Cessna 337 Skymaster

The Cessna 337 Skymaster is one of the most visually distinctive general aviation twins ever produced — a high-wing, twin-boom, six-seat utility aircraft with two engines mounted in a push-pull centerline-thrust configuration. One engine pulls from the nose and one pushes from the rear of the fuselage pod, eliminating the asymmetric yaw that defines a conventional twin engine-out scenario. The FAA recognized this unique handling by granting the Skymaster its own "centerline thrust only" class rating, allowing pilots to earn a multi-engine privilege restricted to Skymaster-style aircraft without ever demonstrating conventional Vmc work.

The Skymaster lineage began with the fixed-gear Model 336 in 1964, followed by the retractable-gear Model 337 Super Skymaster introduced for the 1965 model year. Production continued through 1982, with approximately 2,993 civilian airframes built (including 332 pressurized T337G/P337 variants) plus 513 military O-2 Skymasters used extensively by the USAF as forward air controllers in Vietnam. The O-2 served into the 1990s and cemented the Skymaster's reputation as a rugged, stable observation platform.

The Skymaster attracted a devoted, somewhat contrarian following: pilots who valued the benign engine-out handling, the panoramic high-wing visibility, the wide utility cabin with clamshell rear doors, and the distinctive look. Detractors point to the rear-engine cooling quirks, the cramped cowlings that make maintenance labor-intensive, and the somewhat anemic performance compared to conventional twins of similar horsepower. Approximately 1,200 Skymasters remain on the FAA registry, supported by the Skymaster Owners And Pilots organization and a concentrated ecosystem of specialist shops. The type shares a parts-support challenge with other orphaned Cessnas — parts are available but require knowing where to look. See also cessna-310-320 for the conventional Cessna twin comparison.

Recommended sweet spot: The 337G (1973–1977) is the preferred non-pressurized variant — it replaced the troublesome 1965–1972 hydraulic landing gear and complex fuel system with simpler, more reliable alternatives. The P337H (1978–1980) represents the peak of the line for high-altitude capability. Avoid the early 336 (fixed gear, underpowered) and early 337–337F airframes unless priced accordingly for their fuel and gear system headaches.

The Skymaster's 169 KTAS cruise on 420 total HP is slower than a comparable conventional twin — a 310R makes 185 KTAS on 570 HP but burns 28 GPH to the 337's 22 GPH. The drag penalty of the twin-boom configuration and the push-pull fuselage is real, and book numbers of 160–170 KTAS translate to roughly 155–165 KTAS at typical cruise power settings in the real world.

Rear engine cooling: The single most discussed performance quirk. The rear engine is fed by a dorsal air scoop and relies on large cowl flaps and carefully maintained baffling to stay within CHT limits, especially during prolonged climbs and hot-day ground operations. Properly rigged aircraft with healthy baffling do not overheat; neglected examples routinely exceed CHT limits on the rear engine, accelerating cylinder wear. A specific departure profile — shock cooling avoided, climb airspeed kept up, cowl flaps managed deliberately — is part of the type transition.

Turbocharged variants: The T337 and P337 use TSIO-360 engines producing 225 HP flat-rated well into the mid-teens. Critical altitude is approximately 20,000 ft, enabling 180–190 KTAS TAS in the high teens. The P337 adds 3.35 psi pressurization differential — modest by modern standards but sufficient for an 8,000 ft cabin at 20,000 ft, meaningfully reducing the fatigue of long high-altitude legs.

Engine-out handling: With thrust aligned along the fuselage centerline, losing an engine produces no yaw — just a reduction in available power. There is effectively no Vmc in the conventional sense (published Vmc of 65 KIAS is a bookkeeping speed; there is no critical engine). Pilots gain the margin of the second engine without the training burden of conventional asymmetric-thrust emergencies. The catch: the rear engine failure at takeoff is not always immediately obvious, and Skymaster accident history includes takeoff accidents where the pilot did not realize the rear engine had failed until the aircraft refused to climb. Pre-takeoff run-up procedures must verify both engines are making rated power.

Climb and ceiling: The NA 337G climbs at 940 FPM at sea level and has an 18,000 ft service ceiling on both engines. Single-engine climb rate is approximately 370 FPM (front engine only) or 235 FPM (rear engine only) — the front engine provides slightly better single-engine performance due to prop efficiency in clean air. Single-engine ceiling is approximately 7,000 ft NA, 12,000+ ft for the turbocharged variants.

