TAWs for Terrain

If you fly a six-seat turbine, the FAA says terrain gear is a must-have. The good news: the mandate means non-certified systems are capable and affordable.

by Larry Anglisano

Well cut right to the chase and explain the expensive FAA mandate: by March 29, 2005 all turbine-powered aircraft with six or more passenger seats must have forward-looking terrain awareness (FLTA) gear otherwise known as TAWS for terrain awareness and warning system. In a nutshell, its supposed to reduce the number of controlled flight into terrain accidents.

TAWS comes in two categories: Class A TAWS, which requires a terrain display and Class B TAWS, which is terrain warning via voice call-outs. While these regulations may be out of the spectrum for many owners, its important to understand that for even Part 91 operators of small-turbine aircraft, TAWS is going to be a fact of life.

If you own a King Air, Conquest or Caravan, to name a few, legal-TAWS gear will be on your must-buy list. The regs say that Part 91 aircraft configured with six or more passenger seats must be equipped with Class B TAWS. More seats and higher ops specs require more stringent TAWS compliance, as Part 135 and Part 121 operators already know.

The FAA announced this mandate about five years ago, so there has been plenty of time to prepare. While many of our readers don’t operate turbine aircraft, terrain awareness gear-even the most basic systems-isn’t a bad idea. And that fact that the FAA has mandated this technology means that there have been cheaper, uncertified versions for owners who want the technology but don’t need or want to pay the price for certified systems.

Some operators, however, do equip their airplanes with legal TAWS systems for the sake of safety and we say more power to them, if they can afford it. In this article, we we’ll offer a round up of popular market offerings for terrain alerting gear, both for legal TAWS and for basic situational awareness.

Weve omitted the top-end heavy iron systems and also primary flight displays; the focus here is retrofits, either adding an MFD to a basic single-engine airplane or loading full-boat TAWS to your King Air or Citation.

Waiting for Garmin
Garmin GNS430 and GNS530 owners have lots of questions and the most frequent is: When the heck is my unit going to display terrain data like other MFDs? For some time, Garmin has promised this feature and the latest official word is that a TAWS-legal interface for the GNS530 units will appear on October 18, 2004, cutting it close for folks getting geared up for legal TAWS compliance.

The internal-to-the-box Class B TAWS feature has an introductory price of $6495 and must be completed at the factory. A non-certified terrain awareness upgrade for GNS430 and GNS530 units is expected in early November for $500, according to Garmin.

We think that both the legal TAWS and terrain advisory feature upgrades are bargain priced and for this reason, owners might consider the wait worth it. There are lots of GNS430s and the terrain alerting upgrade is sure to create a backlog at the Garmin factory.

In any case, the upgrade of an GNS530s to TAWS standards could be the most cost-effective way to add TAWS-compliant capability to smaller airplanes, especially ones already equipped with GNS530s.

We buy color MFDs partly to take advantage of detailed topographical data. Terrain and obstruction information tops the list of required features and overlaying the aircrafts flight profile over color-contoured terrain calms an otherwise rapid heartbeat on unfamiliar departures and arrivals in low weather, even if it stops short of providing true TAWS protection in the eyes of the FAA.

The now-Garmin AT MX20 MFD (and L-3 Communications marketed i-link MFD) was a hit right from the start as its 65,536-color high-resolution display seems perfect for playing a built-in terrain elevation database. This database color codes terrain in relation to the aircraft, alerting the user in true color to rising terrain.

We especially like the vertical profile view of terrain peaks and obstructions that are relative to the actual flight path of the airplane. Obstructions over 250-feet high are retrieved from the database and presented as tower symbology on the units basemap. Catenary support structures for overhead transmission lines are depicted, too.

The only snag in the MX20 terrain feature comes at installation. Since the terrain and obstacle-alerting feature of the MX20 and i-link require serial altitude input, an altitude converter is often a required piece of gear if the aircraft has a gray-code altitude encoder. While the common gray code encoder outputs in 100-foot increments, a more accurate serial encoder outputs in 10-foot increments and offers the box a more accurate input of actual aircraft altitude. If you don’t input altitude data to the MX20, the terrain function simply wont work.

