Grumman G-73 Mallard

The Grumman G-73 Mallard is a twin-radial amphibious flying boat designed by Grumman at Bethpage, New York as a step up from the pre-war grumman-g21-goose and grumman-g44-widgeon. First flown on April 30, 1946, the Mallard was Grumman's attempt to build a post-war, all-metal, 10-passenger amphibian for feeder-liner and executive use. Only 59 airframes were built between 1946 and 1951 before Grumman ended production to focus on jet-era military work.

The Mallard became an icon of Caribbean and South Pacific operations. King Farouk of Egypt owned one as a Royal Flight aircraft; Chalk's Ocean Airways flew them on Miami-Bimini-Nassau routes for decades; Paspaley Pearling/Pearl Aviation operated (and still operates) Mallards in Australia's pearl-farm network. It is a tailwheel-derived hull design with tricycle retractable gear, a high cantilever wing carrying two 600 hp Pratt & Whitney R-1340 Wasp radials, and wingtip floats. Roughly 30 airframes remain on the FAA registry as of the mid-2020s, with a worldwide flying fleet in the high-teens to low-twenties. It is firmly a collector/owner-operator and specialty-commercial airplane, not a general-GA platform.

The Frakes Aviation turbine conversion (Cleburne, TX) is the dominant in-service configuration. The STC raised max gross to 14,000 lb, added better props, and modernized nacelles. Piston-powered originals are now rare flyers; most remaining active aircraft are G-73T turbines.

Piston G-73 book numbers are sea-level, standard-day, max-gross: 187 kt max, 160 kt cruise at 8,000 ft, 1,290 fpm climb, 23,000 ft service ceiling, 1,200 nm range at long-range cruise with ~810 lb payload. Real-world block speeds are 140-150 kt because operators rarely push the R-1340s to book power — fuel burn and cylinder temps climb fast above 60% power.

Turbo Mallard (G-73T) transforms the airplane. The PT6A-34s add ~300 shp total over the radials, drop useful load penalty (turbines are lighter than R-1340s plus their oil tanks), and raise MTOW to 14,000 lb. Max cruise ~191 kt, long-range cruise ~170 kt, service ceiling 24,500 ft, initial climb ~1,350 fpm, range ~1,400 nm. The turbine also solves the biggest piston problem: hot-start reliability at remote salt-water bases and TBO (3,600 hr on -34 vs 1,200 hr on the R-1340).

Water takeoff on the hull adds ~20-30% to the land ground-roll figures above, and is highly sensitive to sea state. The Mallard handles 2-3 ft chop competently; beyond 3 ft, prudent operators stay on wheels. Single-engine performance is marginal at max gross in either variant — positive SE climb exists, but climb gradients are below what modern turbine twins deliver.

With 380 gal usable (2,280 lb of 100LL), the piston G-73 is a full-fuel + full-cabin airplane by design — useful load is 3,400 lb, so subtracting fuel leaves 1,120 lb for crew, pax, and bags. That is only 5-6 people at FAA standard weights on a full-fuel mission.

Practical mission mixes:

• Full fuel, 2 pilots + 6 pax (1,360 lb): Slight overload; burn 200 lb on taxi/climb and departure is legal. 1,200 nm range, ~7.5 hr endurance.
• 2 pilots + 10 pax (2,040 lb): Requires reducing fuel to ~220 gal (1,320 lb), yielding ~650-700 nm range. This matches the Chalk's Miami-Nassau and Paspaley inter-pearl-farm missions.
• Freight config, 2 pilots + 3,000 lb cargo: Requires reducing fuel to ~70 gal (420 lb) — roughly 200 nm range. A short-hop utility load.

The Turbo Mallard (G-73T) significantly improves the envelope: MTOW 14,000 lb adds 1,250 lb of useful load over the piston airframe (partially offset by heavier-empty turbine installation), and jet-A is denser. Net effect: at 10 pax and full fuel, the G-73T flies ~900 nm vs ~650 nm for the piston. This alone is why every high-utilization commercial Mallard operator converted to turbines by the 1980s.

• Business travel (4): Historically the Mallard's core role — 10 pax in a pressurized-feeling cabin to anywhere with a runway, lake, or protected bay. The G-73T version still serves this mission beautifully in a handful of corporate and island-resort operations. Modern alternatives (King Air, PC-12) are faster, cheaper to run, and easier to insure, which cap the business score. See business-travel.
• Cross country (6): 1,200-1,400 nm range and 160-191 kt cruise make it a credible long-leg airplane, especially over water where the amphibian capability adds bail-out options. See cross-country.
• Backcountry / utility water ops (5): Superb water manners, excellent hull, huge cabin, but the 66 ft wingspan and 12,750+ lb MTOW rule out tight rivers and small lakes; it's a big-water airplane.
• Cargo hauling (5): 3,400 lb useful load with good cabin volume and double clamshell doors; used in Australia for pearl-farm support.
• Training, aerobatics, local fun: Not applicable. Vintage radial amphibian twin insurance and operating cost rule these out.
• Surveying (3): Cabin volume is good but per-hour cost is roughly 5-10x a Cessna 206 or Partenavia.

Factory panels were 1940s-50s round-gauge with basic low-frequency nav and ADF. Almost every flying Mallard has had at least one major panel refresh. Typical modern configurations:

• Baseline refurb (~$40-80k): Garmin GTN 650/750 + GTX 345 ADS-B In/Out + GI 275 attitude/HSI + dual 8.33 kHz comms. Retains steam backup.
• Mid-tier ($120-200k): Dual GTN 750Xi, dual G5 or G500 TXi flight display, GFC 600 autopilot STC (limited Mallard approvals — often custom field approval), Garmin GWX radar.
• Turbine G-73T full glass ($300-500k+): G600/G500 TXi PFD/MFD, synthetic vision, dual nav/comm, radar, TAWS, dual ADAHRS. Common on corporate Mallards.

