Understanding and equipping for different GPS-based approaches

What you need in the cockpit along with training to take advantage of the latest precision space-based landing systems.

CMC's CMA5024/5025 LPV upgrade kit.

According to Garmin Intl Avionics Product Mgr Bill Stone, there are tens of thousands of GNS400 and 500 series navigators in the field. The previous-generation non-WAAS units are capable of flying LNAV procedures only.

However, as nearly half of their owners have found out, the upgrade is easy. Your local Garmin dealer can replace the antenna and send the unit in for the upgrade to WAAS. Garmin has STCs for approximately 900 different aircraft.

Furthermore, the new units have a feature to make vertical guidance available on most LNAV procedures by selecting the "LNAV+V" option. This allows for a stabilized descent to the MDA, avoiding the less desirable "dive-n-drive" style approach of the last century.
You are not grounded if your current avionics supplier does not have an upgrade solution that suits.

According to Esterline CMC Electronics Mgr New Business/ Alliances Dave Bailey, his company's IntegriFlight CMA5024 provides a unique solution. It is a black box GPS, certified to both TSO-C145 and C146.

When paired with the small CMA5025 control panel (see figure above), it provides an LNAV, LNAV/VNAV and LPV solution that is compatible with most ILS/DME receivers and calculates the required ILS lookalike signals to drive the displays and the autopilot.

The CMA5024 is wired in between the existing ILS and DME receivers and the rest of the aircraft systems. In ILS mode, these signals are passed straight through the CMA5024 and then to the rest of the aircraft as before.

In GPS landing system (GLS) mode, the CMA5024 calculates the ILS deviations and DME distances and feeds these to the indicators and autopilot instead. The CMA5025 is used to select the appropriate WAAS channel for the desired procedure. The solution is totally independent of the FMS, if installed.

To upgrade or not to upgrade

That is the question if your favorite airports don't have LPV procedures or if you operate outside WAAS coverage. If your airport doesn't have an LPV procedure, it soon will. Look at it from an airport operator's point of view—it costs several million dollars to install and calibrate an ILS, versus a few tens of thousands to design and publish an LPV procedure.

Further, FAA's WAAS concept is being duplicated around the globe. Japan's multifunctional satellite-based augmentation system (MSAS) and the European Geostationary Navigation Overlay Service (EGNOS) are operational and India's GPS-aided geo augmented navigation (GAGAN) should be approved for aviation use this year.

Even if you are outside the official coverage area for LPV procedures, you can still take advantage of the satellite integrity information so that you don't have to worry about RAIM calculations. Regulatory agencies are starting to publish WAAS (or equivalent) Notams to advise of nonavailabilities.

ADS-B is another system that depends on the improvements that come with a TSO-C145-compliant GPS. The accuracy necessary to comply with the requirements of both ADS-B In and ADS-B Out can most easily be provided with WAAS GPS.

The bottom line is that, for all these reasons, you should be upgrading your equipment as soon as practical so that you can take advantage of the precision GPS approaches and the higher level of GPS service.

Mike Venables is an aviation consultant and freelance writer. The principal at TriLink Technologies Group, Venables has been involved in the aerospace industry for more than 40 years, including aero engine, airframe, avionics and simulator manufacturers.


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