In short, the MX20 is a well-rounded MFD and while its stock internal terrain function doesnt meet TAWS-legal specs, it does offer enhanced situational awareness with the ability show split-screen data including vertical profile terrain, IFR and VFR charts and traffic alerting. The MX20 I/O version (radar version) is what is needed to play TAWS terrain, not a base MX20 (unless you want to only use the advisory terrain base map).

The Avidyne FlightMax EX500 MFD might be the most versatile display available for the widest variety of airplanes. Its basic terrain functions include a built-in terrain base map –one of several pilot selectable base maps–and a North American database that includes towers and man-made obstacles higher than 200 feet.

The MSL-altitude labeled obstructions are overlaid on the 65,535-color display and a terrain scale depicts the highest terrain and obstruction height for a given area on the map. We recall once flying with a brave soul who decided to cancel IFR while still IMC. He blundered along VFR to his non-approach equipped strip, only to find the airplane popping in and out of the clag at low altitude. As we wondered what towers our gear doors were scrapping, using the Avidyne nearest obstacle function would have alerted us of the height and proximity of the nearest towers lurking below-and there were plenty.

Proof that the EX500 is suitable for airplanes small and large is the amount of available and approved external terrain inputs. In addition to the self-contained advisory terrain awareness, the unit has the ability to play a wide variety of existing terrain systems and new TAWS-legal interfaces. These include Bendix/King KGP560 general aviation EGPWS, the EGPWS MK V, VI, VII, VIII, XXI, XXLL and KMH880 IHAS. For this reason, the EX500 could be equally at home in a Part 91 owner-flown King Air or a Part 121 regional airliner.

King is King
Honeywell Bendix/King has perhaps the widest variety of terrain-depicting devices, from basic VFR-only map displays containing terrain contouring to TAWS-compliant systems suitable for airliners. At the bottom of the food chain is the low-cost color KMD150 MFD, which has basic terrain awareness via color contouring on the base map.

Digital terrain elevation data published by the National Imaging and Mapping Agency is internal to the units database and the result is reasonable terrain awareness for the VFR pilot seeking simple terrain contouring with towers overlaid on the base map.

The KMD250, a mini-color MFD unit (see Aviation Consumer, January 2004) thats part of the IHAS Integrated Hazard Awareness System, has the ability to play TAWS-legal remote terrain from the KGP560 EGPWS system that we’ll detail shortly.

Without the KGP560 input, the KMD250 has a relative terrain map with a similar look to an EGPWS presentation, with topo and obstruction data color coded relative to the aircraft present altitude. The terrain function uses input from an altitude encoder, a remote GPS altitude or baro-corrected altitude.

As we found during our previous review, the KMD250 is a full-featured MFD with a chassis size making it appropriate for airplanes large and small and with the KGP560 EGPWS input, it can be part of an economical legal-TAWS system. The larger KMD540-part of the IHAS 5000 and 8000 systems–display will also accept KGP560 input as we’ll as replace the Honeywell RDR2000 radar indicator.

Baby Ground Prox
Honeywell Bendix/King was the first to offer a TAWS product suitable for smaller airplanes with the KGP560 GA-EGPWS, a general aviation Enhanced Ground Proximity Warning System. The KGP560 contains a lot of trickle-down technology from the air transport line of EGPWS equipment, to which Honeywell is hardly a newcomer.

For years, the MK-series systems were the standard for corporate and air transport category airplanes and the baby ground prox follows this lead with modern technology that exceeds the Class B TAWS specification. The KGP560 (see May 2001 Aviation Consumer) uses a single remote processor that incorporates a built-in GPS receiver and a terrain/obstacle database.

Using look-ahead algorithms in conjunction with the terrain/obstacle database, the KGP560 outputs in six-colors to a display such as the KMD540 and KMD250 we mention above plus some Bendix/King radar displays. The system also provides audio outputs for 500-foot altitude callouts, excessive rate of descent, negative climb situations and premature descents.

