The Ryan Navion D-16A belonging to Mac McMillan represents one of the rarest airworthy twins in the United States, with only two of its type reportedly remaining in flying condition out of a total production run of just 90 twin-conversion Navions ever built. The aircraft did not begin its life as a twin — it originated as a single-engine military L-17 Navion before undergoing a factory-style conversion engineered by Jack Riley and collaborators. The conversion involved grafting in twin engine nacelles sourced from a Piper Apache, reinforcing the wing spar, and enlarging the rudder to provide adequate yaw authority in asymmetric thrust conditions. The motivation for the twin conversion was fundamentally operational: the standard Navion airframe powered by a Continental E-225 struggled with density altitude performance in western mountain environments when loaded with passengers and full fuel, a limitation the twin configuration addressed by distributing power across two Lycoming O-340s — an engine that was purpose-developed for this specific application as an enlarged variant of the O-320 and which sees almost no other significant use in the certificated fleet.
From a systems standpoint, the aircraft presents an unusual profile that blends pre-jet-era engineering with modern regulatory compliance additions. Its five-tank fuel system holds 144 gallons total, yielding an endurance Singer estimates at nearly five hours — a meaningful range capability for a piston twin of this vintage. The landing gear is fully hydraulic with a relatively simple emergency extension mechanism, consistent with Navion-era design philosophy. Among the more striking anachronisms is a four-probe EGT system salvaged from a B-24 Liberator, with two probes per engine — a component Singer acknowledges is effectively unobtainable through normal supply channels and which is being replaced as part of a planned instrumentation upgrade. That upgrade will introduce a Garmin GPS 355 and Gulf Coast Avionics engine monitors, eliminating six analog gauges from the right-side panel while bringing the aircraft into better alignment with modern IFR and monitoring practices. Current communication and navigation equipment consists of a Bendix/King KX 155 nav/comm and a II Morrow GNC 250 GPS, with ADS-B out already installed via a Pariot transponder.
The aircraft's handling characteristics are notable given its configuration. Singer describes the D-16A as lighter in feel than a Beechcraft Baron despite the twin-engine layout, with forgiving slow-flight behavior and benign landing characteristics — qualities consistent with the Navion family's reputation for docility. This is operationally relevant context for pilots who might assume the twin conversion imposed heavier or more demanding control forces. The airplane reportedly accepts four occupants with 80 percent fuel without performance degradation, which validates the original design rationale for the conversion and distinguishes it meaningfully from its single-engine predecessor. The comparison to a pickup truck in handling feel, while colloquial, signals a predictability and linearity that experienced twin pilots would recognize as a hallmark of well-sorted, low-wing piston designs with moderate wing loading.
The broader significance of the McMillan Navion lies in what it illustrates about the fragility of low-volume certificated type populations. With 90 total twin Navion conversions produced and only two D-16A variants known to be flying, the aircraft represents a category of American general aviation heritage that sits at acute risk of permanent loss. Many of the surviving airframes, Singer notes, have deteriorated beyond economic recovery. The five-year restoration effort required to return this example to airworthy status — including multiple transcontinental trips to retrieve parts and tooling, work conducted at a remote field with minimal infrastructure, and continuous systems refinement post-delivery — underscores how intensive the stewardship of rare certificated types can be. For operators and mechanics working outside the mainstream piston fleet, this case illustrates both the feasibility and the resource intensity of preserving low-production-run aircraft that carry no manufacturer support infrastructure.
For the broader professional aviation community, the Twin Navion story touches on several persistent themes: the role of supplemental type certificate conversions in expanding the operational envelope of legacy designs, the increasing difficulty of sourcing parts for pre-1970s airframes as original components deteriorate or disappear from the supply chain, and the tension between historical authenticity and the practical need for modern avionics compliance. The planned shift to a Garmin GPS 355 and digital engine monitoring reflects the same pressure felt across the vintage piston fleet — owners must modernize instrumentation to remain viable for cross-country and IFR operations even when doing so means replacing irreplaceable original equipment. Singer's aspiration to acquire an ownership stake and preserve the aircraft for decades signals the kind of long-term custodial commitment that increasingly defines the survival of these narrow-production-run types.