Few general aviation aircraft are as iconic as Cessnas 310. Whether because of its aggressive ramp presence, its supporting role in an old television adventure series or its suitability for a wide range of missions, the 310 is what many non-pilots recall when piston twins come up in conversation. Its arguably the first modern light twin and certainly a classic.
While the 310 is all of those things, its also a complicated machine, production of which ended almost 30 years ago. The tall landing gear might be thought of as delicate and its systems demanding, both to maintain and operate. But it still offers substantial transportation value, and the many different variants that were built as the model evolved means it shouldnt be hard to find the right one for your mission.
Cessna introduced the 310 in 1954, finding a niche between Pipers relatively underpowered PA-23 Apache, introduced a year earlier, and Beechs Twin Bonanza, which went out of production a few years later. It competed most directly against the Aero Commander 520, but that model was discontinued the same year. The 310 was Cessnas first all-metal, modern twin-replacing the pre-war T-50/AT-17 Bamboo Bomber-and was clearly focused on business transportation. It foreshadowed the companys subsequent products and helped usher in its future growth.
And its featured presence in the 1960s television drama, Sky King, didnt hurt anything. Its namesake hero, played by Kirby Grant, upgraded to a 310B shortly after that model became available. Named Songbird, the airplane (several were actually used during the shows production) was as much a star of the series as its actors, perhaps becoming the main reason for the shows popularity on Saturday mornings throughout the 1960s, and even today on DVD.
Cessnas aggressive pursuit of the business market manifested itself in not only the 310s looks, but also its refinement: Many production years saw a new model designation. Cessna brought out the 310B in 1958, the 310C in 1959 and the 310D in 1960, eventually getting to the 310R in 1975 (with a few gaps) before ending production in 1981.
The first 310s came with 240-HP Continental O-470-B engines. From the beginning, a sleek, powerful appearance was a design goal, with tight cowlings and streamlining at the nose and tip tanks (at least by the standards of the day). Split wing flaps eliminating the need for external brackets or tracks and their drag. Distinguishing features of the early models are multiple aft side windows, a straight tail and noncanted tuna tanks, named for their shape.
When the 310B came out in 1958, it brought with it a 100-pound boost in gross weight. For the next years 310C, an engine change and gross weight bump occurred with the fuel-injected, 260-HP Continental IO-470D. The TBO was 1500 hours, same as with the earlier powerplants. For the 1960 310D, Cessna swept the tail, as it was doing across its fleet.
The next significant change was in 1962, with the 310G. Cessna introduced canted Stabila-Tip tanks, said to be more aerodynamically efficient than the old design. The original noncanted and bladder-equipped tip tanks also had a fuel-pickup problem; an airworthiness directive mandated a hefty increase in unusable fuel. With bladderless all-metal canted tanks, swept fin and short nose, its arguably one of the most attractive light twins ever built.
Cessna didnt stop there. Cabin size was increased, along with gross weight. What started as a five-place twin became a six-placer with 1963s 310H. By next years 310I, wing lockers and auxiliary tanks became options, as did three-blade props. One significant difference was the switch from the corrosion-prone overwing exhaust design to an improved underwing arrangement on the 310I. An engine change accompanied the modifications, to the IO-470-U, still of 260 HP and still with a 1500-hour TBO. Another engine change, to the IO-470-V, occurred in 1966 (310K), along with extended, one-piece aft windows on each fuselage side.
In 1969, Cessna consolidated its model line, offering a turbocharged variant of the 310 alongside the normally aspirated 310P and dropping the 320. The T310P came with 285-HP Continental TSIO-520-B engines (1400-hour TBO), three-blade props and a 5400-pound gross weight, compared to the normally aspirated 310Ps 260-HP IO-470V Continentals, optional three-blade props and 5200-pound gross.
From 1970-1974, Cessna stuck with the 310Q and T310Q, despite bumping gross weight on the 1972 T310Q to 5500 pounds (5300 for the nonturbo version) and changing to wraparound Omnivision windows by adding a pair of small panes at the top of the aft cabin.
