Patent Publication Number: US-2022212802-A1

Title: Aircraft Lavatory Management System and Method of Assigning a Passenger to a Lavatory within an Aircraft Passenger Cabin

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to, and the benefit of, European Patent Application No. 21150265.3, having DAS code 75D7, filed Jan. 5, 2021 and titled “AIRCRAFT LAVATORY MANAGEMENT SYSTEM AND METHOD OF ASSIGNING A PASSENGER TO A LAVATORY WITHIN AN AIRCRAFT PASSENGER CABIN,” which application is incorporated herein by reference in its entirety for all purposes. 
     FIELD 
     The present invention is in the field of passenger aircraft, in particular in the field of aircraft lavatory management for passenger aircraft. The present invention includes a method of assigning a passenger to a lavatory within an aircraft passenger cabin, an aircraft lavatory management system, which is configured for assigning a passenger to a lavatory within an aircraft passenger cabin, and an aircraft comprising such a lavatory management system. 
     BACKGROUND 
     Passenger aircraft are equipped with a plurality of lavatories for the passengers. Up to now, passengers decide themselves which lavatory they use. This may result in drawbacks such as an inefficient utilization of the lavatories, especially during “rush hours”. With increased utilization of the lavatories, the need for intermediate cleaning/disinfection also rises, which in turn further increases the lavatory bottleneck. This makes it difficult for the aircraft crew to keep the lavatories in a hygienically acceptable condition. Further, long waiting queues in front of the lavatories are unpleasant to the passengers and are counterproductive for ensuring social distancing within an aircraft. 
     It would therefore be beneficial to organize the use of lavatories in an aircraft more efficiently. 
     SUMMARY 
     Exemplary embodiments of the invention include a method of assigning a passenger to a lavatory within an aircraft passenger cabin, wherein the aircraft passenger cabin comprises at least two lavatories, each having a waiting queue, and wherein the aircraft passenger cabin is divided into at least two spatial zones. According to an exemplary embodiment of the invention, the method includes receiving a lavatory assignment request from a passenger. The method further includes determining, based on a seat location of said passenger, a particular spatial zone of the aircraft passenger cabin which includes the seat location of said passenger; and based on the particular spatial zone, adding the passenger to the waiting queue of a particular lavatory, which is associated with the particular spatial zone. The configuration of the at least two spatial zones is variable and it is based on a plurality of zone configuration parameters including a queue length of each of the waiting queues of the at least two lavatories. 
     Exemplary embodiments of the invention further include a lavatory management system for an aircraft passenger cabin comprising at least two lavatories, wherein the lavatory management system includes: a plurality of smart lavatory signs; a plurality of input devices, for example lavatory assignment request buttons, which are configured for allowing passengers to input lavatory assignment requests; and a controller. The controller is configured for receiving lavatory assignment requests from the input devices; adding passengers to the waiting queues of the at least two lavatories employing a method according to an exemplary embodiment of the invention; and providing visual outputs on the plurality of smart lavatory signs, wherein each visual output is indicative of at least a portion of the waiting queue of at least one lavatory. 
     Exemplary embodiments of the invention also include an aircraft comprising a lavatory management system according to an exemplary embodiment of the invention. 
     A method and a lavatory management system according to exemplary embodiments of the invention allow for a more efficient distribution of the lavatory assignment requests across the lavatories, provided within an aircraft passenger cabin. As the lavatory assignment requests are distributed to the different lavatories based on the passengers&#39; respective seating positions within the aircraft, the distances between the passengers and the lavatories, which the passengers are assigned to, may be minimized. 
     Additionally, crossings of the paths of passengers, moving between their seats and the lavatories, may be minimized as well. This may result in an improved social distancing within the aircraft passenger cabin. Further, with the configuration of the at least two spatial zones being variable and being dependent on a plurality of zone configuration parameters, the method and lavatory management system according to exemplary embodiments of the invention may adapt to the varying demand within an aircraft passenger cabin. 
     The method and lavatory management system may dynamically adapt to the current numbers of requests from different parts of the aircraft passenger cabin. A load leveling between the lavatories may be achieved. Above described minimization of passenger path crossings may be achieved in a dynamic manner, without leaving lavatory capacities unused. 
     The assignment of passengers to different lavatories may be restricted to the respective booking classes within the passenger cabin. Load leveling may be performed separately within each of the booking classes. In particular, each booking class that has at least two lavatories may be divided into at least two spatial zones, with the configuration of the at least two spatial zones being variable. More specifically, in such an embodiment, it is possible that passengers from the business class will not be sent to lavatories located within the economy class and vice versa. 
