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Decrypting the Magic Smoke - Australia's approach to new avionics technology

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It's been more than five years since the Australian ADS-B rules were finalised, but general aviation aircraft owners still face a bewildering array of products, configurations, rules and standards when investing in equipment that complies with the regulations. Andrew Andersen examines the options.

Automatic Dependent Surveillance Broadcast, or ADS-B for short, continues to rank high in hangar talk all around the country. For many owners, the IFR mandatory requirements that came into effect last year at lower levels forced their hand, and much of the IFR fleet gained new navigation systems and transponders in order to comply.

Some who had a choice simply decided to operate VFR until ready to take the plunge, whilst others confine their IFR operations to private flights in Class D and G airspace and take advantage of the temporary time extension CASA provided last year.

Whichever way you look at it, ADS-B is not going away and amazing new navigation systems, which have emerged in the last five years, complicate choices for aircraft owners.

be pretty simple: a clever device in the aircraft takes the GPS position from the navigation system and continually broadcasts it. Unfortunately, aviation engineering standards demand prescribed levels of integrity, not just accuracy.

Put another way, ATC systems need to know where, the aircraft is, and the level of confidence that may be placed in that information. Many pilots don't appreciate that the integrity requirements for ADS-B are a greater technical challenge than accuracy.

The requirements (Australia)

The legal basis for the ADS-B and IFR navigation requirements reside in CAO 20.18. That order covers a lot of operational rules, but the ones relevant here are those in relation to IFR navigation equipment, transponders and ADS-B.

IFR navigation

Performance Based Navigation (PBN) has been planned for Australia for about the same time as ADS-B, and sometimes the two subjects are incorrectly confused. P BN rules apply to only IFR aircraft.

General aviation IFR aircraft must be equipped with at least one Global Navigation Satellite System (GNSS) for flight in Australia.

There are two permissible standards:

  • TSO Cl29a equipment, which has been around for more than twenty years, and includes the familiar Honeywell Bendix King K LN 90B and K LN 94; and the "non-W" Garmin GNS 430 and 530. IFR aircraft with TSO Cl29a equipment must also have a serviceable VOR or ADF.

  • TSO C146 equipment, which has been available since 2005, and includes the Garmin GNS 430W, 530W, G1000 and GTN series of navigators, as well as the Bendix King KSN 770 and Avidyne IFD 440 and 540 navigation systems.

Even though the navigation and ADS-B requirements are separate in law, there's a big "gotcha": none of the general aviation TSO Cl29 a equipment can be used as a position source for ADS-B.

Owners of existing TSO Cl29 a equipment have to decide whether to keep their navigator and add another source of position information or replace it with one able to serve both functions.

Transponders

The rules in CAO 20.18 also include "forward-fit" requirements for Mode S transponders that apply to many VFR aircraft, too.

This doesn't mean that those aircraft have to equip with ADS-B, or even replace any equipment, but new and replacement transponders must utilise Mode S and be able to transmit ADS-B if integrated with a GNS S position source.

New aircraft, (including recreational aircraft registered with RAAus) are required to have a Mode S, ADS-B capable transponder if they operate in Class A, B, C or E airspace or above 10,000 feet in Class G airspace.

ADS-B

The regulations in Australia, the USA and elsewhere, only specify requirements for ADS-B OUT, which are broadcasts sent from aircraft.

Although there are obvious benefits, there are no regulatory requirements for ADS-BIN, where an aircraft receives ADS-B from other aircraft.

ADS-B information sent from IFR aircraft must include integrity information that satisfies the requirements of CAO 20.18 (FAR 91.227 in the USA is even more stringent).

The integrity information can only be provided by a TSO C145 sensor, or TSO C146 GNSS.

This is a big deal, because TSO C146 navigation systems are much more expensive than ADS-B transponders.

Australia permits the use of 1090ES technology only, which operates on the same frequencies as radar.

In the USA, UAT is available as an alternative for aircraft that fly below the flight levels, but it can't be used internationally and still requires a transponder.

First Fundamental: architecture

It seems many owners don't think enough about what they really need, and just ask their avionics supplier to quote "something that will give them ADS-B".

That's a bit like going into a car dealer and telling a salesperson that you want a car.

It's a fair bet that the first one you're shown won't be the smallest vehicle in the showroom. It's easy to assemble a wish-list of avionics that might be rationalised as "needed" for PBN and ADS-B.

But are they really?

We've seen above that IFR flight is perfectly legal with a 20-year old TSO C129a navigator, so what are the options to economically equip with IFR-compliant ADS-B?

1. If ADS-B is the only goal, an owner can purchase a transponder that has its own inbuilt GNSS position source, which does not need to be connected to the aircraft's GNSS navigation system.

There are three products in this category, which can be ordered with an inbuilt GNSS. Some also offer other options for traffic and weather awareness.

  • Appareo Stratus ESG

  • Garmin GTX 335 and 335R

  • L3 Lynx NGT-9000.