Autopilot STCs are the limiting factor — the Mallard is not on the mainstream GFC 600 AML and typically requires custom field approvals.

• Frakes Turbine Conversion (STC SA2323WE) — The single most valuable STC on the airframe. Replaces R-1340s with PT6A-27 or PT6A-34, new cowlings, fuel system, props (Hartzell four-blade reversing). Conversion cost historically $1.2-1.8M; remaining installations trade in the $2M+ market.
• Frakes Gross Weight Increase — Raises MTOW from 12,750 to 14,000 lb on turbine-converted airframes.
• Extended-Range Fuel Tanks — Wing bladder additions to ~480 gal, pushing range past 1,500 nm.
• Four-bladed Hartzell props (piston) — Reduces tip noise and improves climb on R-1340 airframes.
• Weather Radar nose installation — Several field approvals for Garmin/Honeywell radar in modified nose.
• Cargo door enlargement / medevac interiors — Several one-off STCs used by Pacific operators.

See maintenance-ecosystem.

• Parts availability: poor. Grumman stopped supporting the type decades ago. Most airframe parts are sourced from a small community of type specialists (Dean Franklin in Miami, Frakes Aviation legacy in Texas, Victoria Air Maintenance in BC) or fabricated under owner-produced-parts rules.
• Mechanic familiarity: rare. Fewer than two dozen A&P/IAs worldwide have significant Mallard time. Annual inspections typically require ferrying the airplane to a specialty shop.
• Annual inspection cost: $40,000-80,000 base, $150,000+ if any spar or hull work is discovered.
• Annual operating budget (all-in, ~150 hr/yr): Piston G-73: $175,000-250,000. G-73T Turbine: $275,000-400,000+ (higher fuel burn, higher insurance, turbine reserve).
• Expensive items: R-1340 overhauls ($85k/side), hull re-skin ($100-200k), gear actuator rebuilds ($15-30k each), prop overhaul ($12-20k each).
• Ferry logistics: Moving a Mallard to a shop is non-trivial — pilots with fresh type experience are rare and commanding.

Mallard values split sharply by engine and documentation. See valuation-methodology for methodology.

• Piston G-73 (R-1340), project or tired: $400k-900k. Typically a restoration candidate with expired engines or open spar inspection work.
• Piston G-73, well-maintained flyer with documented post-AD spar inspection: $900k-1.4M.
• Piston G-73, museum-quality ground-up restoration (e.g., Victoria Air Maintenance rebuilds): $1.5-2.0M.
• Frakes G-73T Turbo Mallard: $2.0-3.5M+ depending on engine times, avionics, and interior.

The primary value driver is post-2006 AD compliance documentation. An airframe with unpeeled sealant and undocumented doubler history is essentially uninsurable and unsellable as a flyer. Conversely, a freshly complied, corrosion-free wing adds $300-500k of value.

Engine time remaining matters enormously on piston airframes (Wasp overhauls dominate the cost model); on turbine airframes, hot-section and TBO status of the PT6A-34s drive price the same way any King Air would.

AD 2006-02-07 (wing spar / structural inspection) is the defining AD for the fleet. Issued as Emergency AD 2006-01-51 on December 30, 2005 — eleven days after the Chalk's Ocean Airways Flight 101 in-flight wing separation on December 19, 2005 — the AD mandates detailed visual inspection of the wing from WS 77L to WS 77R, front spar to rear main spar, removal of all prior repair doublers to permit inspection of underlying structure, and stripping of fuel-tank sealant in the wet bays to inspect skins, stringers, and both spar caps. The Chalk's accident was caused by fatigue cracking in a z-stringer at the wing root that had been repeatedly patched over with doublers and hidden by tank sealant. The NTSB faulted Chalk's maintenance program and the FAA's oversight; fatigue cracking was subsequently found on the opposite wing of the accident airplane and on several other fleet airframes.

The post-accident inspection program grounded most of the fleet for extended periods and forced many owners into expensive wing rework or retirement. Remaining Chalk's airframes were ultimately scrapped or sold after the airline ceased operations in 2007.

Other recurring problems:

• Hull corrosion — Salt-water operations rot lower hull skins and bilge stringers; a full re-skin is routine mid-life work.
• Wing-root and spar cap corrosion — Directly connected to the AD above; any repair history must be fully documented.
• R-1340 cylinder cracks and valve issues — Wasp overhauls are $80-120k per engine and turnaround can be 9-18 months.
• Main gear retraction actuators and uplocks — 70-year-old hydraulic components; rebuilds are shop-specific.
• Float / wingtip float attach fittings — Cycle-limited and inspected at every annual.
• Fuel bladder aging — Rubber bladders in the wet bays harden and leak; replacement cycle 15-20 years.

Insurance is the hardest single topic for a Mallard owner. See insurance-underwriting.

• Hull premiums: $25,000-50,000+/year on a $1.7M hull, with $50k+ deductibles and no in-motion water coverage below a named-pilot standard.
• Liability: $1M smooth is difficult; most owners carry $1M/$100k pax with special underwriting.
• Pilot requirements: Typically ATP or Commercial with 1,000+ multi, 500+ seaplane, 100+ in type, and annual recurrent at a specialty school (e.g., SimCom / type-specific). First-year coverage for a low-time-in-type pilot is routinely refused.
• Underwriting quirks: Age of airframe, history of corrosion repairs, and the post-Chalk's spar AD compliance dossier are the three biggest factors. Underwriters still treat the Mallard as a special-scrutiny risk because of Flight 101.

A small handful of carriers (Starr, Global Aerospace, one or two Lloyd's syndicates) write the type at all; many brokers decline on first call.