1. Field of the Invention
This invention concerns a device for assistance with interception by an aircraft for a flight path segment located in a horizontal plane, and a system for assistance with the interception and follow-up of such a segment.
2. Description of Related Art
In general, when an aircraft pilot, for instance flying a helicopter, wishes to intercept a flight path in the horizontal plane, he has to perform the following operations:                identify the flight path part (segment) to be reached, and take a heading for its interception allowing for the effect of wind, if known;        anticipate the turning of the aircraft to join the flight path without overshoot, depending on the speed of the aircraft and the angle of interception; and        ensure that the interception flight path is reliable with respect to ground and any nearby obstacles.        
The precision required to follow an intercepted flight path, including a multitude of segments, varies along said flight path. Accordingly, the flight path monitoring accuracy is far greater during final approach than during cruise flight phases.
It is known that the pilot in the approach phase in a horizontal plane uses ILS (Indicator Landing System) type information, displayed by dedicated symbology of varying sensitivity, which is constantly increasing as the aircraft approaches the touchdown point. Conversely, during the cruise phase, in order to provide sufficient accuracy, a flight path segment monitoring procedure in the horizontal plane requires the pilot to select the most appropriate scale at a given moment, so as to comply with the required precision and/or use flight path deviation digital information combined with another dedicated symbology, for instance an HIS (Horizontal Situation Indicator).
Accordingly, the pilot following the current flight phase must make various selections and gather appropriate flight path deviation information to follow at various positions of the display screen (and even on two different screen pages), which information is generally presented using different formalisms.
Furthermore, during the periods of intense workload encountered by the pilot, omitting to modify a scale can have damaging consequences. Indeed, the pilot may believe erroneously that the aircraft is properly aligned on the flight path to follow whereas, in reality, the selected scale is too large.
Finally, in order to accomplish with satisfactory accuracy, the complete procedure demands a great deal of know-how and also intense attention and activity (high workload) throughout the interception and follow-up duration. Note that organization and dosing difficulties are essentially due to the fact that the customary instruments and/or symbologies used are not organized to present an obvious synthesis of the effective situation.
This invention concerns a device assisting with interception by an aircraft of a flight path segment located in a horizontal plane designed to remedy these drawbacks.
Indeed, according to the invention, said device assisting with interception by an aircraft of a flight path segment located in a horizontal plane, said device being brought abroad the aircraft and including:                initial resources for determining the values of the aircraft parameters; and        initial display resources to present on at least one display screen:                    at least said flight path segment in the horizontal plane to be intercepted; and            an initial symbol illustrating the position of the aircraft in the horizontal plane with respect to said flight path,is outstanding in that the initial resources determine at least one ground speed vector representative of the speed of the aircraft with respect to the ground and in that said initial display resources are liable to present, in addition, on said display screen:                        a first means of indicating the ground speed corresponding to a first rectilinear section in said horizontal plane connected to said symbol whose angular orientation corresponds to the direction of said ground speed vector and whose length:                    is proportional to the ground speed vector module when said ground speed is greater than a predetermined value; and            is fixed and proportional to the module of said predetermined value when said ground speed is less than or equal to this predetermined value;                        a second means of interception approach indication, corresponding to a second rectilinear in said horizontal plane, in the direction of said flight path segment to be intercepted and whose length adjusts automatically so that said second rectilinear section extends at one of its ends, said first rectilinear section and at the other of its ends, a third means of indication; and        said third means of interception turn indication, corresponding to a curve portion including at least one circle arc in said horizontal plane, one end of said curve portion extending at a tangent into second rectilinear section and, at the other end, connected at a tangent to said flight path to be intercepted.        
All this graphic information forms the flight path interception path which ends, if there is no flight path overshoot, in an interception turn (circle arc more or less deformed to allow for wind effect) in the horizontal plane. This graphic representation enables the pilot to see and act early enough to adjust his approach, then his interception turn. This results in a gain in terms of efficiency and availability because, in particular, it relieves the pilot of the need to release the controls.
