Cessna 310/320 Skyknight

The Cessna 310 is Cessna's first twin-engine production aircraft and one of the most recognizable piston twins ever built, defined by its distinctive swept tail and signature wingtip fuel tanks — the "tuna tanks" on early models, replaced with canted stabila-tip tanks from the 310G onward. Produced from 1955 through 1980 with over 5,700 airframes completed, the 310 established Cessna as a serious contender in the light twin market and served as the foundation for all of Cessna's subsequent twin-engine designs.

The 310 debuted with the United States Air Force as the L-27A (later U-3A "Blue Canoe") before entering civilian service. Its six-seat cabin, 175–190 KTAS cruise range, and twin-engine redundancy targeted the same pilot demographic that today flies a Cirrus SR22 or Beechcraft Bonanza but wants the security of a second engine for serious cross-country and instrument work. The airplane earned a devoted following and a reputation as a "poor man's Learjet" for its sleek, fast lines.

Approximately 2,600 Cessna 310s remain on the FAA registry, supporting a robust ownership community centered around the Twin Cessna Flyer Association and Cessna Flyer Association.

The Cessna 320 Skyknight is the turbocharged sibling, produced from 1962 to 1968 alongside the 310. It used Continental TSIO-470-B (260 HP) engines in early 320 through 320C variants and upgraded to TSIO-520-B (285 HP) in the 320D through 320F. The 320 was effectively replaced when Cessna began offering the T310P/Q/R turbocharged variants of the 310 itself from 1969 onward. Total 320 production reached approximately 577 aircraft.

Recommended sweet spot: The 310Q or 310R (1970–1980) for normally aspirated; T310R (1975–1980) for turbocharged. These offer the best cabin, systems, and parts commonality with the most support infrastructure.

The 310R's 185 KTAS at typical cruise (65–75% power) is competitive with the Beechcraft Baron 55 and Piper Seneca series, with the turbocharged T310R capable of true 210–220 KTAS at altitude when conditions allow. Real-world owners frequently report 175–185 knots at 65% power on the normally aspirated model, with chock-to-chock fuel burns of 24–28 GPH at cruise.

Climb: With both engines developing full power, the 310R climbs at 1,662 FPM at gross weight from sea level — excellent for the class. Single-engine climb rate drops to 372 FPM at sea level for the normally aspirated 310R. Single-engine service ceiling is approximately 7,400 ft MSL for the NA version and approximately 17,200 ft for the T310R — a critical difference in mountainous terrain.

Density altitude sensitivity: The normally aspirated 310 loses climb performance rapidly above 8,000 ft. Operators in high-elevation regions (Rockies, Sierras) should consider the T310R for the single-engine terrain clearance margin. The T310R's flat-rated turbocharged engines maintain full power to the critical altitude, making it a meaningfully different airplane in this regard.

Fuel system complexity: Later 310R aircraft with factory nacelle tanks and wing lockers can carry up to 203 gallons total, enabling 1,100+ NM range at economy cruise. However, the multi-tank system requires meticulous fuel management: up to eight fuel pumps and ten drain points on a fully optioned aircraft. Crossfeed procedures must be flown precisely. Pilots transitioning from singles should budget additional training time on the 310's fuel system.

Vmc awareness: Vmc is 80 KIAS, meaningfully close to the stall speeds in some configurations. The 310R's counter-rotating propellers (standard from the 310Q) eliminated the critical engine, reducing Vmc concerns on engine failure compared to earlier models without counter-rotating props.

Landing: Max landing weight is 5,400 lbs, 100 lbs below MTOW, so fuel burn prior to landing may be necessary on full-gross departures.

Standard fuel load (163 gal, 978 lbs):

• Max gross weight: 5,500 lbs
• Empty weight: 3,603 lbs
• Fuel: 978 lbs
• Remaining for payload: 919 lbs
• Practical occupancy: 2 adults (380 lbs) + bags (100 lbs) = comfortable; 4 adults (680 lbs) + minimal bags possible

Full seats, reduced fuel (4 adults + bags):

• Pilot + 3 pax: ~680 lbs
• Baggage (moderate): 120 lbs
• Total payload: 800 lbs
• Fuel available: 1,097 lbs = ~183 gal (within capacity)
• Range at 65% power (~25 GPH): approximately 700–750 NM with IFR reserve

Maximum range configuration (nacelle tanks, 203 gal, 1,218 lbs fuel):

• Useful load constraint: 1,897 lbs
• Fuel: 1,218 lbs
• Remaining payload: 679 lbs (pilot + 1 pax + baggage)
• Range at economy cruise (22 GPH): approximately 1,100+ NM

T310R altitude advantage: The turbocharged variant burns fuel more efficiently at FL200–FL230 where true airspeed climbs above 200 KTAS. A T310R at FL200 with 75% power burns approximately 28 GPH total while achieving 215 KTAS — significantly better fuel efficiency per nautical mile than the NA version at lower altitudes. For full-fuel, two-person long-legs (1,000+ NM), the T310R is the better tool.

