The Runway Awareness and Advisory System (RAAS) is one of a number of related software enhancements available on later-model Enhanced Ground Proximity Warning Systems. RAAS is designed to improve flight crew situational awareness, thereby reducing the risks of runway incursion, runway confusion and runway excursions.
Runway Awareness and Advisory System uses airport data stored in the EGPWS database, coupled with GPS and other onboard sensors, to monitor the movement of an aircraft around the airport. It provides visual/aural annunciations at critical points, such as "Approaching Runway 09 Left and confirmation when an aircraft is lined up on the runway prior to takeoff: for example, "On Runway 09 Right, 2,450 metres remaining." In a scenario where a crew inadvertently lines up on a parallel taxiway and commences a take off, an aural alert “On Taxiway, On Taxiway” is provided if the aircraft speed exceeds 40 kts. On approach and after touchdown, the system continues to announce the distance to go until the end of the runway is reached.
Advisories/cautions are generated based upon the current aircraft position as compared to the location of the airport runways, which are stored within the EGPWS Runway Database.
The aurals can be grouped into two categories:
RAAS provides the flight crew with five ‘routine advisories'. Three of these annunciations will be heard by the crew in normal operations, providing increased position awareness relative to the runway during taxi and flight operations. They are intended to reduce the risk of a runway incursion. The two remaining ‘routine’ advisories provide information about the aircraft location along the runway, and are intended to reduce the risk of overruns. The five advisories are:
In addition, RAAS provides the flight crew with several ‘non-routine’ advisories/cautions. These annunciations are designed to enhance safety and situational awareness in specific situations not routinely encountered during normal aircraft operations. Some of the RAAS advisories include distance information. The unit of measure used for distance can be configured to be either metres or feet.
Each RAAS function is independently enabled based on a customer specification and, when enabled, the RAAS functions operate automatically without any action required from the flight crew.
In addition to the aural annunciations provided, visual caution indications may be activated if the appropriate criteria are met. Visual text annunciations can also be configured so they are overlaid on the terrain display for a period of time after the warning is generated.