In addition, thanks to the first means of indication, the pilot is given graphic information supplying him both with the real direction toward which the aircraft is moving and a first estimation of the ground speed vector module at which it is moving. In addition, this indication offers the advantage of being displayed close to a screen position used by the pilot a great deal during the pre-defined flight path interception/monitoring phase, i.e. said first symbol indicating the current position of the aircraft.
In an advantageous embodiment, said first means of display present the second means of indication on said display screen only:                if a segment of the flight path is in the direction of said first rectilinear section of first indication resources; and        if this segment is at a distance less than a predetermined distance with respect to said first rectilinear section,        
Thanks to said second means of indication, the pilot has synthetic graphic information giving him the future rectilinear interception flight path if he continues to fly with the same current ground speed vector (module and direction). As soon as the ground speed vector varies, said graphic information is updated in real time.
In addition, in an advantageous embodiment, said circle arc of the third means of indication includes a radius depending on the speed of the aircraft and/or the aircraft capacities. Furthermore, said circle arc may be deformed to allow for the intensity and direction of the wind.
Furthermore, in an advantageous embodiment,                if a flight path segment is in the direction of said second rectilinear section of the second indication resource;        if this segment is located at a distance less than a predetermined distance from said second rectilinear section; and        if the flight plan requirements make an interception maneuver possible.        
Thanks to the third indication resource, the pilot has synthetic graphic information supplying him with the future turn to be made to intercept with and align on the flight path if the aircraft continues to fly along the same ground speed vector (module and direction).
In one specific embodiment, said interception assistance device includes, in addition, second means for detecting an obstacle and the first means of display are liable to present, in addition, on said display screen, at least a second symbol illustrating the position of said obstacle in said horizontal plane.
This invention also concerns an on-board system for assistance with the interception and monitoring by an aircraft of a flight path segment located in a horizontal plane. According to the invention, said system is outstanding in that it includes:                an interception aid device as specified above; and        a flight path follow-up aid device.        
In addition, according to the invention, said flight path monitoring assistance device includes:                third means of determining:                    a lateral deviation of the aircraft from a segment of the flight path in the horizontal plane; and            lateral margins tolerated either side of said flight path segment in the horizontal plane; and                        second means of display liable to appear on the display screen:                    a fixed (immobile) lateral deviation scale;            a fourth means of effective lateral deviation indication corresponding to a straight line segment provided for on said scale and illustrating the effective lateral deviation of the aircraft from the flight path segment to be followed; and            a fifth means of indicating excessive lateral deviation appearing on said scale when the aircraft approaches at a predetermined distance, one of said lateral margins.                        
In an advantageous embodiment, the size of the fixed scale remains constant thanks to the automatic adjustment of the proportion between the real deviation and its representation on the display screen. Accordingly, whatever the aircraft flight phase, the fixed scale preserves the same size on the display screen.
In addition, in an advantageous embodiment:                said straight line segment of said fourth means of indication is inclinable; extraordinary; and/or        when said fourth means of indication reaches its stop, it changes form and remains at the stop; and/or        said fifth means of indication is flashing.        
To assist with the interception of a flight path including a multitude of segments, advantageously, said second means of display will also present on said display screen a sixth means of indicating a change in flight path segment to follow.
In addition, advantageously, said second means of display will present on said display screen a seventh means of indicating the lateral velocity tendency.
In a simplified and preferred embodiment, said first display resources for the device providing interception assistance and said second means of display of the second monitoring assistance device will be part of one and the same display unit.
Furthermore, the system in accordance with the invention will also include means of transmitting information liable to connect said first means of said interception aid device and said third means of said monitoring aid device to an acceptance autopilot for the transmission of information. Accordingly, all the data generated by the first and third means can be transmitted to an autopilot, which deals with automatic aircraft guidance.