     Alternatively/additionally, passengers from a first booking class may be assigned to lavatories located in a second booking class in case the lavatories in the first booking class have waiting queues that are longer than an overload threshold. In a particular embodiment, passengers from a superior booking class may be assigned to lavatories located in a lower booking class, in order to reduce their waiting times, but passengers from the lower booking class may not be assigned to lavatories located in the superior booking class. In this way, a limited load leveling between booking classes may be achieved, while heavy passenger traffic in the superior booking class may be prevented. 
     In a further embodiment, the lavatory management system may use personal passenger information for adapting the configuration of the at least two spatial zones. The personal passenger information may for example contain the sex or age of the passengers, which are available from the boarding plan of the aircraft. For example, the configuration of the at least two spatial zones may take into account statistical data about the average time of lavatory usage, such as data that women statistically use the lavatories longer than men or data that elderly people statistically use the lavatories longer than younger people. In this way, weighted queue lengths for the at least two lavatories may be determined and may be used for the configuration of the at least two spatial zones. It is also possible that the at least two lavatories are split into two lavatory groups, namely a first lavatory group assigned exclusively to men and a second lavatory group assigned exclusively to women. 
     As stated above, a particular spatial zone is associated with a particular lavatory. In particular, the particular spatial zone may be associated with that lavatory that is closest to the particular spatial zone. 
     Exemplary embodiments of the invention may further allow for reducing the work-load of the cabin crew, maintaining and cleaning the lavatories. Additionally, the formation of passenger crowds in front of the lavatories, which is unfavorable from a hygienic point of view, in particular in pandemic situations, and which is also perceived as annoying by passengers sitting next to the lavatories, may be avoided. 
     According to an embodiment of the invention, the aircraft passenger cabin is divided into said at least two spatial zones by at least one borderline. This at least one borderline is a virtual borderline, i.e. it is not visible to the passengers, and it is used only for the purposes of the lavatory management. The method may include re-configuring at least a subset of the at least two spatial zones by moving at least one borderline based on said plurality of zone configuration parameters. 
     In an embodiment, the at least one borderline includes at least one longitudinal borderline extending along a longitudinal direction of the aircraft, and the step of re-configuring at least a subset of the at least two spatial zones includes moving at least one longitudinal borderline in a transverse direction of the aircraft passenger cabin, in order to adjust the division of the aircraft passenger cabin into multiple spatial zones along the transverse direction. These spatial zones may in particular include a starboard zone and a portside zone. The spatial zones may further include at least one central zone sandwiched between the starboard zone and the portside zone. 
     In an embodiment, the at least one borderline includes at least one transverse borderline extending in a transverse direction of the aircraft passenger cabin, in particularly orthogonally to the longitudinal direction of the aircraft, and the step of re-configuring at least a subset of the at least two spatial zones includes moving at least one transverse borderline in a longitudinal direction of the aircraft passenger cabin, in order to adjust the division of the aircraft passenger cabin into multiple spatial zones along the longitudinal direction. These zones may in particular include a front zone and a rear zone. The zones may further include at least one middle zone sandwiched between the front zone and the rear zone. 
     The implementation of such virtual borderlines has been found as allowing a very efficient adjustable/variable division of the aircraft passenger cabin into multiple spatial zones. 
     The movement of the borderlines may include reducing the number of spatial zones by moving at least two adjacent borderlines to the same position. Reducing the number of spatial zones may be beneficial for enhancing the efficiency of the method, for example in situations in which at least one of the lavatories is not available due to maintenance or malfunction. 
     In an embodiment, the method includes providing a visual indication of the particular lavatory, whose waiting queue the passenger has been added to. This may in particular include a visual indication at the passenger space close to or at the passenger&#39;s seat and/or at a lavatory sign, which is provided next to the respective lavatory. 
     In case the visual indication is provided at the passenger space, the visual indication may in particular include information indicating the lavatory, whose waiting queue the passenger has been added to, in order to allow the passenger to identify the lavatory which he/she has been assigned to. 
     In case the visual indication is provided at a lavatory, the visual indication will include information identifying the passenger, for example a passenger ID/boarding number or the number of the passenger&#39;s seat. 
     According to an embodiment, the method includes re-configuring the at least two spatial zones in accordance with a predetermined re-configuration schedule. The method may in particular include re-configuring the at least two spatial zones in periodic intervals, and/or after the receipt of each lavatory assignment request. Re-configuring the at least two spatial zones in accordance with a predetermined re-configuration schedule results in regularly adjusting the distribution of the lavatory assignment requests according to the current load distribution. In this way, a very efficient distribution scheme of the lavatory assignment requests over the at least two waiting queues may be regularly established. 
     According to an embodiment, the plurality of zone configuration parameters further include at least one of: an “in service”/“out of service” indication for each of the at least two lavatories; for each of the at least two lavatories, a total number of passengers, who have used the respective lavatory since its last maintenance and/or cleaning; and scheduled service times for each of the at least two lavatories. 
