Flying Friday: the avionics brain transplant begins

I fly a 41-year-old airplane. Not that there’s anything wrong with that. As I’ve said before, there’s something to be said for mature technologies, and the economics of general aviation are such that there’s no chance I’ll be buying a new airplane any time soon when even an entry-level Cessna 172 costs north of $400K. Because new aircraft are so expensive, there’s a lively market in refitting and upgrading existing airframes. The engines, paint, interior, and avionics on an airplane can all be replaced or upgraded at pretty much any time, and the longevity of the basic airframe means that I can comfortably expect to get another 20-40 years out of my existing plane if I take good care of it.

With that said, newer airplanes have some major advantages, many of which (built-in cupholders, leather seats, ballistic recovery parachutes) aren’t available for my plane. After flying 706 for about a year, getting my instrument rating, and taking more and longer cross-country trips there were a few things that I wanted to add to make instrument flight easier and safer. My co-owner Derek and I spent a lot of time hashing out what we wanted vs what we could afford vs what we could live with. Here’s what we decided.

First off, we knew we’d have to meet Yet Another Unfunded Mandate. Starting in 2020, all airplanes that operate in controlled airspace (meaning the “Class B” and “Class C” airspace surrounding major airports and most cities) have to use a system called ADS-B. The FAA has delusions that ADS-B, which requires every aircraft to continuously transmit its GPS-derived position and velocity, will replace radar. It probably won’t, but that’s a topic for another post. Equipping a plane for ADS-B  requires two pieces:

  • a GPS system that uses the FAA’s Wide Area Augmentation System (WAAS) to provide high accuracy position and location data. The WAAS system combines satellite GPS data with position data from precisely surveyed ground stations to provide sub-meter accuracy.
  • an ADS-B Out transmitter that sends ADS-B data, including the WAAS GPS data

There are lots of ways to get these two parts, ranging in cost and complexity from “absurd” to “merely unpleasant.” The two most popular ways are to install a new transponder that includes a built-in position source or install a separate WAAS GPS and a little box that transmits ADS-B Out without touching your existing transponder. You can also get weather and traffic data using ADS-B In; that requires an ADS-B receiver and something to display the received data on. Right now, I use a Stratus receiver (the original, not the fancy 2S) and ForeFlight on an iPad for ADS-B In… but, as with many other government programs, there’s a huge catch. You get weather data for free, but you only see ADS-B In traffic if there’s an ADS-B Out-equipped airplane near you. This was supposed to be an incentive to get people to add ADS-B Out, but as a practical matter it means that ADS-B In is currently only useful for passive receivers like my Stratus in areas where there are already lots of ADS-B Out airplanes.

Next, we wanted the ability to use WAAS instrument approaches. I love the precision of ILS approaches, and use them whenever I can, but most airports don’t have an ILS, and those that do won’t typically have more than one. However, a growing number of airports have approaches that offer precision vertical and lateral guidance if you have a WAAS GPS. To be more precise (see what I did there?), we wanted to be able to fly LPV approaches so that we’d get precision vertical guidance for approaches where ILS equipment isn’t available. With WAAS equipment, you can also get an advisory glideslope, which gives you non-precision vertical guidance to help keep you from smashing into things.

Finally, we (well, mostly I) wanted to improve the autopilot’s ability to track instrument approaches. The approach phase of single-pilot IFR is a demanding and busy time, and it’s easy to make mistakes. Our existing autopilot can fly a heading, keep the wings level, and hold an altitude, but when you get to a complex approach, being able to let the autopilot turn the airplane based on GPS steering is very helpful because it frees up time and attention for vertical navigation, approach prep, and other critical tasks.

