Cessna 310

Cessna entered the light-twin market a clear overdog in late 1954. Piper's Apache had come onto the scene about a year earlier, but with only 150 horsepower a side. Not only did the 310 start out a strapping young twin, but it lived a long and fruitful life, finally surrendering to old age and declining market share in 1981. Through its 28-year production span, the 310 evolved from a five-seater with pressure-carbureted engines to a high- flying turbocharged six-placer with known-icing certification. Cessna's landmark twin also begat a larger turbocharged model, the 320, in 1963, and provided the basis for the pressurized 340.

Thanks to the long life of the airplane and the many changes made to it, an almost bewildering array of choices exist for the 310 buyer. For the budget-minded, an early 310 can be a (relatively) inexpensive entry to the world of twin engines. Maintenance concerns and the inexorable march of time — these first 310s are 40 years old now, after all — can make the purchase of the 1950s and 1960s models chancy. If you have a hankering for old and complex airplanes, the 310 might well fit the bill, so long as you know that the initial maintenance bills can be thrilling. Remember, also, that the cost of maintaining an airplane like the 310 is keyed more to its health and the price of parts than the purchase price.

At the other extreme of the line, the last models of the 310 can be counted on to perform transportation duties with the capability of newer models, and the prices reflect this ability.

One of the earmarks of the line's changes concerns horsepower. Starting with pressure-carbureted 240-hp O-470 Continentals, the 310 gained real fuel injection and an additional 20 hp per side with the C model, in 1959. Several variants of the IO-470 were used through the 1975 model year in the 310Q. General opinion of the IO-470 has always been good, and it seems the model has performed quite well in the 310. According to owners and mechanics, the 470s live a long and happy life under 310 cowls, and the number of service difficulty reports slated for the 470-powered airplanes is proportionally lower than for the IO-520 and TSIO-520 versions. The bigger Continental came aboard in the 1975 model, the R. It's interesting to note that through the life of the 310, engine power was increased only 45 hp a side. Compare this to the Beech light twins, which began with 180-hp Lycomings in the Travel Air and culminated (imploded, some say) with a pair of turbocharged 380-hp monsters in the 56TC.

Other variations on the 310 theme will tip you off to the airplane's age. Yes, we're talking tuna tanks, those slightly clunky vessels at the ends of the wings, slated to hold 50 gallons of fuel each. (Such nicknames come from the tank's fish-like profile.) The tip tanks became twin Cessna hallmark. So-called "Stabila Tips," with an upward cant, arrived with the 1963 G model. Presumably, the canted tanks were to improve lateral stability by imparting additional wing dihedral. And the 310 needed help in this department, what with 300 pounds of avgas way out there on the wing. You could say that it has substantial roll inertia.

As Cessna did to virtually all its models in the late 1950s and early 1960s, the 310 received a swept vertical fin in place of the upright tail used through the 1959 model. At the other end of the airplane, the 310 nose grew, Pinocchio-like, through the decades, making a big leap with the 1975 R model. In the midst of all this, the cabin was enlarged, and the model became a six-seater with the 1963 310H. Windows were added and lengthened through the 310's gestation as well.

Another significant change came with the 1964 I model: The overwing augmenter tubes gave way to conventional exhaust plumbing. Pulsing exhaust gases in the augmenters were supposed to create a suction of cooling air through the cowling, on the premise that at high power, more suction would be created and therefore cooling would be improved. And although the system worked, exhaust gases, being quite corrosive, wreaked havoc on the wing structure. Many early 310s suffer substantial corrosion at the aft spar and wing skins, and such trouble unnoticed during the prepurchase inspection can leave the new 310 owner feeling a bit blue.

Flying the Cessna 310 is, on the other hand, a pleasure. One of Cessna's great triumphs through the decades has been the success in making transitions up through the line relatively painless for pilots. That means the 310 flies like other Cessnas, with the caveats about its greater weight and speed taken into account. Pitch response is heaviest, roll the lightest, with generally good stick force per G and longitudinal stability. Pilots coming from other light twins will recognize the 310's as a large step up; it feels like a much larger, more substantial airplane than, say, an Apache or Travel Air. As for those moving up through the Cessna line, a 210 pilot will most definitely notice the 310's heavier controls, higher wing loading, and greater approach and landing speeds. It is a bigger jump from the complex single into the 310 than it is for, say, a pilot moving from a Bonanza to a Baron.

In the single-engine category, the 310 also performs reasonably well, however few light twins are truly spectacular with one engine inoperative. Early 310s could manage 415 feet per minute on one engine at maximum gross weight (4,700 pounds in the 310B). As the maximum weights increased, the single-engine climb rate decreased; the T310R, at its 5,500-pound maximum, is supposed to ascend at 390 fpm at sea level with one feathered. Single-engine service ceiling went up with the turbo models, to 17,200 feet in the T310R; a 310B could hold 7,700 feet on one engine.

If there's an aspect of the 310's handling qualities likely to catch a novice pilot out, it is single-engine procedures near the runway. For one thing, the all-electric gear is not particularly quick to stow. This coupled with the natural rolling tendencies caused by the tip-mounted fuel tanks, can make for a busy few moments immediately following engine failure. Experienced 310 pilots say that minimizing aileron inputs is the only way to prevent the 310 from rocking around the pattern like a rowboat in high seas. In general terms, the 310's a sweetheart, a veritable immovable object on instruments and a good, if somewhat stiff, rider in turbulence. Another tip from the 310 experts: To offset the nose-up pitching moment upon deploying the split flaps, select gear-down simultaneously. Drop the wheels and 15 degrees of flap, and the pitch changes will cancel each other out.