     According to an embodiment, the plurality of smart lavatory signs, the plurality of input devices, and the controller are configured for communicating with each other by a wired or by a wireless data transmission. The wireless data transmission in particular may include WLAN, Bluetooth®, or optical, such as infrared, data transmission. 
     Smart lavatory signs, input devices and a controller, which are configured for communicating by wireless data transmission, may be added to an aircraft passenger cabin without the need for modifying the existing wiring within said aircraft passenger cabin. In consequence, the installation of a lavatory management system according to an exemplary embodiment of the invention may be carried out in a minimally invasive manner. Retrofitting existing aircraft with lavatory management systems according to exemplary embodiments of the invention may be achieved in a comparably easy manner. 
     In an embodiment, at least one of the smart lavatory signs and/or of the input devices may be configured as a relay, i.e. at least one of the smart lavatory signs and/or of the input devices may be configured for receiving information from at least one other smart lavatory sign and/or input device and for forwarding the received information to another smart lavatory sign or input device. This may allow transmitting information between the smart lavatory signs and/or the input devices over large distances, using short wires and/or an energy-efficient short-range wireless data transmission. 
     In an embodiment, the smart lavatory signs are provided at the passenger seats, in particular at armrests of the passenger seats or in passenger service units located above the passenger seats. Alternatively or additionally, smart lavatory signs may be provided at the lavatories and/or at the ceiling of the aircraft passenger cabin. 
     In an embodiment, the controller is integrated into one of the plurality of smart lavatory signs or into one of the plurality of input devices. A master-slave-configuration may be established, in which the lavatory sign or the input device comprising the controller acts as the “master”, controlling the operation of the other smart lavatory signs and input devices (“slaves”). 
     In an embodiment, a respective controller is integrated into at least two of the plurality of smart lavatory signs or the plurality of input devices, in order to provide an additional second controller as a backup, which is activated in case the first controller should fail. 
     In an embodiment, the lavatory management system is additionally configured for at least one of the following, in particular for any subset of the following:
         issuing a service request to the aircraft crew, for example in case one of the lavatories needs to be maintained and/or cleaned;   deactivating at least one of the lavatories and closing/shutting down the waiting queue of said lavatory, for example in case the lavatory is defect or needs to be maintained and/or cleaned; deactivating at least one of the lavatories may include locking the door of said lavatory in order to prevent unauthorized access to the lavatory;   unlocking and activating at least one of the lavatories and re-opening the waiting queue of said lavatory, for example after the lavatory has been repaired, maintained and/or cleaned;   activating and/or deactivating ventilation of at least one of the lavatories, in particular depending on it most recent use;   activating a disinfection process of at least one of the lavatories, in particular depending on its most recent use;   controlling visual status indicators, indicating the status of at least one of the lavatories, wherein the status may in particular include “free”, “occupied”, “out of order”, or “blocked for maintenance”.       

     Such a lavatory management system may allow for a very efficient use of the lavatories provided within an aircraft passenger cabin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, exemplary embodiments of the invention are described with respect to the accompanying drawings, wherein: 
         FIG. 1  depicts a schematic cross-sectional view of an aircraft passenger cabin, which is divided in a first configuration comprising four spatial zones. 
         FIG. 2  depicts a schematic cross-sectional view of the aircraft passenger cabin of  FIG. 1 , divided in a second configuration comprising four spatial zones. 
         FIG. 3  depicts a schematic cross-sectional view of the aircraft passenger cabin of  FIG. 1 , divided in a configuration comprising two spatial zones. 
         FIG. 4  shows a schematic view of a smart lavatory sign, as may be employed in a lavatory management system according to an exemplary embodiment of the invention. 
         FIG. 5  depicts a schematic view of an overhead passenger service unit comprising input devices, as may be employed in a lavatory management system according to an exemplary embodiment of the invention. 
         FIG. 6  depicts a schematic view of an armrest passenger service unit comprising an input device, as may be employed in a lavatory management system according to an exemplary embodiment of the invention. 
         FIG. 7  depicts a schematic view of a lavatory management system according to an exemplary embodiment of the invention. 
         FIGS. 1 to 3  depict three schematic cross-sectional views of a passenger cabin  2  of an aircraft  1 , also referred to as aircraft passenger cabin  2  herein. 
     
    
    
     DETAILED DESCRIPTION 
     The aircraft passenger cabin  2  is equipped with a plurality of passenger seats  4 . The passenger seats  4  are arranged next to each other forming a plurality of passenger seat rows. Each passenger seat row comprises two groups of passenger seats  4 , respectively including three passenger seats  4 . The two groups of passenger seats  4  are separated from each other by an aisle  14  extending along a longitudinal axis A of the aircraft  1 . 
