**6. Terrain awareness and warning system**

Terrain awareness and warning system (TAWS) is a piece of airborne safety equipment designed to provide a warning on terrain collision to the pilot reliably and automatically [10]. Ground proximity warning system (GPWS) is the universally accepted system and developed from TAWS [15, 16].

TAWS provides proper warning about the upcoming obstacles and terrains by using terrain database and GPS positioning. Since TAWS depend on terrain database and GPS positioning, it gives a prediction based upon projected location and aircraft location. The system warns pilots by providing both voice and visual intimations. The pilot takes action according to the warning received from TAWS [11, 12]. The system is time-dependent, and therefore it reimburses the performance of aircraft and speed. TAWS and GPWS are not same because TAWS produces warning signals based on the aircraft's real position (indicated by built-in GPS) concerning a terrain map installed in the equipment whereas GPWS produces warnings only through the inputs received from the radio altimeter [15, 16].

TAWS works by using the instrumental values (like inbuilt GPS) and digital elevation data- of the aircraft to know the future position, which interconnects the ground. So the pilot intimated through audio warning and visual warning about the upcoming terrain well in advance. **Figure 5** shows the typical TAWS (right side). The image, which displayed in the left side, shows different colors for the respective altitude rate from sea level by reference- altitude [10–12].

#### **6.1. There are mainly three classes in the terrain awareness and warning system-**

They are TAWS class A, TAWS class B and TAWS class C.

**TAWS Class A** provides the following features:


**Figure 5.** Terrain awareness and warning system.


**TAWS Class B** equipment provides the following:


#### **6.2. Modes of operation**

The various sets of hazardous conditions that the GPWS monitors and provides alerts for commonly referred to as modes. These described in detail in the following paragraphs. Hazard awareness provided by TAWS aural alerts or warnings and illumination of alert and warning lights in response to different situations. **Table 1** shown below illustrates a typical TAWS system mode of the operation of flight, respectively.-

#### **6.3. Response to a TAWS activation**

TAWS is a safety system, which provides two different warning when aircraft approaches terrain namely soft warning and hard warning. Soft warning indicates an unusual status with respect to terrain location that needs immediate attention and a change in aircraft configuration or flight path. On the other hand, hard warning indicates an unsafe situation, which needs immediate action. TAWS response procedures appropriately designed by operator based on the flight type and performance [13, 14].

#### **6.4. Problem description**

MATLAB program for the TAWS mode and its descriptions presented in this chapter. The "**Excessive terrain closure rate**" determination for **mode 2** programmed and simulated. The program created by using altitude-measuring formula by considering arbitrary pressure values for the various altitude

$$Z = \left(\frac{-RT}{gM}\right) \ln P\_0 - \ln P \tag{1}$$

where Z—height from the ground, RT—gas constant temperature, g—gravity, P0 —random pressure value, P—sea level pressure, respectively.-

The ultimate aim of the program is to fly the aircraft in the well-defined path without collision. For example, for the mode operation set the "z" value for some extent. When it detects some obstacles, i.e., in excessive terrain closure rate, it will show "**TERRAINTERRAIN**" "**PULL UP**" message and when it comes to normal steady flight shows "**NO WARNING**" message.-


**Table 1.** The modes of operation in TAWS [17].
