FIELD 
     The present invention pertains to the configuration of a wheelchair accessible lavatory in an aircraft. In particular, the present invention pertains to an aircraft cabin having a central aisle and a cross-aisle, and a lavatory that is accessible from the cross-aisle of the aircraft. In the lavatory, the toilet is moved from the typical outboard location to an inboard location where increased head room enables the toilet to be positioned in tight proximity to a back wall of the lavatory directly behind the toilet. This positioning of the toilet increases an open area of floor surface in front of the toilet for wheelchair accessibility. 
     BACKGROUND 
     Commercial aircraft set up for the transportation of passengers typically include rows of seats along the length of the aircraft cabin that are separated by a central aisle and one or more lavatories in the cabin that are accessible from the central aisle. Because the primary purpose of a commercial aircraft is to transport passengers, the aircraft cabin is usually set up to maximize the number of seats in the cabin. As a result, it is challenging to provide adequate lavatory space without reducing seat count. 
     A typical passenger aircraft includes at least one lavatory enclosure that is positioned along the central aisle of the aircraft among the rows of seats. The lavatory enclosure is accessed through a doorway from the central aisle. The width of the lavatory enclosure is typically not much larger than the width of the doorway. The toilet of the lavatory is typically positioned with its back toward an outboard sidewall of the aircraft cabin and its front facing inboard toward the lavatory doorway. Due to the cylindrical configuration of the aircraft body, the sidewall of the aircraft cabin typically curves inwardly or in an inboard direction as it extends upwardly from the floor surface of the aircraft cabin. Because of the curved configuration of the cabin sidewall, the toilet in the lavatory is spaced laterally inwardly or in an inboard direction from the sidewall in order to provide sufficient headroom for a user of the lavatory when standing in front of, or when sitting on the toilet. The need to position the toilet laterally inwardly from the aircraft cabin sidewall to provide adequate head room reduces the area of floor surface between the front of the toilet and the lavatory doorway. This reduced area of floor surface between the toilet and the lavatory doorway makes it difficult for a passenger in a wheelchair to use the lavatory, and in some situations may prevent a passenger in a wheelchair from using the lavatory. 
     SUMMARY 
     The aircraft of the present invention includes a lavatory that overcomes the disadvantages associated with prior art aircraft lavatories discussed above. This is accomplished by reconfiguring the lavatory and repositioning the lavatory toilet in the aircraft cabin away from the outboard sidewall of the aircraft cabin. 
     The lavatory occupies basically the same floor surface area of a typical aircraft lavatory that is accessible through a doorway on the central aisle of the aircraft. The lavatory is positioned adjacent a cross-aisle at the rear of the aircraft cabin at the intersection of the cross-aisle with the central aisle. The lavatory could be positioned in other areas of the aircraft cabin adjacent any cross-aisle. 
     The lavatory includes an inboard back wall this is positioned adjacent the central aisle of the aircraft cabin and is spaced laterally inwardly or inboard from the outboard sidewall of the aircraft cabin. The back wall is substantially flat and extends vertically upwardly from the floor surface to the top of the aircraft cabin, and extends longitudinally through the aircraft cabin between a forward edge and a rearward edge of the back wall. The lavatory also includes a forward sidewall that extends vertically upwardly from the floor surface and laterally through the aircraft cabin between the outboard sidewall of the aircraft cabin and the forward edge of the back wall. The lavatory also includes an aft sidewall positioned at the aft end of the lavatory. The aft sidewall extends vertically upwardly from the floor surface and laterally between the outboard sidewall of the aircraft cabin and the rearward edge of the inboard back wall. The doorway to the lavatory is in the aft sidewall. 
     The toilet of the lavatory is positioned on the floor surface with the back of the toilet adjacent the back wall of a lavatory. The back of the toilet faces toward the back wall and the front of the toilet faces toward the outboard sidewall of the aircraft cabin. Because the back wall is substantially flat as opposed to the vertically curved outboard sidewall of the aircraft cabin, the toilet can be positioned in close proximity to the back wall while still providing adequate head room for a person standing in front of or sitting on the toilet. Additionally, positioning the back of the toilet in tight proximity to the back wall of the lavatory creates an open area of the floor surface in the lavatory between the outboard sidewall of the aircraft cabin and the front of the toilet. The open area of floor surface is dimensioned to accommodate an onboard wheelchair. For example 29 inches by 29 inches. This open area is sufficient to enable an onboard wheelchair that is 13 inches wide and 24 inches deep to be easily rotated in the open area. 