Standard fuel load (90 gal, 540 lbs):

• Max gross weight: 4,630 lbs
• Empty weight: 2,925 lbs
• Fuel: 540 lbs
• Remaining for payload: 1,165 lbs
• Practical occupancy: 4 adults (680 lbs) + 400 lbs of bags/cargo, or 5 adults (850 lbs) + 300 lbs bags

Full seats, reduced fuel (6 adults + bags):

• Pilot + 5 pax: ~1,020 lbs
• Baggage: 200 lbs
• Total payload: 1,220 lbs — slightly over the full-fuel payload budget
• Fuel available: 1,705 − 1,220 = 485 lbs = ~81 gal (just under full fuel)
• Range at 65% power (~22 GPH): approximately 550–600 NM with IFR reserve

Full fuel + 2 crew configuration (long-range cruise):

• Pilot + copilot + bags: 420 lbs
• Full fuel: 540 lbs
• Total used: 960 lbs (well under 1,705 useful)
• Range at 55% economy cruise (~18 GPH): approximately 1,100+ NM with reserve

P337H altitude advantage: The pressurized P337H cruises efficiently at FL180–FL200 at approximately 180 KTAS on 22–24 GPH total. The 3.35 psi differential maintains an 8,000 ft cabin at FL200, reducing passenger fatigue on long legs. For two-to-three-person business travel over weather, the P337H is the most capable aircraft in the family.

Practical limitation: Unlike the cessna-310-320, the Skymaster is a legitimate "full seats plus meaningful fuel" aircraft at short-to-medium ranges. The useful load distribution favors people-hauling over fuel-loading. For surveying, observation, and 4–5 passenger regional trips, it is genuinely a full-cabin airplane.

For comparison with the conventional Cessna twin, see cessna-310-320. For the next-size-up pressurized twin, see cessna-340 (if available) and the cessna-414-421 family.

See business-travel, cross-country, surveying, flight-training, cargo-hauling.

Cross-Country (Score: 8/10): Strong cross-country tool. 1,139 NM range at economy cruise, true IFR capability, and the engine-out security for hard IFR legs over inhospitable terrain. The P337 extends capability into the flight levels for weather avoidance and tailwind harvesting. Slower than a 310 or Baron, but meaningfully cheaper to fuel.

Business Travel (Score: 7/10): A capable business platform for operators who value twin redundancy without the conventional-twin training overhead. Six-seat cabin with clamshell doors is the easiest cabin to board of any light twin. Modest 169 KTAS cruise makes it slower than competing twins, which matters on 500+ NM legs. The P337H is the business-travel sweet spot in the family.

Surveying (Score: 8/10): Exceptional surveying and observation platform — the military O-2 mission was exactly this. High wing provides unobstructed downward visibility, twin-engine redundancy for extended patrol operations, moderate fuel burn, and slow-flight capability from the 60 KIAS stall. Used extensively for aerial survey, pipeline patrol, law enforcement, and border operations. One of the few civilian aircraft where the Skymaster is the best tool for the job.

Cargo Hauling (Score: 5/10): 1,705 lb useful load is respectable, and the optional belly cargo pack (337B onward) adds ~300 lbs of external capacity for bulky freight. Clamshell rear doors ease loading. However, cabin volume is modest compared to dedicated haulers like the cessna-205-206-stationair, and the rear engine occupies space that a conventional twin would use for baggage.

Flight Training (Score: 5/10): Unique niche as a multi-engine trainer for pilots who want the "centerline thrust only" restricted rating — cheaper to earn and insure than a conventional multi-engine add-on. Poor as a primary or Vmc trainer because there is no conventional Vmc work. Some flight schools used Skymasters historically for this purpose; the market is small today but the role persists.

Backcountry (Score: 3/10): High wing and 700 ft landing ground roll suggest possibilities, but the low-slung rear engine and prop clearance limit unimproved operations. Some operators have used Skymasters on improved dirt strips; serious backcountry work belongs to cessna-185-skywagon or a Maule.

Local Fun Flying (Score: 4/10): Two engines to feed and maintain, annual inspections that run $12,000–$16,000, and a specialist mechanic requirement make the Skymaster an inefficient local-flying platform. Owners who fly frequent long trips amortize the fixed costs; occasional flyers do not.

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

The Skymaster fleet spans 1964–1982 with panel configurations ranging from original ARC radios through modern glass retrofits. Because the Skymaster is a niche twin, shops with installation experience are concentrated — expect to travel to a Skymaster specialist for complex installs. See avionics-pricing.

Budget tier ($0–$15,000): Legacy King KX-155/KX-165 nav/coms, KT-76/KT-78 transponders, KAP-150 or KFC-200 autopilots. ADS-B Out compliance via minimal GTX-335 install. Serviceable VFR and basic IFR, but parts support for the old ARC/King gear is shrinking.

Mid tier ($15,000–$45,000): Garmin GTN 650Xi or 750Xi navigator, GTX-345 transponder with ADS-B In, Garmin G5 attitude/HSI pair, audio panel upgrade. This package brings a 1970s Skymaster into contemporary IFR capability for well under six figures.