This approach is often the simplest, and lowest cost means of equipping with ADS-B, with deals available for supply, installation and paperwork for less than $10,000.

The downside is that these systems offer the pilot nothing more. A variation of this approach, which some aircraft owners have chosen, is to equip with a separate, stand-alone GNSS sensor, certified to TSO C145, interfaced to an ADS-B capable transponder.

This can be attractive in aircraft that already have a suitable transponder, but an older TSO C129a navigation system.

Products in this category include the Trig TN70, Aspen Avionics NexNav Mini, and the Freeflight Systems 1201 and 1203C sensors.

Professional advice is needed before purchase, since not all sensors can be readily integrated with all transponders and costs vary between manufacturers and models.

On their own, these products don't provide large-format displays, additional navigation information, or replace round-dial instruments.

All they do is provide GPS position information, with the required integrity parameters, to a compatible transponder; but it will give an aircraft perfectly compliant ADS-B, often at less than a third of the cost of other alternatives.

2. Owners who want new navigation systems can purchase new GNSS equipment certified to TSO C146.

When connected to a new ADS-B compatible transponder, the aircraft will satisfy the ADS-B requirements, and often please the pilot with a satellite navigation system that extends far beyond the basic capabilities of GPS 20+ years ago.

This approach can be expensive, however: installing a larger format new GNSS products, such as the Garmin GTN 750, Bendix King KSN 770, or Avidyne IFD 540 will cost upwards of $25,000 and that is before the cost of a new ADS-B transponder.

There are deals to be found, especially if pre-owned equipment is acceptable or existing equipment can be traded.

Consider compatibility between the navigation system and transponder, not just now, but in the future.

Choosing the same manufacturer for both reduces the risk of future incompatibilities when upgrading to new software revisions.

There is plenty of choice in the navigation systems market, as discussed below, and owners often choose to enhance new navigation systems with additional, or replacement, compatible equipment, including:

Primary Flight Displays (PFD), such as the Garmin G500/600 ft series and Aspen Avionics display families.

PFDs can replace the round-dial attitude indicator, altimeter, and airspeed indicator, although aircraft certification rules often require retaining some of the old instruments for backup.

The most recent PFDs have sharp, full colour displays, and include electronic attitude and heading reference (AHARS ) systems, and optional synthetic vision and a range of available interfaces to other equipment.

They are not cheap but provide the pilot far greater situational awareness than older analog instrumentation.

Multifunction Flight Displays (MFD) are used to present navigational, weather and traffic information to the pilot.

Whilst an MFD is incorporated in the large-format new GNSS products, it is not unusual to find aircraft fitted with an addition MFD to display ancillary information, such as charts, weather or traffic.

Princely Sums

Prices for PFD and MFD installations vary enormously depending on the complexity of the installation and interfaced equipment and except for the most simple, VFR-only installations, run to another 5-figures.

As a very rough guide, retrofitting an IFR piston single with new GNSS, ADS-B transponder, and PFD/MFD can cost $70,000 or more once design, installation and engineering approval are considered.

PFDs and MFDs do not include GNSS or transponder functions. Typical PFD installations include pitot-static plumbing, altitude encoder connection, and interfaces to GNSS, autopilot, ILS/VOR, ADF, temperature, weather and traffic sensors.

Choosing a Navigation System

From here, let's assume that you've decided to have a new navigation system installed in the aircraft.

There are a couple of important things to know at this point:

New GNSS systems are computers, not instruments.

Not only is there a lot to learn in buying and installing one, but there will also be a lot to learn in using it properly. Like all computers, GNSS systems have:

- Hardware, with multiple electrical connections, much associated wiring and components that need cooling and careful handling

- Software, that will change between revisions provided by the manufacturer, and which you will probably upgrade several times during the life of the product to obtain new functional features and improvements.

- Data, which comes from:

  • Sensors on the aircraft - for example, altitude encoder, GPS antenna, weather and traffic sensors, where fitted.

  • Input from the pilot - for example, flight plans, user waypoints and direct-to commands.

  • External sources - particularly as navigation, chart and terrain/obstacle databases.

GNSS systems communicate with other avionics in the aircraft using one or more standard communications protocols or formats, which are usually exchanged over an ARINC 429, Ethernet, or RS-232 serial interface port. If this all sounds like gobbledygook, relax ... you're far from alone.

Matching protocols and ports is a task for an avionics professional, but mentioned here because not all functional capabilities are available for all protocols and interface ports.

For example, curved procedure legs may not be displayed on a PFD when connected to a GNSS with RS-232, but some revisions of transponders must use RS- 232 connections to generate compliant ADS-B output.

The need for detailed product knowledge and installation skills are why purchasing from an accredited avionics supplier able to provide installation services and after-sales support is so important.

GNSS systems do the same things differently, and whether one is preferred over another is often a subjective assessment.

Whilst all GNSS systems do the same basic stuff, there are big differences in the way different products work.