     The doorway through the aft sidewall of the lavatory is accessible from the cross-aisle. The doorway is positioned laterally toward the outboard sidewall of the aircraft cabin and laterally away from the back wall and the toilet of the lavatory. This positions the doorway between the open area of the floor surface dimensioned to accommodate an onboard wheelchair inside the lavatory and the cross-aisle outside of the lavatory. 
     The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features of the aircraft lavatory of the invention are set forth in the following detailed description of the aircraft and in the drawing figures. 
         FIG. 1  is a representation of a portion of a conventional aircraft floor plan at the rear of the aircraft cabin showing the typical locations of lavatories of the aircraft relative to the passenger seating and the galley of the aircraft. 
         FIG. 2  is a representation of the floor plan at the rear of the aircraft of the invention with the lavatory and toilet of the invention. 
         FIG. 3  is a representation of a cross section view of the aircraft cabin and the lavatory and toilet of the invention. 
         FIG. 4  is a representation of an onboard wheelchair in the lavatory of the invention. 
         FIG. 5  is a representation of the open area of floor space in the lavatory of the invention compared to a lavatory of  FIG. 1 . 
     
    
    
     DESCRIPTION 
       FIG. 1  is a representation of the floor plan at the rear of a typical aircraft cabin where lavatories of the aircraft are located. In  FIG. 1  a rearward portion of the aircraft fuselage or body  12  that surrounds the aircraft cabin is shown in cross section. The aircraft cabin has a longitudinal length between a front  14  of the cabin and a rear  16  of the cabin. The cabin also has a lateral width between opposite first  18  and second  22  outboard sidewalls of the aircraft cabin. Due to the cylindrical configuration of the aircraft body, the first  18  and second  22  sidewalls of the cabin curve inwardly or toward the center of the aircraft cabin as they extend vertically upwardly. 
     A plurality of rows of seats  24 ,  26  are arranged on the floor surface  28  of the aircraft cabin. The rows of seats  24 ,  26  are arranged on laterally opposite sides of the cabin and define a central aisle  32 . The central aisle  32  extends longitudinally through the cabin across the floor surface  28  between the front  14  and rear  16  of the cabin and between the rows of seats  24 ,  26 . A galley space or stowage space  34  is provided in the rear of the cabin at the rearward end of the central aisle  32 . 
     A cross-aisle  36  extends laterally across the rear  16  of the cabin in front of the space  34 . The cross-aisle  36  extends between a pair of first  38  and second  42  boarding doors in the respective first  18  and second  22  sidewalls of the aircraft cabin. 
     In the example shown in  FIG. 1 , a traditional aircraft may include three lavatory enclosures  52 ,  54 ,  56 . Each of the enclosures is accessible through a respective door  62 ,  64 ,  66  of the enclosures  52 ,  54 ,  56 . As can be seen in  FIG. 1 , the width dimension of each of the lavatory enclosures  52 ,  54 ,  56  is set in order to maximize the passenger seating in the aircraft cabin. The width of each lavatory enclosure  52 ,  54 ,  56  is not much larger than the width of its respective door  62 ,  64 ,  66 . Each of the lavatory enclosures  52 ,  54 ,  56  contains a respective toilet  68 ,  72 ,  74 . As can be seen in  FIG. 1 , each of the toilets  68 ,  72 ,  74  is spaced laterally inwardly or in an inboard direction from the first  18  and second  22  outboard sidewalls of the aircraft cabin. This is because the first  18  and second  22  sidewalls of the aircraft cabin curve inwardly as the sidewalls extend vertically upwardly from the floor surface  28  of the aircraft cabin. The curved configurations of the sidewalls  18 ,  22  decrease the head room inside the lavatories as the sidewalls are approached from the doorways of the lavatories. 
     In a preferred embodiment, an aircraft is reconfigured such that the lavatory enclosure in a manner that enables the toilet of the lavatory enclosure may be repositioned away from the outboard sidewall of the aircraft cabin and away from the limited head room adjacent the sidewall. 