Premium tier ($45,000–$100,000+): Garmin G500 TXi primary flight display, dual GTN 750Xi navigators, GFC 500 or GFC 600 digital autopilot (STC availability for the 337 is more limited than for the 310 — verify STC coverage), engine monitoring for both engines (JPI EDM-760 twin or Electronics International MVP-50T). Rear-engine monitoring is especially valuable given the cooling concerns; a quality twin engine monitor is arguably the best single upgrade a Skymaster owner can make.

Panels in the wild: A 1976 337G in the mid-$130,000 range typically carries a GTN 650 + G5 + GTX-345 combination with legacy autopilot. Fully glass Skymasters are rare and command top-of-market pricing.

Riley Super Skyrocket Conversion — The most famous Skymaster modification. Riley Aircraft's P337 conversion replaced the 225 HP TSIO-360 engines with 310 HP Continental TSIO-520s, added intercoolers, three-blade propellers, and air conditioning. The resulting Super Skyrocket climbed at 2,500 FPM and cruised 220+ KTAS. Riley Aircraft went into bankruptcy in 1996; STCs passed to SuperSkyrocket LLC and are now held by Kasper Industries. Converted airframes command significant premiums but parts for the Riley-specific components are difficult to source. Installation is not currently offered as a new conversion.

Robertson / Sierra STOL Kit — Leading-edge cuff, aileron gap seals, and flap modifications. Reduces stall speed by approximately 10 knots and improves short-field performance. Most visible identifier is extended dorsal fins along the tail booms. Install cost historically $25,000–$40,000; rarely seen on civilian 337s.

Micro Vortex Generators — Lower-cost alternative to the full STOL kit. Reduces VS1 by ~8 KIAS and improves slow-speed handling. Install cost approximately $2,500–$3,500. Common upgrade on surveying and observation airframes.

Flint Aero Auxiliary Fuel Tanks — Adds range through tip-mounted auxiliary tanks. Useful for ferry operations and long patrol missions.

Intercoolers (various) — Retrofit intercooler kits for turbocharged variants reduce induction air temperatures, lower CHTs, and extend engine life. Particularly valuable on the P337 for which rear-engine cooling margin is tight. Install cost approximately $6,000–$10,000.

Rear engine cooling modifications — Various third-party baffling improvements, cowl flap augmentations, and cylinder cooling enhancements target the Skymaster's recurring hot-rear-cylinder complaint. Pay attention to which specific cooling mods an aircraft has received during pre-buy.

See maintenance-ecosystem for the broader framework.

Parts availability (Fair): Continental IO-360 and TSIO-360 engines remain supported, with Air Power Inc. and Continental offering modern replacement variants (IO-360-CB, IO-360-GB, IO-360-HB, TSIO-360 variants) for the original part numbers. Airframe parts are more challenging: Cessna no longer supports the 337, and aftermarket supply depends on specialty vendors like Cessna Skymaster Mods & Parts, Preferred Airparts, and Dodson's International. Skymaster-specific components (gear doors, dorsal scoops, cowlings) often come from salvage yards. Expect parts lead times to exceed those for conventional Cessna twins.

Mechanic familiarity (Specialist): The Skymaster's cramped fuselage pod, rear-engine accessibility challenges, and quirky systems reward a shop that works the type regularly. The Skymaster Owners And Pilots (SOAP) community maintains a shop and mechanic directory. A first-encounter A&P on a Skymaster will spend significant time researching access procedures and specialty tools. Labor hours on routine annual inspections can reach 37–50+ hours for the airframe alone, before engine work.

Annual inspection cost: Expect $12,000–$16,000 for a clean, well-maintained 337G at a competent shop. First-year annuals on acquired or neglected aircraft frequently reach $20,000–$30,000 as deferred items surface. Owners report annuals stretching to six months at specialty shops waiting for parts.

Major cost items:

• Engine top overhaul (rear cylinder): $8,000–$15,000 (a recurring item on neglected airframes)
• Full engine overhaul: $30,000–$45,000 per engine
• Exhaust system (rear engine): $4,000–$8,000
• Landing gear overhaul: $4,000–$7,000
• Janitrol combustion heater overhaul: $3,000–$5,000
• Paint (strip and repaint): $18,000–$30,000

Estimated total annual cost (100 hours/year, 337G): $26,000–$32,000 including fuel (~$11,000), insurance ($4,500–$6,000), hangar, annual inspection, and a realistic maintenance reserve. The P337H runs $32,000–$40,000 reflecting higher insurance, pressurization maintenance, and turbocharged engine reserves.

See valuation-methodology for the full framework.

Key value drivers:

• Variant and year: 337G (1973–1977) and 337H (1978–1980) command the strongest non-pressurized market due to simplified fuel and gear systems. P337H is the top of the non-Riley market. Pre-1973 337A–F variants sell at significant discounts.