After a lot of back-and-forth, an immense amount of comparison shopping, and lots of head-scratching, Derek and I decided to send 706 to Sarasota Avionics to have the following installed:

  • An Avidyne IFD540 WAAS GPS. I preordered one of these back in 2012, well before I even had my pilot’s license, on the theory that I could always sell it later. The IFD540 is much more capable than the Garmin GNS530 and, to me, is easier to use than the Garmin GTN750. It’s also less expensive to buy, requires less expensive data subscriptions, and provides some much-needed market competition for Big G.
  • An Avidyne AXP340 transponder. The AXP340 transmits ADS-B Out, but it requires a separate WAAS GPS. In our case, that’d be the IFD540. There’s a whole complex mess of rules for which transponders can be legally used with which GPS position sources– basically, only combinations that have been certified by the manufacturer and registered with the FAA can be installed and used, even though other combinations may work just fine. Avidyne’s products are obviously certified to work with each other.
  • An Avidyne MLB100 ADS-B In receiver. Derek talked the Avidyne guys into giving us one of these for free if we bought the preceding two items. With this, the IFD540 can receive and display traffic and weather information. It is extremely useful to see this data overlaid on your primary map, especially because you can “rubber-band” your flight route to deviate around weather and traffic as needed.
  • A DAC GDC31 roll steering converter (which most people just call a GPS steering, or GPSS, adapter). Our autopilot, bless its heart, is the most analog device I think I currently own. It works by sensing voltage output from the directional gyro and course deviation indicator (CDI). To fly a particular course, you twist a knob on the DG to set the heading indicator, or bug, to the desired course; you can also have the autopilot track a VOR or even an ILS localizer, which it does by looking at the voltage used to drive the deflection on the CDI. One thing it can’t do, though, is track an actual GPS course. If the GPS route calls for you to fly a heading of 175 degrees, and the heading bug is set to 95 degrees, guess where you’re going? The GDC31 fixes that by adapting the digital steering commands output by the IFD540 into voltages that the autopilot can understand. I’ve used GPSS in other airplanes before and it’s a great experience– smooth, solid tracking with no “hunting” and accurate turn anticipation.
  • An Avidyne AMX240 audio panel. We’d been talking about replacing our ancient mono audio panel with a nicer unit that would give us better audio quality, and the marginal cost of adding the panel at the same time as the other equipment was considerably lower than doing it later.

The IFD540 + AXP340 combination gives us ADS-B Out, so we’ll be legal. The IFD540 + MLB100 gives us ADS-B In (with the added bonus that the IFD540 has wifi, so it will be able to feed all sorts of useful data to portable devices in the cockpit). Finally, the IFD540 + GDC31 gives us full two-axis autopilot coupling. I think, but haven’t verified, that it will also give us the ability for the autopilot to track altitude changes as expressed by the glideslope. The existing autopilot can track an ILS glideslope, and the IFD540 can provide a glideslope for LPV approaches (and an advisory glideslope for LNAV+V) so I think it should “just work.”

This seems like a huge list of expensive stuff (and it is)– one question that immediately comes to mind is “why bother with all this stuff when you could just use an iPad?” The problem is spelled F-A-A. First, there are no portable ADS-B solutions that are approved to meet the 2020 mandate in Part 23 aircraft. That’s a fancy way of saying that an experimental or homebuilt airplane can use equipment that’s not approved for factory-built airplanes. That also wouldn’t give us WAAS approach capability; even though there are portable WAAS receivers (including this watch!) you can’t use them to fly approaches. While there’s been lots of flailing in the aviation press about the need for cheaper, better-integrated ADS-B solutions, it’s also true that we’re getting a lot of other capability out of the upgrade that we’d miss if we went with a simpler ADS-B-only installation.

Along with the avionics themselves, of course, there are lots of little things– antennae, cables, and so on– that have to be installed and tested. That’s why we expect the upgrade to take an eye-popping four weeks– and that’s assuming everything goes well. Stay tuned!

2 Comments

Filed under aviation, General Tech Stuff

2 responses to “Flying Friday: the avionics brain transplant begins

  1. Steven

    Equipment is equipment when it comes to AVNX. Its all certified to do what it says. You don’t need to put in a whole new Honeywell or Thales or even King panel to get what you want. One point to consider, with two axis ap you are still pretty much hand flying the precision approach. You have to maintain the 393rd axis. Definatley hand flying below DH. Spend the money to set up your AP to do what it was meant to do, course/heading/alt. I am assuming the axis you will put it on will be yaw and alt? Oh and don’t forget to put money away for the resert every 2 years at a repair station. As of about 4 years ago the Feds require it for all aircraft 91/135/121.

  2. Pingback: 2016 in review: flying | Paul's Down-Home Page

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