Especially if we include Experimental aircraft, there are many different makes and models from which owners and operation may choose, each of them having their own set of features. Whether we want an aircraft to perform aerobatics, do aerial application, conduct training or even engage in cargo operations, theres a model out there, somewhere, optimized for the mission. But all aircraft embody compromises: none literally can do everything.
For example, we can trade fuel for payload, but rarely can we have plenty of both. Likewise, airplanes optimized for short-field operations usually suffer reduced cruise airspeeds and/or restricted useful load when compared to others. And primary trainers can be good at a lot of things, but regular transportation in the IFR system isnt one of them. What does make for a good IFR airplane? What characteristics should it have, and which can be omitted?
Definitions
First, we have to decide what we mean by IFR airplane. For our purposes, well confine ourselves to single-pilot airplanes with electric systems and electrical-, vacuum- or pressure-driven gyros powered by an engine. Thats a broad range, but it automatically excludes thousands of airplanes. We also can exclude those airplanes whose certification basis does not allow IFR flight.
From there, the next hurdle is a full set of flight instruments, in either a six-pack, steam-gauge configuration, all-glass or some combination. Lets presume utility is the name of the game, and we need to go places requiring communications, navigation and surveillance capabilities. That means a minimum of one comm radio, some kind of electronic navigation capability and at least a basic transponder. Even if the regulations might allow us to use radar vectors for all our IFR flying, were not going to endear ourselves to anyone by insisting on it.
Those are the basics. Of course, reliably using the IFR system requires a lot more in the way of equipment, installed or otherwise. Well get to that, but along the way there are a few more airplane characteristics to consider.
Stability
For example, the airplanes aerodynamic characteristics can be important, especially when theres no working autopilot. Hand-flying straight-and-level is boring, but relatively easy in many airplanes. I used to fly a well-rigged Skyhawk that lacked an autopilot. Since it was a Skyhawk, things rarely happened quickly, but it mostly was a hands-off airplane. When it did drop a wing, slight pressure on the opposite rudder usually corrected things. (The thing about most airplanes we fly? Theyre usually better at it than we are; were just along to choose the route and destination, and often are the source of problems, not their solution.) The sidebar above highlights the different forms of stability.
But stability in what? In each of the three axes, of course. During straight-and-level flight in calm air, a well-rigged, stable airplane will just sit there. Which is what we want. If disturbed by a gust, for example, a stable airplane will either shrug off the displacement or roll, pitch or yaw, then return to its trimmed straight-and-level conditions. Thats desirable, for obvious reasons. Even if there are no gusts, we need to have confidence in the airplanes ability to stay in the attitude we left it when we were distracted. If ATC comes at you with a revised clearance, you dont want to end up in a steep spiral after finding your pencil, writing it all down and plugging it into your GPS. Things like this are why autopilots were invented-and we consider them mandatory for any serious IFR-but you can get along without one if the airplane is stable.
And how does an airplanes stability manifest itself, anyway? Stability about the roll (longitudinal) axis is helpful when we want to maintain a heading. In the lateral (pitch) axis, its helpful to maintain altitude. Stability in the vertical axis (yaw) is important when considering flight in turbulent air, when an airplanes Dutch roll characteristics might become an issue.
Our ideal IFR platform would be similarly stable in all three axes, since different relative stability among them also can be a distracting nuisance. An example might be when the airplane is tender in pitch-perhaps due to an aft CG-but rock-steady in roll: It will hunt for its trimmed airspeed, even if it easily maintains a heading. Which highlights a final consideration for our ideal IFR platform: loading can affect its stability. With one or two people aboard, an A36 Bonanza or Piper Saratoga/Seneca might be a bit nose-heavy. Load them so the CG is near the aft limit, and they become different airplanes.
For those of us flying with decent autopilots, our airplanes relative stability usually isnt an issue. It quickly can become one, however, in the event of an autopilot or electrical failure, since most of them are electrically powered. In such an event, would you rather be flying a highly maneuverable (i.e., less-stable) Pitts Special or a less-maneuverable Cessna Caravan (a.k.a., the box the Pitts came in)?