     The aircraft passenger cabin  2  is further equipped with four lavatories  6   a - 6   d . In the exemplary configuration depicted in  FIGS. 1 to 3 , lavatories  6   a - 6   d  are provided at four locations within the aircraft passenger cabin  2 . A first lavatory  6   a  is located at the front portside end of the aircraft passenger cabin  2 , a second lavatory  6   b  is located at the front starboard end of the aircraft passenger cabin  2 , a third lavatory  6   c  is located at the rear portside end of the aircraft passenger cabin  2 , and a fourth lavatory  6   d  is located at the rear starboard end of the aircraft passenger cabin  2 . 
     According to an exemplary embodiment of the invention, the aircraft passenger cabin  2  is divided into a plurality of spatial zones  8   a - 8   d . In the exemplary configurations depicted in  FIGS. 1 and 2 , the aircraft passenger cabin  2  is divided into four spatial zones  8   a - 8   d  by a longitudinal borderline  10  extending along a longitudinal axis A of the aircraft  1 , and by a transverse borderline  12 , which extends perpendicularly to the longitudinal borderline  10  and the longitudinal axis A of the aircraft  1 . 
     The borderlines  10 ,  12  are “virtual” borderlines, i.e. the borderlines  10 ,  12  are not visible to the passengers  5  and they are used only for the purposes of lavatory management, as it is described in the following. 
     In the embodiment depicted in  FIG. 1 , the longitudinal borderline  10  extends along the aisle  14  through the longitudinal axis A of the aircraft  1  separating the aircraft passenger cabin  2  into a starboard portion  8   b ,  8   d  and a portside portion  8   a ,  8   c , respectively comprising basically the same number of passenger seats  4 . Similarly, the transverse borderline  12  is arranged at a basically central position along the longitudinal extension of the aircraft passenger cabin  2 , so that the transverse borderline  12  separates the aircraft passenger cabin  2  into a front portion  8   a ,  8   b  and a rear portion  8   c ,  8   d , respectively comprising basically the same number of passenger seats  4 . 
     As a result, the four spatial zones  8   a - 8   d  comprise basically the same number of passenger seats  4 . 
     Each spatial zone  8   a - 8   d  is associated with one of the lavatories  6   a - 6   d.    
     In particular, each spatial zone  8   a - 8   d  is associated with the lavatories  6   a - 6   d  located within the respective spatial zone  8   a - 8   d . In other words, the first spatial zone  8   a  is associated with the first lavatory  6   a , the second spatial zone  8   b  is associated with the second lavatory  6   b , the third spatial zone  8   c  is associated with the third lavatory  6   c , and the fourth spatial zone  8   d  is associated with the second lavatory  6   d.    
     The aircraft passenger cabin  2  is equipped with a lavatory management system (LMS)  50  (cf.  FIG. 7 ), which is configured for managing lavatory assignment requests  48 , issued by passengers  5  within the aircraft passenger cabin  2 . 
     The LMS  50  comprises four waiting queues  60   a - 60   d  (cf.  FIG. 7 ), each waiting queue  60   a - 60   d  being associated with one of the lavatories  6   a - 6   d , respectively. 
     When a passenger  5  desires to use a lavatory, the passenger  5  issues a lavatory assignment request  48  via an input device  30   a - 30   c  (see  FIGS. 5 to 7 ), for example by pressing lavatory assignment request button  30   a - 30   c . Each passenger  5  is provided with his personal input device, which is located at his passenger seat  4 . Exemplary embodiments of input devices/lavatory assignment request buttons  30   a - 30   c  are depicted in  FIGS. 5 and 6 , which will be discussed further below. 
     Every lavatory assignment request  48 , issued by a passenger  5 , is received by the LMS  50 , and the LMS  50  determines the location of the seat  4  of the passenger  5  issuing the request. 
     Based on the seat location of the passenger  5  issuing the request, the LMS  50  determines the spatial zone  8   a - 8   d  of the aircraft passenger cabin  2 , in which the seat  4  of the passenger  5  issuing the request is located. The passenger&#39;s lavatory assignment request  48  is then added to the waiting queue  60   a - 60   d  of the lavatory  6   a - 6   d  which is associated with the determined spatial zone  8   a - 8   d.    
     Referring in particular to the exemplary configurations depicted in  FIG. 1 , the passenger&#39;s request will be added to the waiting queue  60   a - 60   d  of the first lavatory  6   a , if the passenger&#39;s seat  4  is located in the first spatial zone  8   a ; the passenger&#39;s request will be added to the waiting queue  60   a - 60   d  of the second lavatory  6   b , if the passenger&#39;s seat  4  is located in the second spatial zone  8   b ; the passenger&#39;s request will be added to the waiting queue  60   a - 60   d  of the third lavatory  6   c , if the passenger&#39;s seat  4  is located in the second third zone  8   c ; and the passenger&#39;s request will be added to the waiting queue  60   a - 60   d  of the fourth lavatory  6   d , if the passenger&#39;s seat  4  is located in the fourth spatial zone  8   d.    
