1 PILOT'S GUIDE . Terrain Awareness and Warning Systems TAWS. Buyer's GUIDE B Y P A U L N O V A C E K See TAWS COMPARISONS CHART on pages 36, 37 & 39. C. ontrolled Flight Into Terrain These Terrain depiction systems TAWS computer also receives (CFIT) describes an acci- show the Terrain in color codes aircraft configuration and air-data dent where a completely just as sectional charts. The col- information to then create a 4-D. airworthy aircraft is flown into ors depict elevations above sea position of latitude, longitude, alti- the Terrain . These accidents only level and it s up to the pilot to tude and time. It then compares occur during poor visual condi- determine if sufficient clearance this position with the on-board tions; but other factors besides exists. A little bit of mental gym- database of Terrain , obstacles visibility usually contribute, such nastics are required to correctly and runways to determine any as a cockpit distraction, malfunc- interpret these moving maps.
2 Conflicts. If the TAWS com- tioning equipment, an ATC error The Terrain mapping systems are puter detects a possible conflict or a pilot/controller miscommuni- only capable of giving the pilot between the future flight path cation. To reduce the occurrence the general Awareness of the ter- of the aircraft and Terrain , visual of Controlled Flight Into Terrain rain, no audio or visual warnings and audible warnings are given accidents, Terrain Awareness are given. to the pilot. and Warning Systems (TAWS) A true TAWS system on the were developed to provide a other hand, can look ahead of Class-A TAWS. Warning of a possible Terrain con- the aircraft and warn the pilot For those airplanes that flict. The purpose of a TAWS is of impending impact with the require Class-A TAWS, the sys- to provide a Warning with enough ground; thus monitoring the tems include a minimum of five time for the flight crew to take pilot s actions and providing an basic functions: appropriate action.
3 Audible and visual alert if the air- 1. Forward looking Terrain There are various types of craft is about to have a date with avoidance TAWS systems, whether they fall the ground. Hopefully, the pilot This function looks ahead and into the definition of TAWS or not. of a TAWS-equipped aircraft will below the aircraft flight path to The three general categories pro- never hear a Terrain or obstacle provide a suitable alert if a poten- vide increasing levels of protec- Warning , but the safety margins tial threat exists. tion from the basic Terrain Map are there just in case. 2. Premature descent alert to TAWS-B through the highest The TAWS computer receives This function uses the predict- level of protection TAWS-A. position information from a GPS ed flight path information (deter- Many moving maps contain receiver, and compares that mined from an approach naviga- databases of Terrain elevations position with the internal ter- tion source) and its own airport gained from government charts.
4 Rain or obstacle database. The database to determine if the aircraft is below the normal (typi- Federal Aviation Regulations Require: cally 3 degree) approach path for TAWS Class-A equipment is required for turbine-powered airplanes operated the nearest runway. If a conflict is under part 121 (airline) and part 135 (charter) of 10 or more passenger seats. detected, a Warning is given. TAWS Class-B equipment is required for turbine-powered airplanes operated 3. Attention alerts under part 91 with six or more passenger seats and for turbine-powered airplanes The system provides appropri- operated under part 135 with six to nine passenger seats. ate visual and audio alerts for - 34 - both cautions and warnings . 4. Indications of imminent tion airplanes to the largest air 4.
5 Terrain Awareness display contact with the ground transports. They even have two The TAWS equipment provides The TAWS equipment provides models specifically designed for Terrain information to a suitable indications of possible Terrain the special needs of helicopters, display system radar or multi- conflicts for the following condi- who routinely fly eye-level with function display. tions: the obstacles they re trying to 5. Indications of imminent Excessive rates of descent avoid. contact with the ground Negative climb rate or alti- The TAWS-A Mark series The TAWS equipment provides tude loss after takeoff (Mark V-VIII) of EGPWS are indications of possible Terrain Voice callout five hundred intended for corporate jet and conflicts for the following condi- when the aircraft descends to air transport installations.
