The Twin Navion: A Rare Restoration Story

Occasionally, I get lucky and an article falls into my lap. That is exactly what happened last September when I received a Facebook message from Mack McMillan, asking if I would be interested in writing an article about his TEMCO-Riley D-16A, better known as a Twin Navion. Yep, I was interested, all right! We stayed connected and finally had a chance to meet at Sun ’n Fun.

To understand the concept behind the Twin Navion, let’s look at the history of the original Navion. North American Aviation established itself as a premier airplane manufacturer during WW-II, producing the highly successful B-25 Mitchell bomber and, of course, the P-51 Mustang. As a direct result of the war, aviation experienced quantum leaps forward in technology, airport facilities, and overall acceptance by the civilian sector. Thanks to military training and the G.I. Bill, tens of thousands of pilots were created, creating a demand for general aviation aircraft. North American Aviation envisioned an aircraft that would perfectly match the expected postwar boom in civilian aviation, and the Navion was designed along the general lines of the P-51 Mustang. North American built 1,109 Navions between 1946 and 1947, which included 83 L-17As for the U.S. Army and National Guard.

In the summer of 1947, Ryan Aeronautical Company acquired the design, ultimately building 1,240 Navions (powered by 205-hp Continental O-470 engines or 250-hp Lycoming O-435 engines), including 163 aircraft for the U.S. armed forces, before production ended in 1951. In June 1960, the TUSCO corporation set up the Navion Aircraft Company to build a revised version, the Navion Rangemaster G. Production of the Navion ended in 1974.

So how did the Twin Navion come to be? In 1951, Charles “Chuck” Daubenberger ran a manufacturing company called Dauby Equipment Co. Inc., with his brother. During WW-II, its business produced fasteners, clamps, and cables for the aviation industry. Following the war, Daubenberger earned his pilot’s certificate and began purchasing a succession of airplanes. The company owned a single-engine Navion, which he often flew to Montana. He was unhappy with how the six-cylinder Continental engine would run while flying over the mountains, so he approached the Acme Aircraft Company in Lomita, California, in search of a solution.

Acme Aircraft’s owner was Roger Keeney, formerly with Douglas Aircraft Corp. Formed in 1936, Acme Aircraft was an FBO, and the company also converted Boeing Stearmans into crop dusters and performed piecemeal maintenance work. Daubenberger asked Keeney about a solution to his problem and, at first, Keeney suggested several existing twin-engine aircraft, mostly retired transports like the Beech C-45 and Douglas C-47, which were too large and too expensive for Daubenberger. At the time, there were no commercially available light twin aircraft, so Keeney suggested putting two engines on the Navion that Daubenberger was already flying.

Keeney chose Jack Riley Sr. to lead a team of engineers to obtain approval for his project through a Major Modification or Repair form, commonly called the 337 form. Work began on the conversion in 1951. The team’s immediate challenge was to find the proper engine for the twin, and nothing new and suitable existed. Keeney sent out requests to the major engine manufacturers, and Lycoming was the first to respond. In order to quickly deliver an engine, the manufacturer decided to work with an existing design. They selected a four-cylinder, 125-hp O-290-D and the engine mounts, accessories, and cowlings from the Piper PA-18 Super Cub. Keeney had his engine.

In an effort to keep the conversion as simple as possible, Riley chose to leave the cabin aft of the firewall alone. The engine compartment was left empty, enclosed by a sheet metal dome. The vertical stabilizer was replaced with a modified horizontal stabilizer from another Navion. The landing gear remained original equipment. Most of the conversion, of course, occurred between the cabin and the wingtips. As testing progressed, Keeney found solutions to many of his problems in the form of parts harvested from existing aircraft. On Nov. 10, 1952, the CAA awarded the Twin Navion its certification. The experimental X-16 became the D-16.

In 1952, Jack Riley formed Riley Aircraft Corporation and purchased the production rights to the Twin Navion conversion. He converted a second aircraft, specifying 140-hp engines, and ended up putting the Riley D-16 Twin Navion into production utilizing the 150-hp Lycoming O-320 engines. He subsequently converted 19 aircraft before subcontracting production to Temco Aircraft. Temco then purchased the sole production rights and produced a further 46 conversions under the name Temco D-16. The design was upgraded in 1954 to include 170-hp Lycoming O-340 engines plus increased fuel capacity in wingtip tanks. The upgraded model was officially named Temco D-16A but typically marketed as the Riley 55 for the 1955 model year. Forty-five were built. Many of the earlier D-16 models were later upgraded to D-16A standards.

