Used Light Twins Roundup

General aviation manufacturers once offered nearly as many choices of twin-engine airplanes in their product line as singles. For the 1980 model year, Cessna built no less than 11 twin-engine piston models, Piper had eight twins in its lineup, and Beech sold seven different non-turbine twins. It was the heyday of personal flying; fuel was relatively cheap, new airplanes were affordable, and a lot of pilots were looking to upgrade.

But, following the overall malaise of the economy in the late 1970s, a general aviation decline was coming, and irrational exuberance quickly gave way to realistic parsimony. Twin-engine planes became ostentatious appurtenances, steadily waning in popularity during the last two decades of the century. Today, with demand for multi-engine planes at a low ebb, there are real bargains to be had in a 50-something-year-old twin, at least from an acquisition standpoint. A figure between $100,000 and $200,000 will buy a twin that once would have fetched twice that amount.

What was the original purpose of the light twin? And is there still a place for these capable machines, once sought-after business tools/family cruisers? And what brought about their fall from favor? Those are all big questions that we'll try to answer. 

As a generalization, "light twins" are more or less defined by their 6,000-pound maximum takeoff weight. Different certification standards apply if the airplane weighs more than 6,000 pounds or has a landing-configuration stall speed in excess of 61 knots. In that case, it must produce a single-engine climb rate at 5,000 feet MSL equivalent to its Vso squared times .027 (not much) and, for post-1991 certifications, a climb gradient of 1.5%. If the twin-engine airplane weighs no more than 6,000 pounds or stalls at less than 61 kts (70 mph), the FAA does not require ANY capability of sustained level flight at 5,000 feet with one of the two engines failed---merely that engine-out performance be determined, good or bad. This is, needless to say, a much lower certification bar for manufacturers to shimmy under, so 6,000 pounds is a bit of a magical figure.

In addition, the airplane must be controllable with the "most critical" engine windmilling at Vmc(a). Except for very early twins, this Vmc speed is marked with a red radial on the airspeed indicator, and a similar blue radial is depicted to show Vyse, the speed that produces the best single-engine rate-of-climb, or at least the minimum descent rate, depending on conditions.

During the 1970s, it became fashionable to furnish turbocharged engines on twins, not so much to enable high-altitude flight as to enhance their single-engine rate of climb and service ceiling.

All of these foregoing distinctions aside, for discussion purposes, we often simply consider a light twin to be a multi-engine plane used for personal and business travel, one probably intended to be flown by its owner rather than crewed.

While the manufacturers' marketing departments and design engineers will have determined, sometimes through creative flight testing, a positive single-engine rate of climb and generous engine-out service ceiling, in order to show some favorable brochure figures, the experienced factory test pilot will have had a new well-running airplane to generate these numbers; be assured that your actual mileage may vary.

So long as both engines are healthy, light twins fly with élan and feed a pilot's ego quite nicely. Control forces may be somewhat heavy and response a bit ponderous, but the heavier wing loading and necessarily larger tail feathers make for a stable, comfortable ride. Most of the upgrading pilot's transition training will focus on handling the airplane with one engine failed, learning how to maintain control, and maximizing any remaining performance.

For the majority of the light twin models, I have always divided them into one of two categories: those designed from the outset to be twin-engine airplanes and those developed from single-engine predecessors. It follows that those in the first classification will have somewhat better cockpit layouts and (if properly designed) more big-plane handling. Those "twinned" from singles will have familiar interiors for the transitioning pilot who is moving up in sibling order and may fly somewhat like a mature version of the single-engine foundation airplane.

Examples of purpose-built twins are the Aero Commanders, Beech's Twin Bonanza and Duke, the twin Cessnas, Piper's Apache, Aztec and Navajo airplanes, and the Smith Aerostars. Twins grown from singles would include Beech's Duchess, Travel Air and Baron, and Piper's Twin Comanche, Seneca and Seminole. Somewhat in between are the unique Cessna Skymaster and the Grumman Cougar, both of which bore some single-forerunner relationship but became more twin-like in execution.

