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New aircraft types are accelerating the need for new navigation technology. Tiltrotors will clearly become a major part of both the civil and military aviation infrastructures. To reach their potential, tiltrotors and conventional helicopters must be allowed to make full use of their maneuverability and point to point capabilities in all weather conditions. They must not be restricted to using the same methods that were developed for fixed-wing aircraft many decades ago.

Digital Design Ltd. has been engaged in research and development in three separate areas of advanced navigation, and on how these areas can be combined together into one integrated system.

The major advantage of the tunnel concept is that it allows precision approaches to be made by GPS equipped aircraft without the need for ground based navaids. In addition the flight path may be curved, and may contain variations in gradient.

Research has proven the practicality of this concept for precision approaches, and its benefits to safety by increasing the situational awareness of pilots.

The concept of a navigation tolerance area is fundamental to IFR navigation. It is considered to be the area around the nominal flight track in which the aircraft can be expected to be found. This area must take into account the accuracy of the navigation equipment in use, and how accurately a pilot is able to fly to that equipment.

Obstacles and terrain within this navigation tolerance area are examined to determine what altitudes aircraft must fly at to maintain a safe margin of terrain clearance.

Traditional navigation aids and equipment have their tolerances defined angularly. This results in a splayed navigation tolerance area, covering a larger area at a greater distance from the navaid site. GPS on the other hand can be considered to have a fixed navigation tolerance, defined as the maximum error when used in either a differential or non- differential mode. This results in the sides of the navigation tolerance area being parallel to the nominal track.

Digital Design Ltd. has formalized and expanded these concepts in our definition of a 'navigation channel'.

A navigation channel is a theoretical channel in space through which the aircraft is expected to fly. The main difference over existing concepts is that the path of the channel can be computed dynamically in flight - it can curve around obstacles, descend into airports or vertiports, and climb out on departures. It is particularly suited to the higher maneuverability of helicopters and tiltrotors.

Navigation Channels allow curved approaches to be flown with relative ease. The missed approach channel can be seen in the background.

The path of the channel is automatically calculated prior to each phase of flight, and is determined by the aircraft's performance characteristics, the positions of all ground based obstacles, the prevailing wind, and the position of the navigation channels used by other aircraft in the vicinity.

The navigation channel itself consists of two separate channels. An outer obstacle clearance channel and an inner guidance channel.

Structure of the Navigation Channel

The obstacle clearance channel determines the area that must be free of obstacles. It is expected to contain the aircraft at all times. This channel exists for the purposes of calculating the path of the navigation channel. It is not normally displayed to the pilot.

The dimensions of the obstacle clearance channel differ for the different phases of flight, as a result of different accuracies in navigation, different airspeeds, and aircraft configurations. Typically we are working to a channel width of 500 m for enroute navigation using standard GPS, and a channel width of 100 m for precision approaches using differential GPS.

The guidance channel exists purely as a visual aid to the pilot, and is used to produce the 3D representation of the aircraft's position relative to the required track. It is smaller than the obstacle clearance channel - its size is set by how well a pilot can respond to out of position indications for different phases of flight.

	Too High
Too Far Left	Correct Position	Too Far Right
	Too Low

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