Meanwhile, a parallel project was undertaken by White Engineering in San Antonio, Texas. This conversion featured a pair of Continental O-470-3 air-cooled flat-six engines, rated at 240 hp each. The Navion’s engine compartment was converted to a baggage compartment, a new tail fin made of fiberglass was installed, and tip tanks made from recycled WW-II napalm canisters were added. This conversion was originally designated the WE-1. Soon after its first flight in 1953, the rights were sold to Camair and Civil Aviation Authority type certification was awarded in May 1955 under the name Camair 480. Camair built only 25 examples before selling off the rights in 1959. The ownership of these rights would change hands twice again over the following decade, but only another eight aircraft were built.

By this time, larger airplane manufacturers were starting to address the need for a light twin general aviation aircraft. 1954 saw both the Piper PA-23 and Cessna 310 enter production. The price points of these new aircraft were considerably lower than the cost of converting used Navions, and, after several iterations, the Twin Navion project finally died on the vine. Piper eventually built nearly 7,000 PA-23s and over 6,000 Cessna 310/320s were built.

There is an ongoing debate regarding the “correct” pronunciation of the aircraft name. Here is the best that I have been able to come up with. North American built 1,109 Navions in 1946–1947, and it was originally spelled NAvion and pronounced “NAVY-on,” the “NA” standing for North American. In 1949, the production was restarted by Ryan, and the aircraft was renamed “Navion.” I welcome any additional clarification.

Joseph “Mack” McMillan is the current owner of one of two known airworthy TEMCO-Riley D-16A Twin Navions in the United States. Registered N119N, serial number TTN-51, this airframe began life as MSN NAV-4-425, registered NC91680. Not much is known about the aircraft prior to conversion, so Mack would welcome any information about NAV-4-425. In 1954, the airframe was bought by Jack Riley, converted to D-16A standards (A.K.A. Riley 55), redesignated TTN-51, and reregistered N119N. The aircraft was certified in May 1955 and delivered to Tupman Motors of Los Angeles. Tupman owned the airplane until September 1956, when a new Cessna 310 replaced it. Since then, N119N has changed hands a few dozen times and has survived several mishaps. According to twinnavion.com, the aircraft suffered two nosewheel failures at Imperial County Airport, California, between 1956 and 1958, and failure of the right-hand propeller while in flight in 1959. On Dec. 1, 2006, N119N suffered a nosewheel collapse while taking off from Point Roberts Airpark, Washington. The pilot and sole occupant survived without injury, but its nacelles were ripped wide open. It took two years to repair, but it was flying again in the summer of 2008.

Enter Mack McMillan, age 46, and mechanic extraordinaire. After working for three different airlines, he opened his own aircraft repair business to include overhaul and restoration services. He does not have a private pilot certificate due to a medical condition, but he has amassed considerable stick time as an SIC. By this time, he was part of the Geico Skytyper Team as a mechanic and IA. Mack says, “My best friend, Tommy Spano, had developed a nice little business model of finding airplanes that need a little TLC and buying them on the cheap. I would do the rehab work, and then we would sell the refurbished aircraft and split the profit, after all the bills were paid. Sadly, he was killed in a motorcycle accident in 2022, leaving his father with several of his projects, including the Twin Navion. The airplane immediately piqued my interest because, well, it was definitely an unusual type.”

Little in aviation is easy, and this project was no exception. First, Mack had to lay eyes on the aircraft, which was sitting on a basically abandoned airfield in Boardman, Oregon. He found that the field was literally a portable T-hangar that was staked to the ground and a runway that was overgrown. No fuel, no electricity, no FBO, no sign of life, not even a real road to access the aircraft where it was located. He needed bolt cutters to get into the hangar, but after giving it a thorough assessment, Mack determined that it was salvageable, despite years of neglect.

In February 2023, Mack drove back out to Boardman with a trailer, ready to work. Everything had to be trucked in, and work was done in a winter environment. Tire replacement, oil and filters replacement, and even trucking in some 80 gallons of gas. McMillan recalls, “We spent four or five days out there working on the airplane going through the gear swing and going through compression checks. We borescoped the engines, pulled the jugs, cleaned the fuel systems, went through the mags, checked the wing ribs, spars, checked all the fluid lines, and cleaned, cleaned, and CLEANED. Finally, I secured the bird and headed home to start addressing the paperwork challenges.”

Over the summer, Mack had to assemble manuals and build flight supplements. He had already obtained documentation and more maintenance manuals, which he found from the Navion Society and also from the Pima Air and Space Museum in Arizona. Mack also credits Troy Welsh, who owns the other flyable Twin Navion, located in Texas, with providing a lot of maintenance information. He notes that there is a third Twin Navion on the U.S. Register, but it is not currently airworthy.