The KMH880 is a combination traffic/terrain alerting system and contains the KGP560 processor as we’ll as the Honeywell traffic module all in one box. For light jets and such, the Honeywell KGP860 offers similar performance as the KGP560 but offers bank angle alerting and more options for displaying on EFIS systems that could be found in some of those jets.

L-3 Avionics Systems
High-end manufacturer L-3 Avionics Systems was initially off to a slow start with the Landmark TAWS8000 product, a legal TAWS Class B system. The Landmark 8000 is a remote processor that uses predictive warning functions from GPS data and its internal terrain/obstacle database. It includes terrain data for runways 2000 feet and longer.

The system, which exceeds Class B TAWS requirements, uses aural and visual warnings, displayed on the i-link MFD as we’ll as a variety of EFIS and radar displays. Like the Honeywell KGP560, the Landmark is suitable for smaller airplanes as it weighs less than 4 pounds and offers terrain avoidance features exceeding the Class B specification. Negative climb rate alerts, excessive descent rate alerts, descending-to-500-feet aural alerts and premature descent alerts are examples of some of these features.

As we go to press, the Landmark 8100 product is being introduced. It streamlines the installation process with all stand-alone system components, including its own WAAS-enabled GPS receiver. This eliminates the need for tapping into existing aircraft systems for positional and air data reference.

The 8100 also has 320-mile range, plenty of warning for painting terrain in the fastest aircraft. While the Landmark 8000 was initially delayed coming to market, much of the delay was a result of initial FAA certification. L-3 has flown the Landmark on every published approach in the country, both in the simulator and in real world ops with the company King Air. This is not short work. As a result, the FAA is so convinced of the integrity and reliability of the Landmark. that certification of the 8100 system is nearly complete shortly after its introduction to the FAA, partly based on the companys proven track record with the earlier certified Landmark 8000. Cessna uses the Landmark system in the CJ1, CJ2, and CJ3 light jets overlaid on the Collins Pro Line 21 suite.

The same people that brought to market the successful SN3308 Electronic HSI have introduced the self-contained, full color, multi-screen ST3400 TAWS/RMI, a Class A and B TAWS-compliant system. With its standard 3-inch ATI size, the ST3400 is designed to fit into an existing instrument cutout without the need for modifying the instrument panel, while replacing most existing RMIs.

Sandel has what it calls runway awareness which means the system recognizes every runway and tracks the aircrafts approach to it, even if there arent any published approaches for the runway.

By referencing the units internal database, the ST3400 paints the safest approach path to a given runway based on surrounding terrain. Other Sandel exclusive features include predictive altitude and virtual approach path call out based on the aircraft flight path angle instead of the actual current altitude – giving the pilots warning of what terrain they are descending into.

Like the SN3308 EHSI, the ST3400 uses the Sandel rear screen projector display technology. The Sandel spin on terrain gear is that it should be mounted we’ll within the pilots view and sharing terrain data with that of a radar display, for example, is less desirable. One of the shortcomings of the original EHSI product is that its viewing angle is limited. But from what we have seen of the ST3400 TAWS, this is no longer the case. For ease of panel installation and overall display readability, we give the ST3400 high marks.

Clearly, the market is far from saturated with TAWS-legal equipment and we cant say that one system is a better choice over the other. The existing avionics in your turboprop or light jet could mandate which system you choose and you’ll have to decide by March 29th, to meet the mandate.

We like the straightforward install associated with the Sandel unit and the KGP560 has already proven itself to be a worthy and good performing, if not suitable for every airplane out there.

If you have an MX20 or i-link MFD, we recommend the Landmark system. And, if your airplane doesnt require legal TAWS but terrain awareness is in your future, we still think that the MX20 is the best value in MFDs, with capable, seamless and intuitive terrain mapping.

Also With This Article
“Force-Fed TAWS: Blame the Deceased”
“TAWs Product Comparison”