The main task of the vast majority of equipment installed in the cabin of the Aircraft is to provide awareness of the pilot about the position of Aircraft relative to the earth's surface. In addition, a special influence on the safety of air transportation have factors associated with deterioration of visual visibility in conditions of flight operations at night and in adverse meteorological conditions. Limitations of visual visibility is the most critical factor affecting flight operations and safety. Sad statistics shows that about 30% of fatal accidents happen on the means of private aviation resulting in collision with the earth's surface or artificial obstacles because of reducing visual visibility. Reduction of visual visibility is one of the biggest factors causing delay or cancellation of flight, and as a result leads to losses for the airlines.
One of the first , who tried to solve the problems caused by the lack of visibility, were the members of NASA staff, suggesting a synthetic vision system [88].
Synthetic Vision System (SVS) - is a system of displaying information that provides a virtual representation of the real external environment, combined with the information necessary for piloting and navigation of the Aircraft. The SVS system is based on accurate three-dimensional map of the terrain on a global scale, combined with three-dimensional artificial obstacles, which are stored in digital form in the onboard database. Such systems create or ‘synthesize’ the image of the surrounding terrain and artificial obstacles without meteorological and timely (caused by twilight) impact and reflect it to the pilot via the EFIS or HUD. Thus, SVS provides the pilot with a "perfect" reflection of the environment, indicating the objects that are obstacles for piloting [46; 51; 68].
The SVS system is based on determining the precise location of Aircraft using the navigation aids with subsequent reflection of the underlying terrain, which corresponds to the visible area from the point of Aircraft’s position. The location of the Aircraft is determined using the joint estimation of data from GNSS and functional additions WAAS or EGNOS, radio altimeter, VOR/DME and inertial navigation systems. This combination of sources coordinate information provides the location of the Aircraft with the highest accuracy. In accordance to it, the correct functioning of SVS needs a capable network of ground stations of differential corrections such as WAAS or EGNOS.
In addition, SVS- is an effective medium to display all necessary navigation information to the pilot . With special markings data from ADS-B and TCAS traffic is displayed, specify the planned route of flight and other useful information (Fig. 154).
Fig.154 General structure of SVS
Regardless of the type of Aircraft, SVS is an effective means of improving the safety of aviation operations. Accordingly to the class of Aircraft on which SVS is set, there are many different concepts of its construction. In concept, developed by NASA, the main elements of the SVS must be such [96]
- Sensors and databases of the SVS:
- on-board database of synthetic vision;
- radio altimeter;
- onboard meteoradar;
- on-board radar of millimeter wave band;
- Board system of infrared vision.
- SVS displays:
- primary flight display (PFD)
- navigation display (ND)
- other Aircraft displays
- Head-Up Display (HUD) or Helmet-Mounted Display
- Calculators of SVS:
- Synthesizing of image:
- The evaluation of input data and their comparison with accepted values, assessment errors;
- evaluation of natural inputs and their integration;
- risk assessment;
- synthesize the input data;
- building of the required images of the earth's surface;
- Checking oferrors existence and signaling about their presence;
- grouping, verifying the truth and the approval of results of system operation:
- evaluation of the relevance of existing databases and their inherent errors.
- evaluation of the appropriateness of the use of information sources;
- issue an appropriate warning message of the system;
- check for errors and alarm about their presence
- Display of marks:
- actual and planned trajectories of the Aircraft;
- Dangerous for piloting elements;
- monitoring system for the runway;
- Aircraft maintenance at low altitude and landing;
- navigation and dangerous elements;
- hazardous situations;
- general symbols.
- Synthesizing of image:
- Equipment:
- necessary for operation of the SVS equipment;
- channels of information exchange with other Aircraft systems.
- Other Aircraft systems :
- GNSS;
- IRU or AHRS;
- air signals;
- landing system;
- equipment communication and data exchange;
- TCAS;
- ADS-B;
- TAWS;
- laser altimeter.
The generalized principle of the SVS concept NASA shown in Fig. 155.
Fig. 155. The principle of construction SVS
The principle of operation of the SVS based on the operation information from various databases. The reliability of the information provided by SVS depends on the relevance of on-board databases. That is why SVS requires continuous updating of internal databases.