The third Twin Navion on the U.S. Register belongs to Robert Fratti, 56, of Nampa, Idaho. Fratti is now a 747 captain for Atlas Air, based in Anchorage. He has owned several general aviation aircraft over the years, including N107N, a Riley D-16, TTN-4. He tells his story. “I was a first officer for Atlas, and I had a long layover in Japan one trip. I had bid on a Twin Navion in Pennsylvania. I was drinking beer in Japan when my phone goes ‘Ding.’ I’m like, oh crap, I want it. I did not think I’d come close. But I ended up having to sell it because it had been pushed out in the weeds and the animals had gotten into it. Nevertheless, I kept looking for one. I like airplanes that were built by somebody’s hands.” His search eventually led him to N107N. This aircraft will be flyable again with a bit more TLC. “I also own airframes for another D-16 and a pair of D-16As. Eventually, I hope to restore at least a couple of them to airworthy condition and sell them.”

Meanwhile, in September 2023, McMillan returned to Boardman and moved the Twin Navion to Pasco, Washington, around Aug. 14, 2023. There, he had proper airport facilities, which made it easier to work on the aircraft. He worked on it for a couple of days, dealing with some generator issues. Winter forced Mack to keep N119N in Pasco until spring of 2024. By then, he had selected David Singer as the primary pilot of the Twin Navion. Singer, now 28, came to Mack to help with a repair job on a Mooney, which he was a partner in. Following a second mishap with the Mooney (he was not involved with either incident), Singer decided to get out of that partnership and invest in his own aircraft. Mack explains, “I found him another Mooney, which he has now. We developed a friendship, and he brought his airplane to me next year for annual. At that time, he had asked if I needed anybody to work for me, which I did not, at that time. I told him that I was looking for a ferry pilot and so we became buddies, and I ended up mentoring him. And, eventually, he ended up coming to work for me. He did not have an A&P, but he knew how to turn a wrench, taking panels off and doing busy work for about 2.5 years. Once I finally had the twin ready, he was like, hey, can I fly? He already had private pilot qualifications, but I explained that he needed his multi-engine rating, so he went and got his multi.”

In the spring of 2024, Mack and David went back out to Washington with another friend, a customer named Hernan Aries, who was looking to buy an A36 Bonanza. He continues, “The Bonanza happened to be in Spokane, and it just so happened to be the same weekend that I was going out to work on the Navion. Subsequently, I did a prebuy on the Bonanza, and he ended up buying the aircraft, and then we took the aircraft and flew down to the Navion in Pasco. We worked on it for another couple of days, making sure that everything was right in it.”

On Aug. 6, 2024, Mack did another test flight upon completion of another annual, and on Aug. 8, 2024, Mack and David headed back east in the twin as a two-ship, accompanied by the A36. He recalls, “It took us three days, and we flew as a two-ship, so if anything happened, we had a chase ship with tools, and if we had to abandon the airplane somewhere because something happened, we had a ride home. Our flight was uneventful, and we brought the Navion to its new home at Claremont Airport (58M) in Elkton, Maryland. Once the airplane was home, we worked closely with Troy Welch’s mechanic. We put the airplane up on jacks, pulled the gear out of it, cleaned everything, rebuilt everything, and re-rigged everything. We even figured out a way to plug a hydraulic mule into the aircraft so that we could run the gear up without having to pump it up and down. Once we were satisfied that everything was in good working order, we spent several months flying short hops to put time on the engines and give the plane some ‘exercise’ after it had been sitting for years.”

The “Big Reveal” of Mack McMillan’s Twin Navion occurred in June of last year, when he brought the plane to the Reading Air Show as a static display. He fondly remembers, “There we were, parked on the warbird ramp with a bunch of other WW-II aircraft on both static and flying display. It certainly generated a lot of interest! Then in August 2025, we took it to an airshow at one of the little local airports near where I live, N57 New Garden Airport. Interestingly, I met several other Twin Navion people who knew people who had them or knew where some were parked. I actually met one father and son from Oklahoma who have one, and so I have been collaborating with them to try and help them get theirs put back together.”

Since then, Mack and David have been working to maintain and improve the twin. Mack notes, “We must be very thorough with the inspections. We have made an extensive punch list, and we continue working on items to improve the airplane. Just before Sun ’n Fun, we put in a new ADS-B transponder, and we will continue working on the airplane and making it as nice as I can, you know, while flying around and displaying it at airshows. I intend on adding a GNC 355/GI 106, PS Engineering 8000B audio panel and CGR twin 30 engine monitors to the aircraft in May. We were selected to fly in the showcase at Sun ’n Fun, which gave us a great deal of visibility.” It was fun to have the aircraft at Sun ’n Fun as it also drew a lot of attention and piqued a lot of interest among the Navion community and many other aviation enthusiasts. We were approached by several other people, including the original owner of the first Twin Navion currently in Kentucky in unairworthy condition, about potentially helping him get it going again. With that and, hopefully through this article, Mack McMillan and his rare Twin Navion will appear on the airshow circuit for years to come.