Those who learned to fly in the 70s or 80s remember when nav/ comm radios all had similar, basic controls, and a King Silver Crown VOR worked exactly the same as Collins or Narco; a pilot would get out of one aeroplane and into another without giving the nav receiver a second thought.

This is not true now, and it's not just the GNSS functions, because most GNSS systems are actually complex Flight Management Systems (FMS), and often replace the humble nav/comm radio.

It's advisable to study the pilot's guides, and get a demonstration before committing to purchase anything.

— Size and Form Factor:... older GA aircraft frequently have limited panel space, so often the first decision about a new navigation system is its physical size.

If you have the room, the 175-mm diagonal Garmin GTN 750 display is the most impressive of the retrofits, but if a separate PFD/MFD will also be available, it might not be worth around 90 mm of panel height.

However, the map features on smaller-format products are necessarily limited, and they can't display Jeppesen charts, as the larger-format models can.

- User Interface:

Style and type of menus?

The Garmin GTN series is big on touch-screen icons, which take the user through nested menus without surrounding hardware buttons.

The Avidyne menu selections can be made with either hardware buttons or touch-screen, and use little nesting, so you can move fast between functions.

Bendix King menus are consistent with those of Aspen Avionics, including user-definable split screens, which may be appealing in aircraft already equipped with an Aspen Avionics PFD.

Touch screen, soft or hard keys (buttons), or both?

Touch screens have the advantage of maximum flexibility and presentation size: the unit can switch from an alphanumeric keyboard to a digital key pad without any input from the user, and if there are no buttons, the screen can be larger, and easier to read. On the other hand, some pilots find touch screens harder to use in turbulent conditions.

The Garmin GTN series are all touch screen, with dial controls for volume and emergency use, whilst Avidyne and Bendix King have both touch-screen and hardware keys around the display edges; the KSN770 also has a cursor control device, similar to large aircraft avionics.

  • Alerting and status displays vary between products and may include external annunciators

  • Display customisation, allowing pilot choice of where and how navigational and other information is shown.

Screen Resolution: The clarity of text and graphics is a function of display colours, brightness, and resolution.

In the large-format products, the Bendix King KSN 770/765 and Avidynes IFD 550/540/545/510 models are 640 x 480 pixels, while Garmin's GTN 750/725 models are 600 x 708 pixels.

The smaller format products from Garmin are 600 x 266 pixels, whilst those of Avidyne are 640 x 235.

Don't get obsessed with these figures, though: lots of pilots are into their second decade of flying with the Garmin GNS 430, which has a display resolution of 240 x 128.

Screen resolution varies among PFD and MFD products, with Garmin's G500/600 TXi now the clear leader in that space at 480 x 800 pixels for the portrait format display.

More powerful screen resolutions show off 3D synthetic vision functions, and detail such as charts and airways/waypoint labels, far better than earlier, lower resolution models.

Features, Features, Features: All these systems do almost all these functions, one way or another. The real difference between them is how the functions work:

Graphical navigation map: more detail, on the larger products, is more useful. Look out for:

- Ease of zooming (in and out) and panning (moving around) the map.

-Cluttered screens, and clarity at different zoom levels.

- Colours, including the ability to dim or remove at night.

-Geo-referenced Jeppesen charts (Airservices Australia charts aren't available), and how they are displayed. This also means being able to easily change the map orientation from heading or track-up, to north-up.

- Graphical (drag and select) flight planning and modification on the map screen.

- Integrated attitude reference and synthetic vision, which is only available in the Avidyne IFD 550, which for some aircraft owners, might mitigate the desire for a separate PFD.

• Flight plan entry, either by the use of waypoints or routes.

• Terminal procedure selection, including finding the best initial approach fix, activating the procedure, and suspending it, for example, when holding.

• Support for wireless interface to upload a flight plan from, or interact with an EFB tablet, and to load navigation database updates from a computer.

• Waypoint/name completion: Avidyne calls this feature GeoFill, whilst Garmin's corresponding feature is FastFind.

• Integrated Nav/Comm radio, including options for higher (16W) transmit power.

• Vertical navigation, including time to top of descent, required rate of descent, altitude labelling of approach legs, and related functions.

• Integration capabilities, especially to display radar and Stormscope weather, traffic, audio panel, transponder functions, PFD/MFD, fuel flow and autopilot compatibility.

• SBAS (WAAS in USA): all TSO C146 systems have SBAS capability, but it will only be any use if the current trial produces an operational, ICAO-standard SBAS for Australia.

• Other features including check lists, nearest airport/navaid/ waypoint information, holding patterns and sector entries, terrain and chart databases.

• Database updates, including cost, source and availability of updates. Garmin and Avidyne databases for Australia are currently sourced only through Jeppesen, and Australia-only databases are only available for Garmin. Bendix King database updates are obtained from Honeywell.

Garmin products use a specially-encrypted data card, whilst Bendix King and Avidyne systems utilise a USB stick.