Grumman G-21A Goose

The Grumman G-21 Goose is a twin-engine, eight-seat amphibious flying boat designed in 1937 as Grumman's first monoplane and first commercial aircraft. Originally commissioned by a group of wealthy Long Island businessmen who wanted an "air yacht" to commute between Long Island and Manhattan, the Goose quickly found a broader market with the U.S. Navy, U.S. Army Air Corps, Coast Guard, and RAF/RCAF as the JRF, OA-9, and Goose Mk.I during WWII. Of approximately 345 built between 1937 and 1945, roughly 30 remain airworthy today — most concentrated in bush/island operations in British Columbia, Alaska, and the Caribbean.

The Goose's reputation is as a rugged, seaworthy, high-capacity amphibian that flies heavier than it looks, lands harder than it looks, and costs considerably more to operate than almost anything else in general aviation. It is flown today by a mix of island air charter operators (notably in BC and the Pacific Northwest), collectors, warbird enthusiasts, and a handful of private owners who can absorb the operating cost of two Pratt & Whitney R-985 Wasp Junior radials and the maintenance burden of a 1940s-era all-metal hull. See Grumman G-44 Widgeon for the smaller four-place sibling and Grumman G-73 Mallard for the larger, more refined successor.

Frontmatter numbers reflect the baseline G-21A, which remains the most common surviving variant.

Book cruise for the G-21A is typically quoted at 175 mph (152 KTAS) at 5,000 ft; real-world operators in BC and Alaska plan 140-150 KTAS at 65% power to stay within fuel reserves for mountain/island work. Fuel burn is substantial — approximately 44 gph total at cruise and closer to 55-60 gph at full throttle — so the 220-gallon standard fuel capacity yields roughly 4.5 hours of cruise at a realistic 640 nm range with VFR reserves.

The Goose is notorious for its "personality" in the water. The hull is relatively short and the wing loading is high for a flying boat, meaning it lands hard on water and is sensitive to sea state — experienced operators limit water operations to 12-18 inch swells. On land, the narrow-track main gear and high center of gravity demand careful crosswind technique. Density altitude is a serious consideration: the R-985s are not turbocharged, and hot-and-high water takeoffs on glassy water can push the aircraft's demonstrated single-engine ceiling below the terrain. Single-engine service ceiling at gross is only about 6,500 ft, making engine-out performance over mountainous terrain a genuine concern.

The McKinnon turbine conversions (G-21E/G) fundamentally change the airplane: PT6 reliability, sea-level rated power regardless of altitude, a 12,500-lb gross weight, and a useful load north of 4,500 lb. Cruise climbs to 180-190 KTAS and single-engine performance becomes genuinely safe. They also roughly double the acquisition cost and introduce PT6 hot-section and overhaul expenses that dwarf the airframe maintenance.

With 220 gallons (1,320 lb) of fuel and a useful load of 2,575 lb, the G-21A has roughly 1,255 lb of payload with full fuel — enough for 6 adults plus light baggage on a 640 nm leg. Typical real-world scenarios:

• Full fuel + 2 crew + 4 pax + light bags: 4+ hour range, 600 nm legs, the classic "island charter" profile.
• Full 8 seats + bags: Requires fuel reduction to about 120-130 gallons, limiting range to 350-400 nm — the BC/Alaska commuter profile with shorter legs and frequent top-offs.
• Cargo configuration (seats removed): Up to 2,400 lb of cargo with 100 gal fuel, 250 nm practical range.
• McKinnon G-21G turbine: 4,500+ lb useful load, 586 gal fuel, easily carries 10 pax + bags for 700+ nm legs — a different airplane entirely.

The Goose's payload-range envelope is actually quite usable; what constrains real-world missions is density altitude (no turbocharging on the R-985), sea-state for water ops, and the ever-present fuel-burn economics that make every flight a deliberate decision.