In1975, the 310R II and T310R II sported one of the biggest changes since the types tail was swept: an extended nose. The probiscis grew 32 inches, housing a sizable baggage compartment. The normally aspirated version also got 285-HP Continental IO-520-M engines (1700-hour TBO) and another 200 pounds were added to the gross weight-bringing it to 5500 for both the turbo and nonturbo versions-along with improved landing gear.
The 310R marked the airplanes final configuration, which continued until the line was closed down in 1981. Some 5700 copies of the 310 were manufactured, not including its various military versions. The 310Rs are the most numerous, followed closely by the 310Q, a result of sticking with one model for several years.
An old saying about piston twins-they have two engines because they need two engines-refers to whats necessary to obtain their performance and their handling when one engine fails. Both are strong points of the 310, especially the turbocharged versions. Early models feature high-speed cruise in the neighborhood of 175 knots while later ones will top out at around 190. The turbo models can present 225 knots at all-out max cruise, but the fuel burn will be breathtaking. Reduced power settings get 175 knots on later, non-turbocharged models.
Engine-out performance is better than average, with normally aspirated 310s achieving a single-engine service ceiling of just under 7000 feet to 7500 feet, depending on model. Turbos see SE service ceilings of 17,000-18,000 feet climb rates from around 330 to 440 FPM, depending on model and turbocharging.
Figure cruise fuel between 20 GPH for an early, nonturbocharged 310 at economy settings up to 35 or more when flogging a big-bore turbo. Join the Church of the Lean-of-Peak and shave that down to around 28 GPH. Airspeed suffers, of course. Double those numbers, at least at the low end, for takeoff and initial climb.
Speaking of climb, the non-turbocharged models do OK in the low teens and turbo models in the high teens, although their service ceilings can be as high as 28,200 feet (T310Q). Theyre happiest in the mid to high teens: One owner told us, At FL250 [the T310R] performs like a very expensive Skylane.
Book short-field performance is surprisingly good, especially for the airplanes weight: Landing over a 50-foot obstacle in a 310R will consume 1790 feet, compared to a Model 58 Barons 2498. Taking off over that same obstacle will require 1700 feet in the 310, while a Baron needs 2100 feet. Perhaps unsurprisingly, pilots and owners treat the book numbers with a grain of salt, reporting poorer real-world numbers.
Once airborne, however, 310s provide an extremely stable platform. The only fly in the ointment is the types tendency to Dutch roll, especially in turbulence and in an inexperienced pilots hands, caused in part by the high rotational inertia of fuel in the tip tanks. Experienced owners tell us Dutch rolls are easily damped with proper technique.
As clean and powerful as the 310 appears, it can get draggy on approach. Relatively large props blank out much of the wing and split flaps produce much more drag than lift. This can be a good thing, since the clean airframe can be difficult to slow down until the first notch of flaps is deployed.
Early models came with an approach-flap extension speed of 140 knots, with full deployment available at 120. The 310K bumped the approach-flap speed to 155 knots or so. Subsequent models through early 310Rs are placarded for 160 knots approach-flap extension and 140 knots for full flaps. Drop two knots from those numbers for late 310Rs.
Loading, fuel system
For the early models, up through the 310G, interior space is about average for baggage, which means having to stow some items under and between seats, or at passengers knees. Beginning with the stretched cabin of the 1963 310H, more baggage space was opened up. Wing lockers, whether installed at the factory beginning with the 310I or in the field, can help, as does the 310Rs nose baggage compartment. Removing the aft row from the six-seat airplanes-quick-disconnect seats were optional on later models-can help, too.
Weight and balance must be watched closely. The first nose extension-a small one-occurred with the 310K. But by the 310I, cubic feet available began to exceed the airplanes weight-lifting capability. No longer could a pilot cube-out a 310 before overgrossing it and it could be loaded out of forward c.g. Adding lots of avionics and other options to the typical model only compounds the problem by upping the empty weight. One solution is STCd vortex generators that can boost max gross by 100 pounds or more. That said, you can find late-model 310s with close to 2000 pounds of useful load.