Practical limitation: The 310 is not a "four adults plus full bags" airplane at range. Full cabin loading requires accepting significant fuel penalties and shorter legs. Realistic twin-Cessna operations are two-to-three people with baggage, leveraging the full fuel load for range — exactly the business travel mission where this airplane excels.

For comparison with the pressurized step-up, see cessna-340 and cessna-414-421.

See missions/business-travel, missions/cross-country, missions/local-fun-flying, missions/flight-training.

Business Travel (Score: 8/10): The 310's primary mission. Twin-engine redundancy for hard IFR legs, 185 KTAS cruise, and a 1,000+ NM range covering most U.S. city pairs in a single leg make it a genuine productivity tool. The six-seat cabin accommodates up to four passengers with baggage, and the 310R's lengthened nose locker adds 10 cubic feet of forward baggage. Insurance and operating complexity demand a committed, current pilot — the 310 is not a casual mission airplane.

Cross-Country (Score: 9/10): This is where the 310 earns its reputation. Fast enough to compete with some turboprops on short-to-medium legs, excellent IFR capability, and sufficient range with the optional nacelle tanks. The T310R extends capability further with altitude flexibility. A well-equipped 310R with a GTN 750 and GFC 600 autopilot is a serious coast-to-coast platform.

Flight Training (Score: 4/10): Used extensively for multi-engine add-on ratings given its ubiquity, but the 310's complexity, operating cost, and retractable gear make it a poor primary trainer. The complex fuel system and Vmc proximity require thorough systems knowledge. Fine for initial multi-engine training, poor as an ab initio platform.

Local Fun Flying (Score: 5/10): Flyable for short hops, but the operating costs ($28 GPH, two engines to maintain) make local VFR flight economically inefficient. The 310 is happiest on long legs where its speed and range advantages compound.

Backcountry/Bush (Score: 2/10): Low-wing configuration, retractable gear, and minimum 1,335 ft ground roll effectively eliminate serious backcountry operations. Some flat, improved strips are accessible, but the 310 is not a STOL machine. Robertson/Sierra R/STOL kits exist but are expensive and provide marginal improvement versus vortex generators.

Cargo Hauling (Score: 4/10): Useful load of 1,897 lbs looks generous, but full fuel (978 lbs) leaves only 919 lbs for payload — enough for four adults at standard weights with modest baggage. The 310's cabin is narrow relative to dedicated cargo platforms like the cessna-205-206-stationair.

Aerobatics (Score: 1/10): Not approved, not equipped, structurally not appropriate.

Surveying (Score: 5/10): The 310 has been used for aerial survey and patrol work due to its speed and IFR capability. Forward visibility from the low-wing platform is acceptable. Not optimized for the mission but serviceable.

The 310 fleet spans 1955–1980, so panel configurations range from early round-gauge steam with vintage ARC radios to fully glass-panel retrofits in the most upgraded examples.

Budget tier ($0–$15,000 avionics investment): Most older 310s are acquired with legacy panels — King KX-155 or Garmin SL-30 nav/com, KLN-94 or GTX-327 transponder, KFC-200 autopilot. These are flyable IFR but increasingly difficult to maintain as parts age out. Expect increasing avionics shop time as components fail.

Mid tier ($15,000–$40,000): Garmin GTN 650/750 or Avidyne IFD540 navigator replacing legacy nav/coms is the most common single upgrade. Adding a Garmin GTX-345 for ADS-B Out/In compliance and traffic awareness addresses both the regulatory requirement and situational awareness. Aspen EFD1000 or Garmin G5s for primary flight display backup are popular modernization steps without full glass commitment.

Premium tier ($40,000–$100,000+): Garmin G500/G600 TXi glass panel with GTN 750Xi navigators and the Garmin GFC 600 digital autopilot (certified for the 310R via STC) creates a near-glass cockpit in a legacy airframe. The GFC 600 replaces aging analog autopilots with LVL mode, coupled approaches, and envelope protection. Full glass retrofits in 310Rs regularly command $50,000–$100,000+ in avionics investment alone and add $30,000–$60,000 to resale value.

Common panel combinations: Many 310R buyers in the $180,000–$250,000 range find GTN 750 + GTN 650 + Garmin G5s + GTX-345 + GFC 600 to be the practical sweet spot — capable coupled approaches without the full glass price tag.