     A soon as a lavatory assignment request  48  has been received, a confirmation signal, indicating that the passenger request has been received by the LMS  50 , may be issued. The confirmation signal may include at least one of a visual signal, an acoustic signal and a tactile signal. 
     For example, the passenger request button  30   a - 30   c , which is used for issuing the lavatory assignment request  48 , may light up and/or vibrate, in order to confirm the request. Alternatively or additionally, the confirmation signal may be output via at least one of a plurality of smart lavatory signs  16   a - 16   d , provided within the aircraft passenger cabin  2 . A smart lavatory sign  16   a - 16   d  allows for dynamically changing the information which is given by the smart lavatory sign  16   a - 16   d  to the passengers  5 . 
     In addition to providing a confirmation signal, the smart lavatory sign  16   a - 16   d  may indicate the waiting queue  60   a - 60   d  and/or the lavatory  6   a - 6   d  to which the passenger&#39;s lavatory assignment request  48  has been added, and the position of the passenger&#39;s request within said waiting queue  60   a - 60   d.    
     The waiting queues  60   a - 60   d  of the lavatories  6   a - 6   d  may be processed following the first-in-first-out (FIFO) principle. I.e. as soon as a lavatory  6   a - 6   d  is reported as being available, the passenger  5 , which issued the first lavatory assignment request  48  within the waiting queue  60   a - 60   d , associated with said lavatory  6   a - 6   d , is assigned to said lavatory  6   a - 6   a . The passenger  5  is then invited to the assigned lavatory  6   a - 6   d  by a visual output, which is output on at least one smart lavatory sign  16   a - 16   d . The visual output indicates the passenger  5 , in particular the boarding number or the seat  4  of the passenger  5 , and the lavatory  6   a - 6   d , the passenger  5  is assigned to. 
     In an optional embodiment, the average waiting times of passengers sitting in a more expensive class, such as the first class or a business class, may be reduced by prioritizing the lavatory assignment requests  48  of those passenger  5  over the lavatory assignment requests  48  of passengers  5  sitting in a less expensive class, such as an economy class. 
     Smart lavatory signs  16   a - 16   d  may be provided at the lavatories  6   a - 6   d , at the passenger seats  4 , and/or at other positions within the aircraft passenger cabin  2 , which are well visible to the passengers  5 . Entertainment displays (not shown) located at the passenger seats  4  may be employed as smart lavatory signs  16   a - 16   d  as well. 
     A smart lavatory sign  16   a - 16   d  may in particular be provided next to each passenger request buttons  30   a - 30   c , in order to show the assignments of the requests, input via the respective passenger request button  30   a - 30   c.    
     The configuration of the aircraft passenger cabin  2 , depicted in  FIGS. 1 to 3 , is only exemplary. The skilled person understands that other configurations of the aircraft passenger cabin  2  are possible as well. Such configurations in particular may include configurations comprising more or less rows of passenger seats  4 , configurations, in which more or less than six passenger seats  4  are arranged in each row, and the passenger seats  4  in each row may be separated by more than one aisle  14 . Further, the aircraft passenger cabin  2  may be equipped with more or less than four lavatories  6   a - 6   d  and smart lavatory signs  16   a - 16   d , and the lavatories  6   a - 6   d  and the smart lavatory signs  16   a - 16   d  may be located at other positions than the positions depicted in  FIGS. 1 to 3 . 
     The configuration of the spatial zones  8   a - 8   d , depicted in  FIG. 1 , minimizes the distances between each passenger  5  and the lavatory  6   a - 6   a  the passenger  5  is assigned to. I.e. in the configuration depicted in  FIG. 1 , each passenger  5  is added to the waiting queue  60   a - 60   d  of the lavatory  6   a - 6   d , which is closest to his/her seat  4 . 
     This simple assignment scheme however, may not always result in the most efficient assignment of the lavatory assignment requests  48 . For example, at a given point in time, the first and second lavatories  6   a ,  6   b , located in the front portion  8   a ,  8   b  of the aircraft passenger cabin  2 , may be used more heavily than the third and fourth lavatories  6   c ,  6   d , located in the rear portion  8   c ,  8   d  of the aircraft passenger cabin  2 . 
     In such a situation, although the seat  4  of a passenger  5 , issuing a lavatory assignment request  48 , may be located closer to one of the lavatories  6   a ,  6   b  located in the front portion of the aircraft passenger cabin  2 , it may be more efficient to assign said passenger request to one of the lavatories  6   c ,  6   d  located in the rear portion of the aircraft passenger cabin  2 , in order to reduce the passenger&#39;s waiting time. 
     Thus, according to exemplary embodiments of the invention, the configuration of the spatial zones  8   a - 8   d  is not static, but variable. In other word, a LMS  50  according to an exemplary embodiment of the invention dynamically adjusts the configuration of the spatial zones  8   a - 8   d , based on predefined zone configuration parameters. The predefined zone configuration parameters in particular may include the lengths of the waiting queues  60   a - 60   d  of the lavatories  6   a - 6   d.    