6 As an tions: 500 feet above the Terrain or option, they contain software Excessive rates of descent nearest runway elevation to detect windshear conditions Excessive closure rate to Terrain and alert the flight crew when Negative climb rate or altitude NOTE: A Class-B TAWS instal- to take evasive maneuvers to loss after takeoff lation does not require a Terrain escape a microburst. A recent Flight into Terrain when not in display (as does Class-A), but addition to the Mark series is landing configuration the Awareness of Terrain around the software upgrade for RAAS, Excessive downward deviation the aircraft is severely lacking. Honeywell s Runway Awareness from an ILS glideslope The TAWS equipment is either and Advisory System. The field- Voice callout five hundred, contained in a remote avionics updatable software enhancement when the aircraft descends to box that feeds a multi-function uses GPS position data and the 500 feet above the Terrain or display, or contained entirely in EGPWS database to provide nearest runway elevation the display unit.
7 The larger air- audio advisories that supplement craft generally use the remote flight crew Awareness of position Class-B TAWS box configuration, while the during ground operations and on For those aircraft that require smaller aircraft use combined approach to landing. Honeywell Class-B TAWS, the systems units. The following are short is the only TAWS manufacturer include a minimum of four basic descriptions of each TAWS man- offering this enhanced safety functions: ufacturer. The comparison chart feature. 1. Forward looking Terrain that accompanies this article lists The Mark XXI (TAWS-B) and avoidance the particulars of each TAWS Mark XXII (TAWS-A) offer ter- This function looks ahead and unit. rain Awareness functions tailored below the aircraft flight path to uniquely to helicopter flight pro- provide a suitable alert if a poten- Honeywell files.
8 For the light jet, turboprop tial threat exists. Honeywell s EGPWS, or and piston crowd, Honeywell s 2. Premature descent alert Enhanced Ground Proximity general aviation line of EGPWS. This function uses the pre- Warning System, was the pio- offer TAWS-B Awareness and dicted flight path information neer TAWS system that com- alerting of potential Terrain or (determined from an approach bined an exhaustive Terrain and obstacles. The EGPWS is even navigation source) and its own obstacle database with the tra- bundled with traffic alerting sen- airport database to determine if ditional Ground-Prox systems to sors, either TAS or TCAS-I, the aircraft is below the normal offer look-ahead alerting. There to provide total Awareness of (typically 3 degree) approach are 10 EGPWS systems cur- ground-based and air-based path for the nearest runway.
9 If a rently available from Honeywell threats. conflict is detected, a Warning is that can be installed as remote Even though the mandated given to the pilot. computers in over 250 types of TAWS-B installations don t 3. Attention alerts aircraft. Since the EGPWS was require a cockpit display, the The system provides appropri- first introduced, 30,000 have graphic depiction of Terrain sur- ate visual and audio alerts for been installed in aircraft ranging rounding the aircraft greatly both cautions and warnings . in size from small general avia- Continued on page 38 . - 35 - TAWS COMPARISONS. TAWS REMOTE COMPUTERS. Model Description Price Honeywell , TAWS-A, w/windshear detection, vertical situation $74,710 without internal GPS. EGPWS display (VSD), radar AutoTilt T, worldwide Terrain /Ob- $77,630 w/internal GPS.
10 Mark V stacle/Airport database, optional RAAS. RAAS add $18,932. Remote Computer - Digital Interface TAWS-A, w/windshear detection, vertical situation $74,710 without internal GPS. EGPWS . display (VSD), radar AutoTilt T, worldwide database, $77,630 w/internal GPS. Mark VII. optional RAAS. Remote Computer - Analog Interface RAAS add $18,932. TAWS-A, regional Terrain /Obstacle/Airport databases. EGPWS $26,168 without internal GPS. Remote Computer designed for Turboprop aircraft Mark VI $28,358 w/internal GPS. - Limited Analog/Digital Interfaces TAWS-A, worldwide Terrain /Obstacle/Airport database. EGPWS $39,358 without internal GPS. Remote Computer designed for Turbofan and Turbo- Mark VIII $40,402 w/internal GPS. prop aircraft - Limited Analog/Digital Interfaces EGPWS TAWS-A, w/internal GPS, regional Terrain /Obstacle/.