• Backcountry/Bush (8/10): Few aircraft match the Goose for combined water, land, and payload capability in remote environments. It is the iconic BC coastal bush airplane, operated by Pacific Coastal, Harbour Air, and numerous smaller operators for 70+ years. Sensitive to sea state and unforgiving on rough water compared to a Beaver or Otter. See Backcountry / Bush Flying.
• Cargo Hauling (7/10): 2,575 lb useful load (piston) or 4,500+ lb (turbine) with a large cabin door makes the Goose a capable light freighter, particularly for island and coastal routes where land access is impossible. See Cargo Hauling.
• Local Fun Flying (6/10): For the owner who can afford it, the Goose is unmatched as a "show up anywhere" airplane — beach, lake, grass strip, paved runway. Operating cost prevents casual use.
• Cross-Country (5/10): 150 KTAS cruise and 640 nm range are respectable, but fuel burn, parts logistics, and the reality that few airports have 100LL trucks expecting 44 gph piston twins make long trips an adventure.
• Surveying (5/10): Used historically for aerial photography (OA-9/OA-13) and coastal survey; turbine variants still do this work, but modern twin turboprops and drones have largely displaced the Goose.
• Business Travel (3/10): Cabin is spacious but unpressurized, slow, noisy, and expensive per mile. The rare owner who uses one for business is making an aesthetic statement, not an economic decision.
• Flight Training (2/10): Purely multi-engine seaplane rating work at operators like The Goose Hangar (Anacortes, WA). Not a primary trainer by any stretch.
• Aerobatics (1/10): Not approved, not capable, not attempted.

Panels vary wildly by individual aircraft. Typical configurations:

• Restored working bird ($350k-600k): Legacy King KX-155/KMA-24 stack, ADF, legacy DME, mechanical gyros, round-gauge engine instruments. Marine VHF often added for water operations. Many aircraft still run 1970s-era avionics with no ADS-B compliance past 2020 — a growing squawk on pre-buy.
• Upgraded operator bird ($600k-900k): Garmin GTN 650/750, GTX 345 ADS-B In/Out transponder, GMA 35 audio panel, GI 275 or Aspen EFD1000 primary attitude, JPI EDM-760 twin engine monitor replacing the original cluster. STC paperwork for the Goose specifically is thin — most installs rely on AML STCs where the Goose is listed, or field approvals.
• Turbine conversion (G-21G, $1.2M+): Typically Garmin G500 TXi or G600 TXi, dual GTN 750, Garmin GFC 600 autopilot where approved, full PT6 engine instrumentation (often Garmin EIS), radar or Garmin GWX 75 in the radome nose, synthetic vision.

See Avionics Pricing Reference for STC and install cost references.

• McKinnon G-21C piston conversion: Four Lycoming GSO-480s, fiberglass radar nose, wraparound windshield, retractable wingtip floats, enlarged "picture" cabin windows. TC 4A24 (Nov 7, 1958). Only 2 built; historical interest only.
• McKinnon G-21D: Stretched fuselage, 12 seats, 12,500 lb gross. Extremely rare.
• McKinnon G-21E "Turbo-Goose": PT6A-20 (550 shp) or PT6A-27 (680 shp) turbine conversion, simplified structure, 10,500 lb gross.
• McKinnon G-21G "Super Goose": The definitive turbine conversion. PT6A-27, 12,500 lb gross, 586 gal fuel, all G-21C/D structural upgrades. FAA approved Aug 29, 1969 under Section IV of TC 4A24. Roughly 5-6 conversions completed.
• Antilles Super Goose: Antilles Seaplanes (Gibsonville, NC) acquired the McKinnon type certificate in the early 2000s and marketed an updated PT6A-27/-34 conversion with modern avionics. A handful of aircraft were modernized; company activity has been intermittent.
• Volpar nose gear / tricycle gear conversion: Historical STC for improved land handling on some aircraft.
• Gar-Aero wingtip tanks: Extended-range fuel pods added to many G-21A airframes, adding roughly 50-80 gallons.
• Aux fuel tanks, cargo door enlargement, and seaplane base modifications: Various field-approval mods common on BC/Alaska operator aircraft.

Maintenance is the defining cost of Goose ownership. Realistic direct operating cost is $750-1,200 per flight hour on the piston G-21A, climbing to $1,500-2,500/hour on turbine conversions.

