FIELD:

The present invention relates to testing and validation by use of VIRTUAL TERRAIN of airborne systems providing terrain awareness by the use of stored terrain database.

BACKGROUND:

Ground Proximity Warning System (GPWS) and Terrain Awareness Warning System (TAWS) as the name suggests, are systems used on aircrafts to provide timely and necessary alerts to the crew of possible collision with terrain. The systems are aimed to provide necessary cautions and alerts to the aircraft crew to prevent Controlled Flight Into Terrain (CFIT) accidents.

With the ever increasing use of air transport for various applications, the need for operation of air services around the clock has increased. The same has resulted in flying different types of aircrafts under different conditions. With the need to provide continued air services, there is a need to fly the aircraft in different conditions irrespective of the climatic conditions and the ti,e of day.

The possibility of CFIT accidents greatly increases during Instrument Flight Rules (IFR) / Instrument Meteorological Conditions (IMC). Hence, the use of systems such as GPWS and TAWS become imperative.

As the systems are expected to provide necessary cautions and alerts in case of possible collision with terrains, the systems need work accurately and provide accurate alerts as the action initiated by the air crew is based on the alerts being provided by the system.

Considering these facts, it is necessary to ensure that the system be tested accurately with respect to their functionality.

As the system provides warnings on possible collision with terrains, it is necessary that the system be tested against the same. To test the system for generation of necessary alerts, the aircraft would have to be flown into a terrain. The same involves certain elements of risk considering the fact that there could be possible collision in case no warnings or incorrect warnings are generated.

Further, as the test involves validating certain envelopes of the system, the same is not accurately possible owing to the lack of a proper reference as the terrains are not of unique geometric shape.

Considering the above limitations/ restrictions, an innovative approach has been developed to accurately test and validate GPWS / TAWS for use on aircrafts. The approach utilizes the new concept of VIRTUAL TERRAIN in order to test the systems.

The testing and validation of GPWS on the Advanced Light Helicopter has been performed by use of the VIRTUAL TERRAIN concept.

SUMMARY:

The present invention is a VIRTUAL TERRAIN that is used for testing of airborne systems that provide terrain awareness by the use of stored terrain database. The VIRTUAL TERRAIN method consists of modifying the existing terrain database at any suitable location to create a virtual terrain of any desired characteristics. The advantage of using this approach is that it facilitates the accurate testing of the terrain awareness providing system due to the availability of a proper reference as the virtual terrain would be of a defined geometrical shape. The additional advantage of reduced risk of flying into terrain is provided by the system. The aircraft is flown around the area where the virtual terrain has been created. The existence of the virtual terrain is detected by the terrain awareness system and necessary alerts are generated by the system. The concept is advantageous since the airborne system is not capable of identifying or discriminating between actual terrain and virtual terrain. Hence, the entire validation of the system can be carried out without actually testing the system with a real terrain. Hence, all risk factors associated with testing and validating the system by flying into actual terrains is eliminated. Thus the invention facilitates accurate and safe testing of airborne terrain awareness systems.

DETAILED DESCRIPTION:

Conventional approaches of testing systems providing terrain awareness comprises of flying the aircraft towards actual terrain. The method would yield an approximate result regarding the envelopes defined for the system. As the system is to generate warnings on possible collision with terrains, it needs to be ensured that the warnings are generated at the correct time. When the term 'correct time' is used, it means that the time has to be determined with a base reference. Considering the fact that the contours of the earth are uneven and do not possess any identifiable geometric shape, the exact moment of impact is difficult to establish. This leads to an obscure reference. An ambiguous or in-deterministic reference will never let establish accurate results. This fact makes the testing and validation of terrain awareness systems difficult. Further, the safety aspect is compromised with while performing these tests as there is a possibility of collision with the terrain.

The invention of the VIRTUAL TERRAIN for the testing and validation of terrain awareness systems has ensured that the system be accurately tested with no possible safety concerns. Extensive simulations have helped in understanding the behavior of the system thus building necessary confidence for actual flight testing.

The use of traditional approach towards testing of the system involved high risk and would only provide an approximation to the actual behavior of the system. A full deterministic result cannot be obtained. Considering the same, innovative approaches have been adopted in the testing and validation of the system.

The invention of VIRTUAL TERRAIN has been used for testing and validation of the terrain awareness envelope defined in the Ground Proximity Warning System being used in the Advanced Light Helicopter (ALH) that is indigenously designed and manufactured by Hindustan Aeronautics Limited (HAL).

The GPWS on the ALH is a software module consisted of a predefined envelope. The envelope of the GPWS is as indicated in figure 1.
Figure 1. GPWS Envelope The GPW envelope consists of two portions, the Caution Envelope and the Warning Envelope. TERRAIN caution is indicated when the terrain is within the caution envelope and PULL UP warning is indicated when the terrain is within the warning envelope. Necessary aural alerts along with the visual indications are provided.

