1.  Field of the Invention
The field of the invention is that of the flow of aircraft traffic over the airport areas before they takeoff or after they have landed and of the electronic and data processing means allowing the route to be followed over these areas to be indicated to the crews. 
2.  Description of the Prior Art
Conventionally, during taxiing phases over an airport area, the pilots receive taxiing instructions from the air traffic control or ATC.  FIG.  1 shows a partial plan view of an airport area Z. In this area, the aircraft A situated on the taxiway B must get to the takeoff runway “27L” appearing in black in FIG.  1.  The pilot will receive a taxiing instruction indicating to him for example to go via the taxiways “BD20” and “Y11”.  An ATC instruction authorizing the taxiing is also called taxiing clearance.  These instructions give pilots the authorization to taxi up to a certain point without fear of any conflict with another aircraft or another vehicle.  The ATC communicates this information by voice and the pilots remember it and may write it down on paper or in a text input area, such as a “scratchpad”, of an electronic control unit.  This unit can be an MCDU, acronym for “Multi Control Display Unit”.  The pilots then use paper maps to locate themselves within the airport area and follow the route indicated. 
Currently, some onboard systems can calculate the route to be followed based on these instructions and display this route on electronic airport maps in order to simplify the navigation task of the pilots.  The system must therefore recognize the clearances perfectly in order to be able to process them and display them. 
Several solutions are possible for inputting the clearances.  Indeed, the clearance can be entered into the system:                Either automatically, by receiving the information needed for the display of the clearance via a digital link or by voice recognition;        Or through manual intervention by the pilot.  In the latter case, he inputs the ATC instruction as a text which is then interpreted by the system and then displayed on the map.  The input operation can be carried out on a touch screen and read by a writing recognition system or more simply, the input can be done on an alphanumeric keyboard.         
In the case of a manual intervention by the pilot, inputting on an alphanumeric keyboard offers the advantage of being able to use editing means such as the MCDU units already present on many aircraft. 
In general, the taxiing instructions indicate the destination which, by way of example, might be “holding position”, “stand”, “runway” then the route to be followed composed of names of taxiways.  Thus, an instruction generally takes the following form:
TAXI TO [Halt Position] VIA [Specific Route to be Followed]
In order to input an instruction without ambiguities, this instruction must be input by introducing a separator between each airport element so as to allow the system to easily find it and without errors in a database.  For example, the instruction ATC: “TAXI TO stand E10 VIA taxiways T40, T41 and M2” corresponds to the pilot inputting the following: “E10-T40-T41-M2”.  However, the addition of a separator between each element adds a workload for the pilot who runs the risk of not having the time to input the complete instruction dictated to him by the ATC.