     As shown in  FIGS. 2 and 3  the lavatory  76  includes a back wall  78  that is positioned adjacent the central aisle  32  and is spaced laterally inwardly or in an inboard direction from the first sidewall  18  of the aircraft cabin. The back wall  78  is substantially flat and extends vertically upwardly from the floor surface  28  to the top of the aircraft cabin. Due to the vertical curvature of the first sidewall  18  of the aircraft cabin, there is significantly more head room adjacent the back wall  78  inside the lavatory  76  than there is adjacent the first sidewall  18 . The back wall  78  also extends longitudinally through the aircraft cabin adjacent the central aisle  32  between a forward edge  82  and a rearward edge  84  of the back wall. The lavatory  76  also includes a substantially flat forward sidewall  86  that extends vertically upwardly from the floor surface  28  to the top of the aircraft cabin. The forward sidewall  86  extends laterally through the aircraft cabin between the first sidewall  18  of the aircraft cabin and the forward edge  82  of the back wall  78 . The lavatory further includes an aft sidewall  88  that extends vertically upwardly from the floor surface  28  to the top of the aircraft cabin. The aft sidewall  88  extends laterally between the rearward edge  84  of the back wall  78  and the first sidewall  18  of the aircraft cabin. A portion of the aft sidewall  92  may curve as it approaches the first cabin sidewall  18  if needed to accommodate a hinge mechanism of the adjacent boarding door  38 . The necessity of this curvature will depend on the location of the lavatory to the boarding door. The doorway  94  to the lavatory  76  is provided through the aft sidewall  88 . The doorway is positioned adjacent to the aft sidewall of the aircraft cabin. A bi-fold door  96  in the doorway  94  is attached to the aft sidewall  88 . The bi-fold door  96  opens into the lavatory  76 . Preferably, the bi-fold construction of the door  96  occupies a minimum amount of space in the lavatory  76  when the door is open. 
     The toilet  102  of the lavatory  76  is positioned on the floor surface  28  inside the lavatory with the back  104  of the toilet adjacent the back wall  78  of the lavatory. With the back  104  of the toilet  102  facing toward the back wall  78 , the front  106  of the toilet faces toward the first sidewall  18  of the aircraft cabin. Because the back wall  78  is substantially flat as opposed to the vertically curved configuration of the first sidewall  18  of the aircraft cabin, the toilet  102  can be positioned in close proximity to the back wall  78  while still providing adequate head room for a person of median height standing in front of or sitting on the toilet  102 . Comparing  FIGS. 1 and 3 , it can be seen that the toilet  102  is positioned significantly closer to the back wall  78  than the toilets  68 ,  72 ,  74  are positioned relative to the first  18  and second  22  sidewalls of the aircraft cabin. Additionally, positioning the back  104  of the toilet  102  in close proximity to the back wall  78  of the lavatory increases the lateral distance or spacing between the front  106  of the toilet  102  and the first sidewall  18  of the aircraft cabin. Increasing the lateral distance of the front  106  of the toilet  102  from the first cabin sidewall  18  creates an open area  108  of the floor surface in the lavatory  76  between the first cabin sidewall  18  and of the front  106  of the toilet. This open area  108  of floor surface, for example 29 inches by 29 inches, is dimensioned to accommodate an onboard wheelchair in the lavatory  76  with the lavatory door  96  closed.  FIG. 4  shows an example of the space occupied by an onboard wheelchair  112  that is 13 inches wide and 24 inches deep in the open area  108  of the floor surface in the lavatory  76 .  FIG. 5  shows the example of the 29 inches by 29 inches open area  114  compared to the floor space of one of the lavatories  52  of  FIG. 1 . 
     As shown in  FIG. 2 , the lavatory door  94  may be positioned laterally toward the first sidewall  18  of the aircraft cabin and laterally away from the back wall  78  and toilet  102  of the lavatory. This positions the doorway  94  between the open area  108  of the floor surface and the cross-aisle  36 . With this positioning of the door  94 , the open area  104  of the floor surface is easily accessible from the cross-aisle  36 . 
     As various modifications could be made in the construction of the invention herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.
An aircraft cabin has a lavatory that is accessible from a cross-aisle of the aircraft and in which the toilet is moved from the typical outboard location to an inboard location where increased head room enables the toilet to be positioned in tight proximity to a back wall of the lavatory directly behind the toilet and thereby increases an open area of floor surface in front of the toilet for wheelchair access to the lavatory.