Garmin GFC 600 Autopilot — Certified for the Cessna 310R. Replaces aging analog autopilots with digital flight control including envelope protection, LVL mode, and coupled GPS approaches. Install cost approximately $25,000–$35,000. Highly recommended for aircraft used in IFR operations. STC holder: Garmin International.

Griggs Aircraft Wing Locker Tanks — STC for 18.5-gallon wing locker tanks, approved for 310K through 310R, T310P, T310Q, T310R. Up to four tanks can be installed (three if air conditioning is present), adding up to 74 gallons for a maximum of 237 gallons total. STC holder: Griggs Aircraft. Install cost varies; each tank approximately $3,000–$5,000 installed. Dramatically extends range but adds fuel management complexity.

Sierra Industries R/STOL System — Previously the Robertson STOL kit, Sierra Industries holds the STC. Full STOL leading edge cuff, aileron and flap modifications. Reduces stall speeds approximately 10 kt and improves short-field performance. Install cost is high (contact Sierra for current pricing) and many operators find vortex generators provide comparable low-speed improvements for a fraction of the cost.

Vortex Generators (Micro AeroDynamics) — STC for VG installation. Reduces VS1 by approximately 8 KIAS, improves slow-speed handling. Install cost approximately $2,000–$3,000 installed. Far better ROI than the full STOL kit.

RAM Aircraft Engine Conversions — RAM offers various Continental engine upgrade STCs for the 310 series, including cylinder upgrades and fuel nozzle improvements, primarily targeted at improving reliability and reducing CHT issues with the IO-520 family.

Air conditioning (factory option) — Several third-party STCs exist for retrofitting air conditioning on models that did not leave the factory with it. Installation is significant (cost $10,000–$20,000) and limits nacelle tank options.

See maintenance-ecosystem for the broader framework.

Parts availability (Good): Continental IO-520 and IO-470 parts remain available through multiple channels — Continental Motors, Mattituck Services, Penn Yan Express, and numerous independent shops stock common components. Cell gasket kits, cylinder assemblies, and accessory gear components are available but pricing reflects the age and complexity of the fleet. Airframe parts (gear components, door seals, trim hardware) are increasingly sourced through salvage yards and specialty vendors like Aircraft Spruce. Cessna no longer supports the 310 directly, but the aftermarket ecosystem is solid for the popular late models.

Mechanic familiarity (Common): Any A&P with twin Cessna experience can work a 310. The Twin Cessna Flyer Association (twincessna.org) maintains technical resources and a shop/mechanic directory. Dedicated 310 specialists exist at most medium-to-large GA airports. However, the 310's fuel system, gear system, and cabin heating complexity do benefit from a shop that works them regularly — a first-encounter A&P will spend more time researching than a veteran of the type.

Annual inspection cost: Expect $3,000–$8,000 for a clean, well-maintained 310R with no deferred items and a competent shop. A first-year annual on an acquired aircraft, or on a poorly maintained example, can easily reach $10,000–$20,000 once deferred items surface. Budget conservatively.

Major cost items:

• Fuel bladder replacement: $3,000–$8,000 per tank assembly (multiple tanks per aircraft)
• Landing gear overhaul (full bushing replacement): $3,000–$6,000
• Engine overhaul: $40,000–$50,000 per engine (IO-520-M); plan $45,000 as a mid-point estimate. Reserve $39–$45/hr per engine toward overhaul.
• Prop overhaul: $1,500–$2,500 per prop (three-blade) every 2,400 hours or 6 years
• Vacuum system: Legacy vacuum gyros require regular attention; conversion to electric/AHRS eliminates this risk
• Cabin heat system: The 310's combustion heater is a common squawk and potential CO hazard; annual inspection and CO detector are mandatory

Estimated total annual cost (100 hours/year, 310R): $35,000–$42,000 including fuel, oil, reserves, insurance, hangar, and a realistic maintenance budget.

See valuation-methodology for the full framework.

Key value drivers:

• Variant and year: 310R (1975–1980) commands the strongest market — lengthened nose, best systems, IO-520 engines. The T310R adds a $15,000–$30,000 turbo premium. Earlier models (pre-310G) sell at significant discounts due to obsolete systems and higher maintenance exposure.

• Engine time: The IO-520-M TBO is 1,700 hours. Engines at mid-time add roughly $25,000–$35,000 each in value versus engines at or past TBO (each IO-520 overhaul runs $40,000–$50,000). Counter-rotating prop pairs on Q/R models add value vs single-direction models.

• Avionics: A GTN 750 + GFC 600 panel can add $40,000–$70,000 to asking price versus legacy avionics. WAAS IFR capability is now essentially required for a serious IFR platform; ADS-B Out compliance (GTX-345 or equivalent) is mandatory for Class B/C airspace and should be standard.

