Provision is made in this respect that a substantially rigid tunnel element as a base element has at least one further tunnel element formed for extension in the manner of a concertina, with the substantially rigid tunnel element as the base element being able to receive the tunnel element formed in the manner of a concertina in it in the manner of a garage. 
     FR 2 886 624 A also discloses an access tunnel to an aircraft which has a plurality of telescopic tunnel elements and two rigid tunnel elements at the end sides which are intended to serve as guide elements on the moving of the access tunnel. The access tunnel described there is thus variable in length. This means that the space requirements of the access tunnel on the airport ramp are variable. 
     An access tunnel to an aircraft is likewise known from WO 01/88274, wherein individual tunnel elements are telescopically connected to one another. It is disadvantageous therein that if a plurality of such tunnel elements are telescopically connected to one another, the clearance width reduces more and more over the length of the tunnel element. This means that the number of the tunnel elements connected in such a manner are absolutely limited. It has furthermore been found to be disadvantageous that, due to the guiding of the individual tunnel elements into one another, a substantial force requirement is necessary to pull the individual elements apart to form the access tunnel. This is because, as already stated, the frameworks of the individual tunnel elements are connected to one another in a guided manner. It would be desirable to overcome the limitations of existing known access tunnels and to provide a better solution. 
     SUMMARY OF THE INVENTION 
     It is an objective of the invention to connect a plurality of tunnel elements to one another such that they can be stored in one another in a space-saving manner without the clearance width reducing as the number of tunnel elements increases. 
     According to one embodiment in accordance with the invention, a plurality of the tunnel elements are formed as tapering conically in the direction of the longitudinal axis of each tunnel element such that the tunnel elements can be pushed into one another. It becomes clear from this that all of the tunnel elements are formed the same, that is each tunnel element has the same respective clearance width at both ends, with each tunnel element, however, having a larger passage width at one end than at the oppositely disposed end. The already previously named conical design of the tunnel elements results from this. This conical design of the tunnel elements, however, has the effect that the individual tunnel elements are displaceable into one another for a space-saving storage in a similar manner to shopping carts. 
     Provision is thus made in accordance with a special feature of the invention that the tunnel elements are freely displaceable relative to one another. This means that the individual tunnel elements are not, for example, connected to one another by guides, but are rather freely movable relative to one another in almost any position. This is also due to the conical design of the tunnel elements. In order now in this connection to prevent the tunnel elements from being pulled apart such that these tunnel elements each stand freely per se, provision is made that the tunnel elements are connected to one another extending in the longitudinal direction by cord, chain, rope, cable or similar to limit the extension. This means that the individual tunnel elements are not guided in one another; they are only connected to one another by the previously described cords, for example, to limit the extension such that the force effort to pull apart the tunnel elements is minimal. 
     The tunnel element comprises a framework on which a cover is arranged, wherein the cover is of arcuate design in its roof. In this connection, the framework has a frame of archway shape at both ends, with the one frame of archway shape being smaller with respect to the circumference than the other frame of archway shape for the conical formation of the tunnel element. A frame of archway shape is understood as one which has two substantially vertically oriented limbs which are connected to one another by an arcuate web in the roof region of the tunnel element so that the frame of archway shape is formed in substantially U shape when viewed. 
     To prevent water from penetrating into the interior of the access tunnel formed by the tunnel elements in the pulled-apart state of the tunnel elements and in the associated radial spacing due to the conical design of the tunnel elements, the frame of archway shape which is larger in circumference has a seal of corresponding archway shape with respect to the adjacent tunnel element. The seal of archway shape is of a flexible design to ensure the leak tightness by the seal on the pushing together of the tunnel elements or on their pulling apart. In accordance with a special feature, provision is made in this connection that the seal of archway shape is elastic at least in the roof region of the tunnel element. Elastic is understood such that the seal is designed in a similar manner to an elastic band in the roof region. Provision is advantageously furthermore made in this connection that the elastic seal of archway shape lies under strain on the cover of the adjacent tunnel element in the roof region of the tunnel element to ensure a very high degree of leak tightness with respect to penetrating moisture. The seal in the region of the limbs of the frame of archway shape is in this respect only flexible in the manner of a cloth which prevents water entering between the vertical side surfaces of two adjacent tunnel elements in driving rain. 
     A seal has been found to be particularly durable which has a reinforcement material coated with an elastomer at at least one side; this means that the seal of archway shape comprises, e.g. in the manner of plastic tarpaulin, a fabric coated with an elastomer. Provision is furthermore made in accordance with a special feature of the invention that the frame of archway shape which is smaller in circumference has two essentially vertically extending limbs at which a respective guidance device for persons proceeding through the access tunnel is arranged. It has already been pointed out at another passage that the tunnel elements are conical, with each tunnel element having a larger frame of archway shape at a front end than at the oppositely disposed end. This means that when the tunnel elements are pulled apart to form an access tunnel, there is a radial spacing between the inner smaller frame of archway shape and the outer larger frame of archway shape of the adjacent tunnel element. To prevent passengers in a crowd from running against the smaller frame of archway shape of the one tunnel element at the front, a respective guidance device is arranged at the essentially vertically extending limbs. Such a guidance device is advantageously designed as a wing pivotable about a vertical axis, that is the wing is arranged in a manner similar to a swing door at the frame of archway shape which is smaller in circumference. The wing is under the load of a spring which provides that the wing is urged in the direction of the frame of the adjacent tunnel element. The pivotable wing advantageously extends approximately over the length or over the height of the limb of the frame of archway shape to save the passengers using the access tunnel from colliding with the frame of archway shape. 