Performance
How your chosen IFR platform performs can make it less than ideal. In this instance, were usually considering climb capability and cruise speeds. It would be easy to make some blanket statement to the effect that an ideal IFR platform should be able to maintain at least 500 fpm through 12,000 feet msl, for example, but not that many IFR flivvers need to be at 12 or higher. Most of us are quite happy at lower altitudes, where oxygen isnt necessary and even a non-turbocharged airplane can easily climb to its cruising altitude at gross weight on a hot day. That said, 500 fpm to, say, 8000 feet is something even a 172 Heavy should be able to muster. Of course, you may have special circumstances, like living in a mountainous area, where the need for a steady climb rate to a relatively high en route altitude mandates turbocharging.
But climb capability isnt the only performance metric important to instrument work. How the airplane handles runways-often in inclement weather-also is important when choosing an IFR platform.
This includes crosswind handling and braking. Obviously, the airplane needs to be comfortable on the runways available at expected destinations, including not only their length but their elevation and any obstacles that must be cleared before establishing a cruise-climb. And once you get to altitude, droning along at 150 KTAS is fine and dandy below the flight levels but a nuisance any higher. You might find yourself being vectored off an airway or an arrival to make way for faster aircraft, of which there will be many.
A final note on performance: If you plan to regularly visit an airline hub, your airplane needs to fit into the flow. Yes, ATC will try to accommodate you if 90 knots is all you can do from the FAF inbound, but everyone will be much happier if you can manage at least 120 or so to a couple miles from a long runways threshold. In something like a Skyhawk, this means using near-cruise power most of the way down the approach. If airline hubs are in your Skyhawks future, its a good idea to find an out-of-the-way airport at which you can practice keeping up your speed to the runway. Its a better idea to step up to something faster. With some retractables, this can mean flying the final at or close to the airplanes maximum gear-extended speed. Do your homework on the airplanes performance before committing to using it for IFR.
Range/Endurance
One of the reasons many of us learned to fly in the first place was to use an airplane for travel. That usually means trips of at least 250 nm-by the time you drive to the airport, pull the bird out of the hangar, etc., in most situations you almost could be there if you drove. Anything longer and the airplane is the obvious choice, even if its slow, or the headwinds make it seem so.
The old saying that the only time an aircraft has too much fuel is when its on fire is especially true when considering real-world IFR operations. Of course, the FARs impose their own range and endurance requirements but every-day IFR operations demand flexibility. That often means plenty of gas.
That Skyhawk I used to fly was a great example. In addition to the standard 20-gallon mains, it had a pair of 12-gallon auxiliary tanks mounted internally in each wingtip, giving around 60 gallons usable when everything was full. Thats a lot of time aloft at eight or nine gallons an hour, more than you may want to spend in a Skyhawk. I never felt tight on fuel when flying that airplane.
Obviously, carrying more than minimum-required fuel means we have options. In a hold, we can accept an EFC 45 minutes from now, for example, resign ourselves to stiff headwinds, make multiple missed approaches at our destination and overfly low IFR conditions on our way to something better, all without worrying too much about having enough go-juice. Conversely, not having that kind of flexibility means a higher workload as you monitor remaining options, plan shorter legs and are forced to make more fuel stops than similar airplanes with more capacity.
Equipment
Its still legal to file and fly IFR with little more than a transponder and simple VOR receiver, but serious IFR in personal airplanes demands more. Yes, a WAAS-enabled GPS with moving map should be on your shopping list, but so should some redundancy. As gadgets become more capable (see “Gadget Flight Rules 2.0“), pressing them into service when a primary system fails is only a good option if youve practiced it. A backup attitude gyro provides both dispatch reliability and peace-of-mind.
Other equipment you should consider includes thunderstorm detection-which also can be with a gadget-supplemental oxygen and a noise-canceling headset. More is better; even if you dont use all your equipment on every flight, having it and knowing how to use it effectively breeds confidence.
Close Formation
Woven throughout this article is the concept of flexibility: If you dont have enough of it, using a personal airplane for IFR may seem like too much work. Something larger, faster, better-equipped and with longer legs can make things so much easier. Once you find the right mix of airframe and equipment, and get everything tucked together in close formation, youll wonder why you ever did it differently.
Even simple airplanes can be used for light IFR-punching through a marine layer, for example, or when visibilities require filing. Theres no such thing as 100-percent reliability, and theres also no such thing as the perfect airplane for all operations. But using the wrong airplane takes all the fun out of it, and can increase risk. Choose and plan accordingly.
Jeb Burnside is this magazines editor-in-chief. Hes a 3100-hour instrument-rated ASEL/ASES/AMEL commercial pilot and aircraft owner.