At the risk of over-generalizing, I've found that ab-initio twins are more content to accelerate well-past Vmc(a) with all three feet on the ground during takeoff, requiring a purposeful rotation into an intentional liftoff and will land equally predictably if loaded properly. Most of the second-generation light twins, those grown from a single, prefer to fly themselves off at or near minimum-control speed and may tend to wheelbarrow onto the nosewheel during liftoff and touchdown, particularly if loaded to the forward CG limit. In all cases, you have to understand the particular demands of each airplane type and fly it accordingly.

The most prima facie obvious justification for having two engines is to negate the single's inherent hazard of failure in its one and only powerplant. The theory being, the twin will be able to successfully continue flight on a single engine so that it can wind up on an airport instead of in a field. When flying at night, in low IMC, or over water and inhospitable terrain, the twin-engine airplane bestows a measure of confidence onto its occupants.

The dirty little secret of light twins is that as airplanes scale up in payload, speed and range capability, the real purpose of a second engine is simply to make the plane fly. It takes all of the combined horsepower to haul the extra people and fuel in the desired manner. The perceived safety enhancement of redundant powerplants is secondary from a design standpoint because the vast majority of the airplane's life is spent with both engines running.

Consider a twin-engine airplane with 200-hp engines that requires a minimum of 150 hp to maintain level flight. With both engines at full power, there's 250 extra horsepower available to create an exhilarating climb and cruise speed. When one engine fails, only 50 extra horsepower is available, resulting in an anemic climb rate and a much-depressed service ceiling.

And so, demonstrating the light twin-engine airplane to a prospective buyer moving up from a high-performance single always focused on the acceleration during takeoff, rapid climb rate and high-speed cruise, with a glance directed at the big cabin following behind. That enchantment with miniature-airliner capability is what sold twin-engine airplanes. The engine-out performance may have been given but passing reference, perhaps with a quick demonstration of a zero-thrust maintenance of level flight, always with a light load to enhance its success.

The other attractions of twin-engine airplanes over singles are their redundant sources of electrical power, deicing and pressurization, greater seating and baggage capacity, a bigger instrument panel and less engine vibration transmitted to the cabin. The two-motor airplane's wing and power loadings make it a great instrument-flying platform.

When it comes to getting the most bang for the buck in terms of operational and ownership costs, the logic meter swings toward a high-performance single-engine airplane, so long as you're only carrying a couple or a small family. The realities of living during the recessionary economic cycles we saw in the latter decades of the 20th century left personal twins fading fast in popularity. It wasn't just the cost of the increased fuel burn. The fact is, putting a twin in the hangar doesn't double the ownership cost of a single; it easily triples it or more. One might even start with needing a bigger hangar because twins tend to be wider and taller. And then there's the matter of insurance cost or even its availability.

On top of that, twin-engine safety, as it turned out, has proven to be somewhat elusive. Although successful returns to an airport with an engine feathered often go unreported, when a less-than-skilled pilot loses control of a single-engine twin, the accident tends to be horrific in outcome. So, the fatal accident rate after an engine failure is much worse in twins than in singles. Not only does the twin with wing-mounted engines require precise and correct flying when one engine quits, but any resultant crash will occur with exponentially more kinetic energy. Single-engine planes are, by and large, limited to 61 knots maximum stall speed in landing configuration; twins have no such certification requirement and may arrive at 90 knots even if flown into the ground under control. If you're looking to survive an accident, plan to do it in a single.  

Insurance underwriters are only interested in exposure to risk of loss and the cost of meeting outlays to cover claims. More seats, more expensive accidents, more chance of a pilot's skill not being up to the challenge of flying the twin---all of these mean insurance can be a problem. To be insurable, the aspiring multi-engine pilot will probably have to go through initial and recurrent type-specific training, even though they have satisfied the FAA by adding a multi-engine rating to their license. 

As much as anything, the decline in light-twin popularity may have stemmed from the "corporatization" of general aviation manufacturing. Airplane companies are no longer run by designers and pilots who are justly proud of the company's aviation portfolio, of which twins were a natural progression. Today's business-oriented management saw an excess of models overlapping in the product line and reduced the offerings to streamline operations. No longer does manufacturer advertising promote fast, flashy twins to jaded single-engine pilots, focusing instead on sensible singles. On paper, at least, most of the twin's work can be done with a big single.