Speed has always been a strong 310 selling point, for good reason. With the 240-hp engines, the 310 will turn in cruise speeds of 183 knots (70-percent power at 7,500 feet, burning 25 gallons per hour total) and climb with both engines at better than 1,600 fpm from sea level. More weight in later models about makes up for the extra power: A 260-hp-a-side Q model turns in 186 knots (71 percent at 7,500 feet, on 26.5 gph) and climbs at 1,495 fpm; not bad considering the Q's 600-pound higher maximum gross weight. Finally, the 285-hp versions will do just over 190 knots on 29 gph.

Naturally, the turbocharged 310s are the quickest, showing 198 knots at 10,000 feet (on 74 percent and 31 gph) and 220 knots at 20,000 feet with the same settings. All the T310s come with Garrett turbochargers and automatic wastegates and are conservatively boosted. Where some versions of the TSIO-520 have been pushed to 325 hp, the 310's engines are practically loafing at 285 hp. Maximum boost for a sea-level takeoff is a moderate 32 inches. However, the turbos are relatively small, and power is down to 55 percent by 25,000 feet at the maximum recommended cruise rpm of 2,350. Operators say the T310s work best in the high teens.

Although the engine-compartment systems of the various 310s are fairly straightforward, the same cannot be said for the fuel system. It all started innocently enough, with those 50-gallon tip tanks as the only containers of fuel. Designed to shear off in the event of a crash, the tips were the only tanks until the 1958 B model. Then Cessna installed auxiliary tanks in the wings, good for an extra 40 total gallons. Wing locker tanks, each with 20 gallons total capacity, became options with the 1967 models. You could order one or both of the locker tanks. Finally, the auxiliary tanks were enlarged once more, in 1973, to 63 gallons total. Together, this means that 310s came with total capacities of 100, 140, 163, 183, or 203 gallons. A long-range airplane has six tanks and 10 fuel pumps.

Confused? Wait until you have to manage the tanks. Two main traps await the unwary 310 driver. First, all 310s suck more fuel from the tanks than the engines will use; both the pressure carburetor and fuel injection models have a return line from the engine compartments. However, this connection returns fuel only to the main tank on the same side as the engine. This means that using fuel from either the auxiliary tank on the same side, or the main tank on the opposite side, about half the fuel flow will be moving to the same-side main. When the main reaches capacity from the return fuel, any excess is sent overboard, and you can't cross-feed auxiliary fuel. Second, is the locker-tank scheme. Most airplanes have just one of these, and its contents cannot be consumed directly by the engines. Instead, locker fuel must be pumped to the corresponding main tank. So if you have a right-side locker, you will have to draw down the right main by at least 20 gallons to make room for the locker fuel and then crossfeed the left engine to minimize lateral imbalance from those extra 120 pounds now out on the right wing tip.

Three-ten shoppers (and pilots) would do well to sit down with a jug of coffee and a good reading lamp and bone up on this airplane's fuel system.

We also sat down with a warm stack of service difficulty reports and discovered that the 310's gear system is, quite literally, its Achilles' heel. Out of 225 SDRs (for about 150 different airplanes), we counted more than 40 regarding the gear alone. Maladies include broken or cracked mounts, support structures, actuator rods, door hinges and actuators, shock struts, and bellcranks. We noted several cases of full or partial gear collapse thanks to parts failures. More than half of the reports target the main gear. This lesson ought to be clear: Carefully and thoroughly inspect the gear system on any 310 considered for purchase. Also, consider it a bonus if the airplane is fitted with retrofit Cleveland brakes; the original Goodyears are known to be somewhat troublesome and expensive to maintain.

According to owners and 310 support groups, parts are readily available for the airplane, although, as is true with any model these days, the costs can be dear. Fortunately, aside from the gear troubles noted earlier, there doesn't seem to be any one recurring trouble spot with the 310s. That's actually a bit amazing, considering the overall age of the fleet and the complexity of the machines.

Cessna 310: Still the Sky King?
Marc E. Cook, AOPA Pilot, May 1994

The 310 is an all metal, four/six-place, low wing, twin engine airplane and is equipped with retractable tricycle landing gear.
This airplane is certificated in the normal category. Spins and aerobatic maneuvers are not permitted in normal category airplanes. The airplane is approved for day and night VFR/IFR operations when equipped in accordance with F.A.R. 91 or F.A.R 135.

The airplane is powered by two horizontally opposed, six cylinder, direct drive, normally aspirated, air cooled, fuel injected engines. The engines are Continental Model IO-520-Ms and are rated at 285 horsepower each.

The fuel system consists of two main tanks, two optional auxiliary tanks, two optional wing locker tanks, fuel selectors for selection of main, auxiliary or crossfeed and other necessary components to complete the system. The main tanks are integrally sealed aluminum tanks mounted on each wing tip and each contain an auxiliary fuel pump and transfer pump. The optional auxiliary tanks are available in two sizes. These tanks are bladder-type cells located between the spars in the outboard wing. The optional wing locker fuel tanks are located in the forward portion of each wing locker baggage area. These tanks are bladder-type cells which supplement the main tank fuel quantity. Each engine is equipped with a mechanically driven fuel pump which provides fuel to the metering unit. A fuel flow gauge, fuel quantity gauge, and a fuel low level warning light are located in the cockpit.

The airplane has a 28-volt, negative ground, direct current electrical system powered by an alternator on each engine and a 24-volt battery.