• Bladders and fuel system: Recently replaced fuel bladders add $5,000–$15,000 in legitimate value. Ask for fuel cell replacement records.

• Gear overhaul history: A documented landing gear overhaul with bushing replacement adds real value and negotiating leverage.

• Paint and interior: Cosmetics add $5,000–$15,000 in perception value for retail buyers; sharper presentation commands the top of the market range.

Price tiers (2025 market):

Critical ADs:

• AD 2016-07-21 (Elevator Trim Hardware) — Applies to 310 through 310R series. Requires replacement and repetitive inspections of hardware securing the elevator trim push-pull rod. A disconnected trim tab can jam outside normal travel limits — a potentially unrecoverable control problem. Verify compliance before purchase.

• Icing Prohibition AD — Prompted by icing-related accidents and incidents, this AD requires either a supplemental AFM placard prohibiting known icing or specific airspeed procedure increases. The 310 is not certified for known ice in standard configuration; operators who fly hard IFR must ensure deice/anti-ice equipment (TKS or boots) is STC-approved and installed, or fly strictly clear of known icing.

• Fuel bladder AD (early models) — Early "tuna tank" models had rubber bladder issues. An AD required specific inspection procedures and modifications. Verify accomplishment on pre-1963 aircraft.

Common pre-buy red flags:

• Landing gear rigging: Approximately 80% of non-fatal Cessna 310 accidents involve the landing gear, frequently due to mis-rigging. The electric gear system uses push-pull tubes; wear on bushings and bolts progressively mis-rigs the system. The nose gear torque tube runs on exposed needle bearings that seize in corrosion. The main gear trunnion bearings are permanently dry by design. A thorough gear rig check by a 310-experienced A&P is mandatory at every pre-buy.

• Exhaust corrosion (pre-310I models): Models prior to the 310I used an overwing exhaust augmentor system that concentrated exhaust gases against the wing skin. Corrosion on wing upper surfaces and stringers is a serious structural concern on these early models. The 310I switched to an underwing system. Inspect early variants extremely carefully for exhaust-related corrosion.

• Fuel bladder aging: All 310s have rubber bladder tanks in the wing sections. Bladders age out every 15–20 years and can develop wrinkles that trap water above the drain points. A vintage 310 with never-replaced bladders is a significant maintenance liability — new or recently replaced bladders add real value. Budget $3,000–$8,000 per tank assembly for replacement.

• Fuel system complexity and leaks: Long fuel lines running from wingtip tanks, multiple pumps, and numerous fittings create many potential leak points. Inspect every fitting carefully during pre-buy. Fuel system overhaul on a neglected 310 can easily exceed $10,000.

• Spar and wing carry-through: Age-related corrosion in the wing spar carry-through is a concern on any 1950s–1960s vintage airframe. Inspect carefully; remediation costs can be substantial.

• Chrome cylinder issues (O-470 series): Early 310s with Continental O-470 engines have documented cylinder reliability issues with chrome-bore cylinders. Verify cylinder condition and history.

• Log book gaps and deferred maintenance: The 310's complexity makes annual inspections expensive; some owners defer items. Require complete, unbroken maintenance records.

See insurance-underwriting for full framework.

The Cessna 310 falls into the complex twin underwriting category. Insurers require meaningful multi-engine PIC time before providing hull coverage at standard rates, and significant total time before offering competitive liability limits. Underwriting the 310 has become moderately difficult as the pool of insurers writing piston twins has contracted post-2020.

Typical annual premiums (2025):

• Liability only, experienced pilot (1,500+ total hrs, 500+ multi): $350–$600/year
• Hull + liability ($150,000 hull, $1M/$100K liability), well-qualified pilot: $4,500–$7,000/year
• Hull + liability, lower-time pilot (500 total, 100 multi): $7,000–$12,000/year or higher; some insurers may decline

Pilot qualifications insurers look for:

• Minimum 300–500 multi-engine hours for reasonable rates (not just the add-on)
• Recent 310 or 310-type-specific checkout with an approved instructor
• Instrument currency and demonstrated IFR proficiency
• No hull losses in the prior 5 years

Underwriting quirks:

• The 310's gear-related accident history (mis-rigging) appears in underwriter actuarial models; gear-related claims are common in the 310 fleet. Some underwriters require annual gear rigging certification by a qualified A&P.
• Turbocharged T310R models may require additional endorsement or carry a slight premium over NA variants due to higher hull value.
• Non-U.S. operations (Mexico, Caribbean) require specific geographic endorsements.
• Single-pilot IFR operations are generally fine but must be disclosed.