       FIG. 2  illustrates an example, in which the first and second lavatories  6   a ,  6   b , located in the front portion  8   a ,  8   b  of the aircraft passenger cabin  2 , have been—according to the configuration of the spatial zones of  FIG. 1 —requested more frequently than the third and fourth lavatories  6   c ,  6   d , located in the rear portion  8   c ,  8   d  of the aircraft passenger cabin  2 . 
     In consequence, the virtual transverse borderline  12 , which extends perpendicularly to the longitudinal direction of the aircraft passenger cabin  2 , and which divides the aircraft passenger cabin  2  into front spatial zones  8   a ,  8   b  and rear spatial zones  8   c ,  8   d , is moved towards the front end of the aircraft passenger cabin  2 . As a result, the rear spatial zones  8   c ,  8   d  comprise more passenger seats  4  than the front spatial zones  8   a ,  8   b.    
     In consequence, lavatory assignment requests  48  from passengers, sitting in zones  81 ,  82  in a middle portion of the aircraft passenger cabin  2 , who would have been assigned to the first or second lavatories  6   a ,  6   b  in the configuration depicted in  FIG. 1 , will now be assigned to the third or fourth lavatories  6   c ,  6   d , in order to balance the load of the lavatories  6   a - 6   d  and to minimize the average waiting times of the passengers  5 . 
     Although not explicitly shown in the figures, the skilled person understands that the position of the virtual longitudinal borderline  10  may be adjusted similarly in addition or alternatively to the described adjustment of the virtual transverse borderline  12  in case of an unbalanced usage of the lavatories located on the portside and on the starboard side of the aircraft passenger cabin  2 . 
     The configuration of the spatial zones  8   a - 8   d  may be re-configured in accordance with a predetermined re-configuration schedule, for example in periodic intervals, and/or after a predefined number lavatory assignment requests  48  have been received. 
     The LMS  50  may also monitor the waiting times of the passengers  5  and re-configure the configuration of the spatial zones  8   a - 8   d  if an imbalance between the waiting times of the individual lavatories  6   a - 6   d  is detected. 
     An LMS  50  according to an exemplary embodiment of the invention may further be configured for handling situations in which at least one of the lavatories  6   a - 6   d  is not available, e.g. due to a technical defect or due to maintenance and/or cleaning. 
     An example of such a situation is depicted in  FIG. 3 . In said example, the third and fourth lavatories  6   c ,  6   d  located at the rear end of the aircraft passenger cabin  2  are not available. Therefore, the virtual transverse borderline  12  is moved to the very rear end of the aircraft passenger cabin  2 . In consequence, the number of spatial zones  8   a - 8   d  into which the aircraft passenger cabin  2  is divided, is reduced from four (in  FIGS. 1 and 2 ) to two (in  FIG. 3 ), and all lavatory assignment requests  48  are assigned to the first and second lavatories  6   a ,  6   b , located in the front portion  8   a ,  8   b  of the aircraft passenger cabin  2 . 
     This prevents passengers  5  from approaching the lavatories  6   c ,  6   d  located at the rear end of the aircraft passenger cabin  2 , only to learn that these lavatories  6   c ,  6   d  are not available for use. 
     Similarly, the configuration of the spatial zones  8   a - 8   d  may be adjusted appropriately in case the first and second lavatories  6   a ,  6   b , located at the front end of the aircraft passenger cabin  2 , are not available or lavatories located on one lateral side of the aircraft passenger cabin  2  are not available or a single lavatory is not available. 
       FIG. 4  shows a schematic view of a smart lavatory sign  16 , as may be employed in a lavatory management system according to an exemplary embodiment of the invention. 
     The smart lavatory sign  16  comprises a display  18 , e.g. an LED display or an LCD display  18 , which is divided into at least four portions  20   a - 20   d . Alternatively the smart lavatory sign  16  may comprise a plurality of separate displays  20   a - 20   d.    
     In the first portion  20   a  of the display  18 , the seat  4 , which is identified by its row (“25”) and column (“A”), of the passenger that is currently being invited into a lavatory is indicated. The color of the information, shown in the first portion  20   a , may change, e.g. between red and green or any other colors, and/or the information may flash depending on whether the passenger  5  has already entered the lavatory  6   a - 6   d  or not. 
     Optionally, the first portion  20   a  of the display  18  may additionally indicate the particular lavatory the passenger  5  is assigned to (“L1”), in particular in configurations in which the smart lavatory sign  16  is not located next to the respective lavatory  6   a - 6   d.    