The 310s full-fuel payload varies depending upon the model, equipment and fuel tank arrangement. Total usable fuel capacity can be 100, 132, 142, 183 or 203 gallons-from 600 to 1218 pounds of fuel. Full-fuel payload in a lightly equipped 310C with auxiliary tanks might exceed 700 pounds, while it could be as low as 400 pounds in a 310R. Other loading and operating considerations, like maximum landing weight and zero fuel weight, were introduced with later models.
While were talking about payload is a good time to point out the 310s fuel system on airplanes with all the optional tanks is more complicated than others. It also has a number of idiosyncrasies.
The complications start with nomenclature. Ask a line person where the main tanks are on a given airplane, and theyll likely point to the wing. With the 310, theyd be wrong. Early models only came with the 50-gallon-per-side tip tanks. As there were no tanks in the wings at all, those were main tanks. As time went on, horsepower increased and so did demands for fuel. First came 20-gallon wing-mounted bladders, followed by an additional 11.5-gallon bladder, for 31.5 gallons in each wing. Then came 20-gallon tanks in the wing lockers. In a 310R, as much as 203 gallons can be available.
If the pilot has the mains topped and takes off without checking the fuel actually went into the right spot, you can guess what might come next.
Thats not the only tricky thing about the 310s fuel system. A fully equipped 310 with wing locker tanks can have up to 10 fuel drain points and eight fuel pumps. Connecting all this is a relatively complex (when compared to other piston twins) plumbing system. Theres no separate gauge for each tank, though the gauge does switch automatically to read the tank being used (but not the wing locker tanks, which have no fuel level senders). The pilot can read the tanks not in use by toggling a switch. Confused yet? Theres more.
Fuel feeds to the engines from either the mains or the aux tanks (but not from the wing locker tanks, if installed). Presuming the mains were full at takeoff, at least an hours fuel has to be burned off if the airplane has 20-gallon aux tanks (90 minutes for 30-gallon aux tanks) because excess fuel is pumped back to the mains. If there isnt room for it in the mains, it goes overboard.
The mains also are the receptacle for the contents of the wing locker tanks and there has to be room for transferred fuel. The pilot should wait until there are 180 pounds or less in the mains before pumping from the locker tanks.
The aux tanks feed directly to their respective engine, and the only pump serving them is engine-driven. In the event that pump or engine fails, the aux tank on that side could hold 30 gallons of dead weight; theres no crossfeed from the aux tanks to the opposite engine.
Hopefully youll never discover this factoid the hard way, but those big tip tanks were originally designed as a safety feature, to get fuel as far from the cabin as possible. Early on, a prototype landed gear-up and the tip tanks separated just as they were designed to do, with no post-crash fire.
The good news? The 310 is not unduly prone to fuel mismanagement accidents, so despite the systems apparent complexity, pilots seem to have little trouble dealing with it. All those tanks can carry a great deal of fuel making six- or seven-hour endurance possible in later models. Early models go for four to five.
Landing gear, maintenance.
Lots of attention on the landing gear. Its relatively tall and, as a result, often thought to be more delicate than with other airplanes. Also, all that fuel hanging out on the wingtips tends to create high side loads.
As with so many other general aviation landing-gear systems, one of the keys is finding a technician familiar with and knowledgeable about it. The 310s gear system includes a number of components requiring proper rigging during regular inspections. Done properly, trouble can be avoided, but failure to treat the gear with respect increases the odds of failure dramatically.
People with keen familiarity with the 310 tell us of three weak points in the gear system. The nosegear idler bellcrank, located under the pilots feet, is probably the worst since its failure-always at retraction, and always loudly-means two prop and two engine teardowns.