     Provision is furthermore made that the radial spacing between the smaller and the larger frames of archway shape of two tunnel elements is such that, in the substantially pulled apart state of two tunnel elements, the latter can stand at an angle with respect to one another. This means that the circumference of the two frames of archway shape of the tunnel elements is by all means significantly different since the tunnel elements can thereby only be displaced at an angle with respect to one another to allow a flexible shape of the access tunnel overall. 
     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
         FIG. 1  shows an access tunnel with a plurality of elements in the pulled-apart state in a perspective representation; 
         FIG. 1 a    shows the access tunnel of  FIG. 1  in a curved state in the reverse order of the tunnel elements; 
         FIG. 2  shows a representation of  FIG. 1 , with the tunnel elements being pushed into one another; 
         FIG. 3  shows two tunnel elements, with wings as guiding devices being visible through an opening; 
         FIG. 4  shows a section in accordance with the line IV-IV of  FIG. 3 ; 
         FIG. 5  shows a top view of two tunnel elements in the pulled-apart state; and 
         FIG. 6  shows a horizontal section in a view from above. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An access tunnel  1  having a total of four tunnel elements  10  results from  FIG. 1 . Each tunnel element  10  has a framework  12  having four rollers  11 , wherein the framework  12  has a smaller frame  14  of archway shape at one end and a frame  16  of archway shape which is larger in comparison therewith at the opposite end. The term “smaller frame of archway shape” is to be understood in this respect in relation to the term “larger frame of archway shape”; that is, the smaller frame of archway shape has a smaller circumference than the frame  16  of archway shape larger in relation thereto such that a conical extent of the individual tunnel elements  10  results in the longitudinal direction, as is shown in  FIG. 1 . The cornering of an access tunnel  1  having a plurality of tunnel elements  10  is shown in  FIG. 1 a   . The framework marked by  12  has a cover  18 , for example composed of a transparent plastic, over its circumference. 
     The individual tunnel elements  10  are connected to one another by cords  5  to limit the extension of the tunnel elements among one another. Such a cord is located at each side of the tunnel elements. The fastening of the cords  5  takes place between the vertical limbs  14   a  and  16   a  of the frames  14  and  16  of archway shape (see also  FIG. 3 ). The two limbs  14   a ,  16   a  of each frame  14 ,  16  of archway shape are connected to one another by a respective arcuate web  14   b ,  16   b  in the roof region. The frame  16  of archway shape which is larger in relation to the smaller frame  14  of archway shape has a seal  20  likewise of archway shape for bridging the spacing between two tunnel elements  10  in the pulled-apart state of these tunnel elements (see  FIG. 3 ). The seal  20  of archway shape is marked by  22  in the region of the limbs  16   a  of the larger frame  16  of archway shape and contacts the cover of the respective adjacent tunnel element  10  ( FIG. 4 ). The seal  20  of archway shape comprises a reinforcement carrier, for example a fabric, which is coated by an elastomer at at least one side. This cloth is easily deformable and, as already stated, lies at the cover of the adjacent tunnel element  10 . 
     The seal  20  of archway shape in the roof region (arrow  23 ) is elastic per se, that is, is formed in the manner of an elastic band, whereby it is achieved that the seal  20  of archway shape lies under strain on the cover  18  of the adjacent tunnel element in the roof region. This is against the background that in particular no water should be able to enter into the transition region of two tunnel elements in the roof region. 
     If now  FIG. 3  is again looked at, the wings  24  can be recognized at the vertical limbs  14   a  of the frame  14  of archway shape which is smaller in relation to the frame  16  of archway shape, the wings being formed as a guide device and being arranged at the limbs  14   a  pivotable about a vertical axis. The joints of the wings for the connection to the limbs  14   a  are designed in this respect such that the wings  24  come to rest in any predefined position. These wings  24  serve as a guide device or passengers passing through the access tunnel to avoid any collision of the passengers with the frame  14  of archway shape. 
     LIST OF REFERENCE NUMBERS 
     
         
         
           
               1  access tunnel 
               5  cords 
               10  tunnel element 
               11  rollers 
               12  framework 
               14  frame 
               14   a  limb 
               14   b  web 
               16  frame 
               16   a  limb 
               16   b  web 
               18  cover 
               20  seal 
               22  seal, limb 
               23  seal, roof (arrow) 
               24  wing