     As long as the passenger  5  has not entered the lavatory  6   a - 6   d  he is assigned to, a countdown  17  may be displayed in the first portion  20   a  indicating how long the respective lavatory  6   a - 6   d  will be reserved for the respective passenger  5 . If the countdown  17  runs down, before the assigned passenger  5 , has entered the lavatory  6   a - 6   d , the lavatory  6   a - 6   d  will be assigned to the next passenger  5  in the waiting queue  60   a - 60   d . The first portion  20   a  of the displays  18  may flash during the last seconds of the countdown  17 . 
     The seats of the passengers, who are next in the waiting queue  60   a - 60   d  of the respective lavatory  6   a - 6   d , are displayed in the second to fourth portions  20   b - 20   d  of the display  18 . This allows the passengers  5  to estimate their respective waiting times and to prepare for timely approaching and entering the lavatory  6   a - 6   d  they are assigned to. 
     The smart lavatory sign  16  may further comprise a visual status indicator  19 , which is configured for indicating the status of the respective lavatory  6   a - 6   d . The status of the lavatory  6   a - 6   d , which for example may include “free”, “occupied”, “out of order”, “blocked for maintenance”, may be indicated by different colors, graphical signs, or texts. 
       FIG. 5  depicts a schematic view of an overhead passenger service unit (PSU)  22 , which is arranged above the passengers of a single passenger row, as it is seen from the side of a passenger  5  sitting on a passenger seat  4  below the overhead passenger service unit  22 . 
     On the side, which is shown to the left in  FIG. 5 , the overhead passenger service unit  22  comprises a row of three adjustable reading lights  26   a - 26   c , which are arranged next to each other. 
     Six electrical switches  27   a - 27   c ,  28   a - 28   c  are provided to the right side of the reading lights  26   a - 26   c , a pair of two switches  27   a - 27   c ,  28   a - 28   c  next to each of the reading lights  26   a - 26   c  respectively. One of the switches  27   a - 27   c  of each pair is configured for switching the adjacent reading light  26   a - 26   c , and the second switch  28   a - 28   c  of each pair is configured as for triggering a signal for calling cabin service personnel. 
     A row of three adjacent gaspers  29   a - 29   c  arranged in the lateral direction is provided next to the switches  27   a - 27   c ,  28   a - 28   c.    
     Next to the gaspers  29   a - 29   c , there are three input devices/lavatory assignment request buttons  30   a - 30   c , which allow passengers  5  to input lavatory assignment requests  48  by pressing the respective lavatory assignment request button  30   a - 30   c . One of the assignment request buttons  30   a - 30   c  is assigned to each seat  4 , respectively. 
     The lavatory assignment request buttons  30   a - 30   c  may be configured for providing a feedback that a respective lavatory assignment request  48  has been received, for example by lighting up, changing their color and/or providing a tactile feedback, such as vibration. 
     Next to the lavatory assignment request buttons  30   a - 30   c  is a removable cover  40 , which covers a cavity housing at least three oxygen masks (not shown). In the event of pressure loss within the cabin, the removable cover  40  will open, the oxygen masks will drop out of the cavity and each of the passengers  5 , sitting below the overhead passenger service unit  22 , may grasp one of the oxygen masks. The oxygen masks will be supplied with oxygen allowing the passengers  5  to continue to breathe normally. 
     On the side opposite to the gaspers  29   a - 29   c , a grid  42  is formed within overhead passenger service unit  22 . A loudspeaker (not shown), which may be used for delivering acoustic announcements to the passengers  5 , is arranged behind said grid  42 . 
     Next to the grid  42 , there is a display panel  44 , which may be configured for selectively showing a plurality of visual signs (not shown), such as “non-smoking” or “fasten your seat belt”. The display panel  44  may be illuminated from behind, in order to deliver visual information to the passengers  5  sitting below the overhead passenger service unit  22 . 
     The display panel  44  may also be configured as a smart lavatory sign  16  for providing information from the LMS  50  to the passengers  5 . This information may include an acknowledgment that a lavatory assignment request  48  has been received, an indication of the lavatory  6   a - 6   d , the passenger  5  is assigned to, and the position of the passenger&#39;s lavatory assignment request  48  within the respective waiting queue  60   a - 60   d.    
     An alternative embodiment of a passenger service unit  22 , which in particular may be arranged in an armrest of a passenger seat  4 , is depicted in  FIG. 6 . 
     In the configuration depicted in  FIG. 6 , an individual passenger service unit  22  is assigned to each passenger seat  4 , and the passenger service unit  22  comprises a plurality of control buttons  32  for controlling an aircraft entertainment system. 
     The selection and the arrangements of the individual components and switches/buttons of the passenger service unit  22 , depicted in  FIGS. 5 and 6 , are only exemplary. The components and switches/buttons of the passenger service units  22  may be arranged differently, depending on the actual needs. 
       FIG. 7  depicts a schematic view of a LMS  50  according to an exemplary embodiment of the invention as a block diagram. 