The main-gear torque tubes and inner landing-gear door actuator bellcrank are the other two. If the torquedetect and correct cracks and corrosion in the exhaust system, which could lead to an uncontrollable in-flight fire, and was the subject of extensive negotiation among operators and the FAA during the late 1990s. Since it became effective, there have been no further exhaust-related accidents in these airplanes, according to those involved with its development.
Another one is AD 90-02-13, which covers the main landing gear barrel inner bearings. It applies to the 310, 340 and all piston-powered 400 series Cessnas except those with trailing link main gear and requires inspections for cracks, including magnetic particle inspection, every 1000 hours or the replacement of the bearings with an improved part.
The props are subject to a couple of ADs: these include the infamous McCauley prop inspection AD (95-24-05) and 94-17-3, repetitive inspection of the prop hub grease fittings.
Other notable ADs include: 98-1-8, replacement of two-piece carb venturis with one-piece units; 97-26-17, ultrasonic inspection of the crankshafts with possible replacement; 96-12-22, repetitive inspections of the engine oil filter adapters; and 96-20-7, repetitive inspection of the combustion tubes on the Janitrol cabin heater.
Type clubs, market
When considering an airplane in production for almost 30 years, and with so many variants, it shouldnt come as a surprise 310 prices vary widely. An early straight 310 averages only $26,000 or so in todays market, rising to $133,000 for a turbocharged T310R, per the Aircraft Bluebook Price Digest. Between those extremes, theres no real spike. Instead, each successive model sees a modest increment in price. The gap is closing between the 310Q and 310R-the 1974 310Q averages around $87,000 while the 1975 310R goes for $93,000. The gap for the turbo models is similar.
Modifications for the various 310 models run the gamut, from the usual avionics upgrades to improved cabin heaters, auxiliary fuel tanks in the nacelles and cabin, and electrically de-iced props. Other mods include vortex generators (VGs), something we highly recommend for all twins when available. They often come with gross-weight increases, as they can reduce critical speeds. Check Micro Aerodynamics (www.microaero.com, 800-677-2370). PowerPac Spoilers (www.powerpacspoilers.com, 800-544-0169), as their name implies, offers a spoiler kit for the 310R; it requires the Micro Aerodynamics VG kit.
Engine and prop upgrades are available from Colemill Enterprises (www.colemill.com, 615-226-4256) for the 310F through R, and may come with gross-weight increases. A choice of IO-520s or IO-550s is offered; prices and performance gains depend on aircraft model and options selected. Also, RAM Aircraft (www.ramaircraft.com, 254-752-8381) offers engine upgrades for the 310R, but mainly focuses on upgrading powerplants for the turbocharged 310 models.
One of the popular mods, at least for early 310s, was developed by Riley Aircraft Corp., which re-engined 470-powered 310s with a pair of Lycoming IO-540s. The Riley Rocket conversion used normally aspirated engines, with the Riley Turbostream adding a pair of Rajay blowers with manual wastegates. The conversions turned early 310s into rocket ships, but the company has long since gone out of business. Keep that in mind if considering a Riley 310.
All piston-powered twin Cessnas have their own support organization in the form of The Twin Cessna Flyer (www.twincessna.org, 704-910-1790), headed by Bob Thomason. Originally named 310 Owners of America, membership gets you a newsletter and the right to attend worthwhile seminars on operations and maintenance. Overall, however, the Cessna type club of choice would be the Cessna Pilots Association (www.cessna.org, 805-922-2580), which serves all piston-powered Cessna owners with a monthly magazine and detailed, model-specific support.
Ive operated a 1967 310N with a Colemill Executive 600 conversion (300 HP IO-520-E engines) for the past four years and 700 hours. My primary use of it is rather unusual as I am the president of Cloud Nine Rescue Flights (www.cloudninerescueflights.org.) Our normal mission is loading the plane with dog cages and flying on trips of over 1400 nautical miles, which we are able to do in under eight hours with a fuel stop.