• Engine time: TSIO-360 TBO is 1,400 hours; IO-360 TBO is 1,500 hours. Mid-time engines on both sides are worth roughly $20,000–$30,000 each over run-out engines. Overhaul cost per engine is approximately $30,000–$40,000 for the NA IO-360 and $35,000–$45,000 for the TSIO-360.

• Avionics: GTN 750 + twin engine monitor + GFC digital autopilot package adds $30,000–$50,000 versus legacy panels.

• Rear engine history: Documented rear-engine cooling compliance (baffle inspections, CHT monitoring, good top-overhaul history) is a tangible value driver.

• Riley conversion: A Riley Super Skyrocket P337 typically commands a $40,000–$80,000 premium over a standard P337, but the buyer inherits parts-supply risk for the Riley-specific components.

• Paint and interior: Cosmetic restoration adds $10,000–$20,000 of perception value on a Skymaster because nice examples are scarce.

Price tiers (2025–2026 market):

Critical ADs:

• Exhaust System AD (Cessna 300/400 series, including 337) — Requires repetitive inspections and replacements of exhaust system components. The Skymaster's rear engine exhaust is particularly exposed to heat-cycle fatigue and is a recurring maintenance item. Verify compliance and recent inspection history.

• Wing Spar / Wing Skin AD — FAA AD documents for Cessna 337-series airplanes cover inspection of wings for internal and external damage, with particular attention to cracks in upper wing skins on aircraft modified with certain STCs (notably heavy STOL and Riley conversions). Review carefully if considering a modified airframe.

• Fuel Strainer Standpipe AD — Requires measuring the visible length of standpipe in the fuel strainer assembly and replacing units that fall out of tolerance.

• Vented Fuel Cap AD — Specifies fitting the Cessna MESL ME 78-47 vented fuel cap.

Common pre-buy red flags:

• Rear engine condition: Cylinder compressions and borescope inspection of the rear engine are mandatory. Historical cooling neglect accelerates wear; weak cylinders on the rear engine are the single most common pre-buy finding. Budget for near-term rear-engine top overhaul on any aircraft with marginal compression.

• Fuel system (pre-1973 aircraft): Early 337s had a complex multi-tank fuel system with awkward tank selector logic that was replaced in 1973 with a simpler system. Early-system aircraft carry operational quirks and higher maintenance exposure — budget accordingly or focus on 1973+ 337G/H airframes.

• Landing gear (pre-1973 aircraft): Original hydraulic landing gear was shared with the Cessna 210 and carried the same complexity. Replaced in 1973 by a simpler electro-hydraulic system. Pre-1973 gear is a recurring squawk item; verify recent overhaul history.

• Filiform corrosion (1977+ Imron paint): When Cessna switched to DuPont Imron paint in 1977, an epidemic of filiform corrosion followed, especially on aircraft based in warm, humid coastal environments. Inspect carefully under the paint on 1977–1982 airframes.

• Exhaust corrosion and heat damage: Rear engine exhaust runs through the fuselage pod structure. Heat-related corrosion, soot deposits, and cracked exhaust components are recurring findings.

• Landing gear door rigging: The Skymaster's gear doors are complex and prone to rigging drift. Mis-rigged doors are a common squawk.

• Vacuum and combustion heater: Like other Cessna twins of the era, the Janitrol combustion heater is a recurring annual-inspection item and CO hazard.

See insurance-underwriting for the broader framework.

The Skymaster occupies a centerline thrust twin category that is unusually favorable for a retractable-gear twin. Because the FAA recognizes a separate "centerline thrust only" class rating, pilots can earn multi-engine privileges in the Skymaster without demonstrating conventional Vmc minimum-control work, and insurers price this reduced training burden accordingly.

Typical annual premiums (2025–2026):

• Liability only, experienced pilot: $450–$700/year
• Hull + liability ($100,000 hull, $1M/$100K liability), well-qualified pilot: $3,500–$5,500/year
• Hull + liability ($150,000 hull), lower-time pilot with centerline-thrust add-on: $5,500–$8,000/year
• P337H with higher hull values ($175,000–$225,000): $6,000–$9,000/year

Pilot qualifications insurers look for:

• Private Pilot with instrument rating strongly preferred
• Centerline thrust-only rating acceptable for most underwriters
• Minimum 10–25 hours dual in type for transition pilots
• For P337/T337 pressurized variants, additional high-altitude/pressurization sign-off
• Full multi-engine rating preferred but not strictly required

Underwriting quirks:

• The centerline thrust category is sometimes confused with conventional twin categories; confirm your broker understands the distinction.
• The post-2020 contraction in piston twin underwriters hit the Skymaster less severely than it hit conventional twins, because the safety record (absent the asymmetric-thrust loss-of-control accidents) is relatively clean.
• Aircraft with Riley conversions are underwritten as modified airframes and may require specialty carrier placement.