Aircraft Systems 3, Section Terrain Awareness Warning System - TAWS

PURPOSE OF TAWS

- To give visual and aural warnings to help prevent accidents caused by controlled flight into terrain

- TAWS is the generic name for the onboard system aimed at preventing controlled flight into terrain.

- Specific systems currently used are GPWS and EGPWS (Effectively brand names)

- EGPWS is more like a predictive GPWS

ELEMENTS TAW Central Processing Unit -

TAWS INPUTS -

- RADALT

- ASI/MACH

- GPS

- ADC(VSI/ALT)

- Glidepath deviation

- U/C position

- Flap position

TAWS OUTPUTS

- Master warning

- ECAM/EICAS

- Aural warning

- Navigation Displays

OPERATING PRINCIPLE

- Using the inputs from the previous slide TAWS:

- Computes closure with terrain

- Terrain based on data base of know obstacles (AIRAC - Aeronautical Information Regulation and Control)

- Compares with acceptable values for configuration of aircraft and Mode of TAWS

TAWS Types B

Class B TAWS - No looking forward terrain data

- Reduced required terrain clearance

- Imminent terrain impact

- Premature descent

- Excessive rates of descent

- Negative climb or altitude loss after take off

- Descent of aircraft below 500ft above terrain - callouts

- Optional - may provide terrain awareness display

TAWS Types A

Class A TAWS - Used Terrain Data, GNSS, and includes all the requirements of Class B TAWS

- Excessive Closure rate to terrain alert

- Closure into terrain when not in landing config

- Excessive downward deviation from ILS Glideslope

- Required: Display that shows terrain awareness or obstacles

TAWS Class A - GPWS

- Monitors 7 basic modes

- Mode 3 & 4 automatically selected modes

- Crew reactions to alerts IAW SOP's as no correction advisor is given on PFD/ADI

- Failure automatically indicated on PFD/ADI/CAS

Class A TAWS/GPWS MODES

Mode 1 - Excessive Rates of Descent

Mode 2 - with respects to rising terrain.....

Mode 2A - Excessive Terrain Closure when not in approach config

Mode 2B - Rising Terrain when in approach config

Mode 3 - Negative Climb Rate or Altitude Loss After Take Off

Mode 4 - Flight into Terrain when not in Landing Config

Mode 4A - Too low - Gear up

Mode 4B - Too low - Flaps up

Mode 5 - Excessive Downward deviation from ILS approach, I.E. Glideslope

Mode 6 - Below Minimums (E.G. "Five Hundred") and bank angle

Mode 7 - Reactive Windshear Alerts

WARNING MODES

Alerts require crew to correct flight path or configuration - Soft Warning - Sink Rate

Warnings requires immediate action - Hard Warning - Pull Up

Electronic Flight Information Systems - DISPLAY OF TAWS/EGPWS -

- Pictorial representation of terrain & obstacles dependant on individual installations

Typically uses:

- Black for safe clearance 1000' plus

- Yellow for caution 100' to 1000'

- Red for warning less than 100'

EGPWS and EHSI Moving Map

Enhanced Ground Proximity Warning System - EGPWS is more predictive, uses nav data base and the GNSS system to provide warning of possible impact to the ground well before the first generation GPWS would respond.

Some functions of a generic moving map system:

- Obstacle Warning Functionality

- Obstacles that can issue warnings

- High Bridges, Towers, Power Lines, Chimneys, etc.

- Terrain collision warning

- Elevation Mode

MODE 7 - WINDSHEAR DETECTION - Reactive

- Compares rate of change of ground speed with rate of change of airspeed

- Shear illuminates Red Light

- Aural warning - (WINDSHEAR X 3)

WINDSHEAR - OPERATION -

- Operates through MFD/PFDs

- Inputs from INS/GPS (Ground speed)

- Inputs from ADU - ASI, VSI & AoA

- Inputs from RAD ALT

- Includes FAIL annunciator if INOP

MODE 7 - Windshear Reactive and Predictive

- The previous four slides have covered Reactive Windshear. Tells you when you've found yourself in it

- Predictive Windshear Warning Systems (PWS) provides Alerts of windshear condition detected ahead of the aircraft

Looking forward the aircraft uses:

- Weather Radar to pick up the doppler shift of particles

- When combined with other aircraft systems it provides warnings and guidance recovery action. - Displayed on the PFD/ADI and aural system

LIDAR - Laser Imaging, Detection, And Ranging - Laser Doppler Radar

- Ground based LIDAR (Infrared Laser) equipment can transmit windshear information to the aircraft through the ACARS system to inform the aircrew.

- LIDAR Measures the doppler shift of particles around the airfield

- Once the information is received by the aircrew will assess it in combination their own onboard information