     The LMS  50  comprises a plurality of smart lavatory signs  16   a - 16   d , which may be arranged next to the lavatories  6   a - 6   d , in the passenger service units  22  or at other suitable positions within aircraft passenger cabin  2 . 
     The LMS  50  further comprises a plurality of lavatory assignment request buttons  30   a - 30   c , allowing passengers to input lavatory assignment requests  48 . 
     The smart lavatory signs  16   a - 16   d  and the input devices  30   a - 30   c  communicate with each other via a communication network  52 . 
     The communication network  52  may be a wired network  52  or a wireless network  52  or a combination thereof. The smart lavatory signs  16   a - 16   d  and the input devices  30   a - 30   c  may in particular be configured for communicating with each other using WLAN and/or Bluetooth® technology. The smart lavatory signs  16   a - 16   d  and the input devices  30   a - 30   c  may also be configured for communicating via optical data transmission, in particular employing infrared light. 
     An LMS  50 , which is configured for communicating via a wireless communication network  52 , may be added to an aircraft passenger cabin  2  without the need for modifying the existing wiring within said aircraft passenger cabin  2 . 
     In such a communication network  52 , at least one of the smart lavatory signs  16   a - 16   d  and/or the input devices  30   a - 30   c  may be configured as a relay, i.e. at least one of the smart lavatory signs  16   a - 16   d  and/or input devices  30   a - 30   c  may be configured for receiving information from at least one other smart lavatory sign  16   a - 16   d  and/or input devices  30   a - 30   c  and for forwarding the received information to another smart lavatory sign  16   a - 16   d  or input device  30   a - 30   c . Such a configuration may allow for transmitting information between the smart lavatory signs  16   a - 16   d  and/or input devices  30   a - 30   c  over large distances using short wires and/or an energy-efficient short-range wireless data transmission. It is further possible that a majority or all of the smart lavatory signs and the input devices are configured as relays. 
     In the exemplary embodiment depicted in  FIG. 7 , the LMS  50  is implemented in a master-slave-configuration. I.e. one of the smart lavatory signs  16   a - 16   d , in the embodiment depicted in  FIG. 7  the first smart lavatory sign  16   a , is implemented as a “master” comprising a controller  54 , which is configured for providing the central functionalities of the LMS  50 . The controller  54  receives the lavatory assignment requests  48  from lavatory assignment request buttons  30   a - 30   c  and assigns the lavatory assignment requests  48  to the waiting queues  60   a - 60   d  of the different lavatories  6   a - 6   d , as it has been described with respect  FIGS. 1 to 3 . The controller  54  also re-configures the spatial zones  8   a - 8   d  of the aircraft passenger cabin  2 , if necessary, as it has been described before. 
     The waiting queues  60   a - 60   d  of the different lavatories  6   a - 6   d  may be managed centrally by the controller  54 . In an alternative configuration, the individual smart lavatory signs  16   b - 16   d  maybe configured for managing their respective waiting queues  60   a - 60   d  autonomously. In the latter configuration, the smart lavatory signs  16   a - 16   d  are configured for supplying a signal indicating the current length of their respective waiting queues  60   a - 60   d  to the controller  54 , in order to allow the controller  54  to re-configure the spatial zones  8   a - 8   d  of the aircraft passenger cabin  2  in case of an unbalanced distribution of the lavatory assignment requests  48 . 
     At least one further smart lavatory sign  16   b - 16   d  may be additionally provided with controller functionalities for providing a backup controller  56 , which may replace the controller  54  in case of a malfunction. 
     In another embodiment, the at least one controller  54 ,  56  is provided separately from the smart lavatory signs  16   b - 16   d.    
     The LMS  50  may be connected with an aircraft system/aircraft passenger cabin management system  58 , in order to allow for adjusting the operating of the LMS  50  based on information received from the aircraft system/aircraft passenger cabin management system  58 . This may include, for example, blocking access to the lavatories  6   a - 6   d  during take-off and landing of the aircraft  1  and/or during unsafe flight conditions, such as heavy turbulences. 
     Optional functionalities of the LMS  50  may further include at least one of the following, in particular any subset of the following: deactivating at least one of the lavatories  6   a - 6   d  and issuing a service request to the aircraft crew in case a malfunction of a lavatory  6   a - 6   d  has been detected; locking the deactivated lavatory  6   a - 6   d  in order to prevent unauthorized access to the lavatory  6   a - 6   d ; re-activating and unlocking the at least one lavatory  6   a - 6   d  after the problem has been fixed; selectively activating and/or deactivating ventilation of at least one of the lavatories  6   a - 6   d , in particular based on its use; activating a disinfection process of at least one of the lavatories  6   a - 6   d , in particular based on its use, for example after the lavatory  6   a - 6   d  has been used by a predefined number of passengers  5 . 
     While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adopt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention include all embodiments falling within the scope of the following claims.