To validate the boundaries of the envelope, the helicopter is to be flown such that the terrain is around / within the boundary of the envelope. For defining any boundary, it is necessary to know the reference. The reference in the case of validating the system performance envelope is the terrain. Terrains are natural occurrences that are found in the world. Terrains are normally of varied and irregular shapes. The possibility of obtaining a terrain with an accurate geometrical shape is rather difficult and most probably impossible. As terrains are of irregular shapes, it is not possible to establish a standard reference to validate the boundaries of the system generating alerts.
The system consists of the elevation data that is pre-fed into the system memory. Based on the inputs received from the navigation systems, the GPWS detects for any terrain within the envelope indicated in figure 1. The envelope is defined aroung the present position of the helicopter. In case of any terrain within the envelope, necessary cautions or warnings are generated by the system.

The GPWS reads the terrain information that is pre-fed into the system. Active means are not utilized for detection of terrains. The necessary alerts and warnings are generated only based on the terrain database available in the system memory.

Hence, as the terrain awareness is based on the internal stored database, if the database is modified, the system would react to the modified data. This concept has been exploited by means of the present invention of the virtual terrain.
In the VIRTUAL TERRAIN invention, the terrain data is modified to create an imaginary terrain of any suitable size and dimensions. The invention facilitates the creation of terrains of proper geometric shapes. As the new created terrains are of proper geometric shapes, it becomes possible to validate the boundaries of the envelope due to the availability of a proper reference.

In the testing and validation of the GPW envelope onboard the ALH, the terrain data around a suitable location was modified to create a geometrically accurate rectangular terrain as indicated in figure 2.

The terrain was created by accessing the terrain database using suitable software and modifying the elevation values at the desired data points to create a terrain of proper geometric shape.
Figure 2 indicates the virtual terrain obtained after modification of the terrain data.

Figure 2. Virtual Terrain
Since, the reference is now available, accurate testing can now be carried out to validate the system.

CONCLUSION:

With the successful testing and validation of the system, the approach can be used on any airborne platforms. The methodology is not aircraft specific, i.e. it is not limited to the use on helicopters. The approach would find wide acceptance for high speed aircrafts (both military and civil) where the need for accuracy is compounded by the fact that the reaction time is limited. Hence an accurate system would be useful.

Thus, the following challenges have been overcome by the use of VIRTUAL TERRAIN:

a) Safety of Helicopter and Pilots.

b) Validation of the terrain awareness system functional envelope.

c) Establishment of reference to validate the Envelope.

d) Validation of accuracy of warnings.

e) Building Confidence for Flight testing in actual terrain environment.

With the present regulations, the need for a terrain warning system has been mandated by the Civil Regulatory Authorities (DGCA) in India.

Hence, there is a need for installing a terrain warning system on all civil helicopters. This invention of the VIRTUAL TERRAIN would facilitate the accurate testing of terrain awareness systems so as to ensure satisfactory performance.

Signature of Inventor Signature of Applicant
Page 5 of 6 Having thus described the basic concept of the invention of the VIRTUAL TERRAIN, it will be rather apparent to those skilled in the art that the foregoing detailed disclosure is intended to be presented by way of example only, and is not limiting. Various alterations, improvements and modifications may occur and are intended to those skilled in the art, though not expressly stated herein. These modifications and improvements are intended to be suggested hereby, and are within the spirit and scope of the invention. Additionally, the recited order of processing elements or sequences, or the use of numbers, letters, or other designations therefore, is not intended to limit the claimed process to any order except as may be specified in the claims. Accordingly, the invention is limited only by the following claims and equivalents thereto.

CLAIMS:

1. Creation of VIRTUAL TERRAIN.

In the VIRTUAL TERRAIN invention, the terrain data is modified to create an imaginary terrain of any suitable size and dimensions. As the new created terrains are of proper geometric shapes, it becomes possible to accurately validate the boundaries of the envelope and the cautions and warnings generated by the GPWS due to the availability of a proper reference.

The invention of the virtual terrain concept provides a means of accurately testing the functionalities of systems. The invention provides a means of testing and validating the systems by eliminating substantial risks involved with respect to air crew safety. As the virtual terrain invention is based on the modification of the terrain database that is used in the systems, the invention is applicable to different types of terrain database and does not pose any restriction on the use of the method for any particular terrain database.

The term VIRTUAL TERRAIN is synonymous with terms such as ARTIFICIAL TERRAIN, MODIFED DIGITAL TERRAIN, COMPUTER GENERATED TERRAIN, etc. and represents any terrain that has been created or modified and is not an actual terrain that exists in any geographical location of the world.

2. Testing and validation of GPWS / TAWS using VIRTUAL TERRAIN.

The system functionality is checked by flying the aircraft into the terrain. The aircraft may be simulated or/and actual flight may be carried out. Flights are performed along different paths with different offsets. The offsets help in validation of the side envelopes of the system.

Flights are also performed at different altitudes and speeds to verify the forward envelope. In case cautions and warnings are generated due to possible collision with terrain, corrective actions are performed to test the functionality of the system with respect to proper termination of warnings and spurious warnings.

The testing and validation of the GPWS system comprises of testing the system by means of:

a) Flight simulations using VIRTUAL TERRAIN.

b) Flight testing using VIRTUAL TERRAIN and

c) Flight testing using actual terrain.