I find it to be a fabulous plane that is undervalued in the marketplace. Despite acquiring the plane with engines at TBO and having some avionics failures that required costly upgrades, total all-in cost has been approximately $350 per hour. This includes overhauling both engines and accomplishing a number of other maintenance items at the same time. If I prorate the overhaul cost, it ends up being closer to $300 per hour. All this for a plane with two engines, six seats, a comfortable cabin and noncertified anti-icing. Plus, at 6000 feet it can fly at 190-195 knots true airspeed on 27 GPH combined, or 177 knots on 23 GPH, lean of peak.
While I operate my 310 out of a 2800-foot runway, I feel the 310 is best suited to runways of 4000 feet or longer for a comfortable margin. Still, I have taken the plane into runways as short as 1900 feet.
Although a 310 is a six-seater, it is best used for four or fewer adults. The rear two seats are best served for small people, ideally children. As a four-person plane, it provides generous baggage space, especially with the wing lockers. The 140-gallon standard fuel on the earlier models provides over five hours endurance. This is more than sufficient for most flights. A 310R with all the possible extra fuel can have over 200 gallons, but this robs wing locker space.
Ownership is relatively simple and the plane is reliable. I have not had an airframe-specific item ground me. The only failures that have caused delays for me are engine related, but that can happen on any plane. Concerns with landing gear are exaggerated so long as its properly cared for. Parts availability has been good and costs are reasonable if you dont mind buying used ones, in some cases. There are items (most notably the nose gear trunion) that do have high costs. The only maintenance oddity Ive had has been needing to replace a decent number of rivets, primarily on the wings. I dont know how much of this has to do with the Colemill engine conversion (and the resulting increased speed), however the cost for these rivets to be replaced is minimal and at no point does it create a structural concern. Despite having over 8000 hours on the airframe, this plane is doing well.
The market tends to favor 310R models, being the newest in the fleet and also having the larger aft cabin, nose baggage, plus the only 310 with FIKI. Their extra length can make hangaring more challenging. The resale value of R models has been going up recently, a testament to the capability and value of the 310.
Last, a 310 is not difficult to fly, but potential owners must make a commitment to both initial and recurrent training.
Cloud Nine Rescue Flights
Since 1981, Ive owned four 310s, two of them being the R model owned in the 1980s, one of them being a 57 model owned in the 1990s, and the 1956 model I own now, N5267A, and pictured. I also helped manage and flew a 310R from 2000 to 2009 for two non-pilot business partners.
I admit I am partial to the straight tail classics. Why the 310? With the R model, my wife and I, along with our two 200-pound sons, and 200 pounds of luggage and SCUBA gear flew nonstop to a dive location over 500 miles away in just over three hours and still had 1.5 hours of fuel left for full cruise power.
My 1956 model can easily handle four full-sized adults, each with a typical airline-legal carryon suitcase, and go 400-plus NM with IFR reserves. With just me and my wife, we can take all the gear we want, plus fill the auxiliary tanks and easily add another 200 NM to that nonstop range.
My R models typically trued out in the 180- to 190-knot range, with chock to chock fuel burn rates of around 25 GPH. My 1956 model regularly trues out at 170 to 173 knots while showing a block fuel consumption of 21 GPH. Any 310 is a rock-solid flying machine, great on instruments and a nice short field performer, especially with VGs.
The biggest mistake first-time legacy twin buyers make is thinking that just because these planes can be bought for nearly a song, that they will be equally cheap to operate. Parts and labor will be as much, if not occasionally more, as a $1.3 million new Baron. You must also build your support network of mechanics who truly know the airframe. And as with most other legacy GA aircraft in todays market, what you invest in it now wont be what you realize on resale. But when you consider that for under $100,000, you can have a showpiece 310 that will run with new birds costing seven to ten times as much to buy, that resale depreciation point is moot.
If you go into 310 ownership with the mindset that you are spending this money on the airframe and upgrades because its what you want now, rather than worrying about the next owner and resale, then you will be rewarded with many years and flying hours of what I think is one of the best and most plentiful twins general aviation ever offered.
Guy R. Maher
Cleveland, North Carolina