• Parts availability: poor. No factory support. Airframe parts come from PMA suppliers, salvage, and custom fabrication. Critical structural spares (wing attach fittings, hull skins, gear components) are effectively one-off machine-shop work.
• R-985 Wasp Junior overhauls: Approximately $60,000-90,000 per engine ($120k-180k per pair) at specialty shops like AeroRecip (Winnipeg), Covington Aircraft (Oklahoma), and Radial Engines Ltd (Guthrie, OK). TBO is 1,200 hours but many operators run on-condition with frequent cylinder work.
• PT6A-27 overhauls (turbine conversions): $300,000-450,000 per engine depending on hot section vs. full overhaul, plus accessory gearbox.
• Annual inspection: $15,000-30,000 base for the piston variant in good condition, escalating rapidly if hull or wing-attach squawks are found. Major hull work on a corroded aircraft can run $150,000-300,000+.
• Mechanic familiarity: rare. A handful of shops have institutional knowledge — notably Kenmore Air (WA), Harbour Air (BC), Pacific Coastal (BC), Antilles Seaplanes (NC), and a few independent radial-engine specialists. Most A&Ps have never seen one.
• Props: Hamilton Standard 2D30 / Hartzell HC-series; overhaul $8,000-15,000 per prop.

See Maintenance Ecosystem for radial overhaul shops and vintage amphibian support ecosystem.

Price ranges reflect the enormous spread between project aircraft and turbine conversions:

• Project/non-flying G-21A: $150k-300k. Usually long-term hangar queens with corrosion issues; rebuild cost can exceed $500k.
• Flying G-21A with mid-time R-985s, legacy panel: $350k-500k.
• Nicely restored G-21A, fresh engines, modernized panel: $500k-750k. A recent listing showed a restored G-21A with 2022 AeroRecip R-985 overhauls priced near $495k; exceptional examples command more.
• McKinnon piston G-21C/D: Rare; valued at $600k-900k based on conversion paperwork and condition.
• McKinnon G-21E turbine: $900k-1.3M.
• McKinnon G-21G / Antilles Super Goose: $1.2M-2.0M+. Platinum Fighter Sales has listed restored G-21G examples well north of $1.5M.

Major valuation drivers: hull condition (>50% of value on older aircraft), engine time on R-985s, prop time, avionics compliance (ADS-B, IFR GPS), McKinnon/Antilles conversion paperwork, STC documentation, damage history (particularly water-related), and known operator provenance. See Aircraft Valuation Methodology.

The G-21A is subject to decades of legacy ADs; the most consequential recurring items include:

• Wing strut and wing attach fitting inspections — corrosion and fatigue in the wing attach structure are the most critical airworthiness items on any Goose. Repeated AD-driven inspections of the center wing section, spar carry-through, and strut attach points.
• Hull corrosion and bottom skin — recurring inspections of the hull bottom skins, keel, step, bilge, and frame stations. Hull corrosion is the #1 pre-buy killer and the source of the most expensive surprise work.
• Landing gear retraction mechanism and uplock — gear-up water landings and gear-down land landings are the signature Goose accident. Hydraulic and mechanical integrity of the gear system gets close scrutiny.
• R-985 crankshaft, master rod, and cylinder ADs — the Wasp Junior has its own set of ADs tracked by engine serial number; prop governor and magneto ADs also apply.
• Hartzell / Hamilton Standard propeller ADs — blade retention, hub inspection.
• Control cable and pulley inspections — salt water corrosion is an accelerated threat on amphibians.

Common non-AD problems: float strut corrosion, hydraulic leaks in the gear system, fabric control surfaces (some aircraft), mag failures on R-985s, cylinder cracking, exhaust collector ring cracking (a chronic Wasp Junior headache), and interior corrosion hidden behind liners.

Insurance is among the most expensive in general aviation. Typical annual hull + liability for a flying G-21A runs $15,000-25,000 with $1M smooth liability and $500k-800k hull. Turbine conversions carry hull values of $1.5M+ and insurance premiums of $30,000-60,000/year. Key underwriting factors:

• Seaplane/multi-engine seaplane (MES) rating mandatory. Minimum 500 hours total, 100 hours MES, and 25 hours in type typically required; most underwriters want 50+ hours in type.
• Dual-pilot requirement common for the first year for low-time-in-type owners.
• Water operations limitations written into many policies (wave height, approved water bases).
• Hull value caps — very few markets will write hull above $1.5M on a Goose; some syndicates use Lloyd's of London for high-value turbine conversions.
• Salvage value and hull total-loss thresholds are a perennial concern because repair costs on a wooden-era amphibian can rapidly exceed hull value.

See GA Insurance Underwriting for vintage twin and seaplane underwriting category detail.