The development of the Twin Navion is a complicated subject. Most of the people involved with its development have passed, leaving little in the way of written anecdotes or memoirs. Twin Navions weren't glamorous, so they escaped notice from many trade publications, leaving its history to be passed by means of the faded memories of its participants.

According to one source, Ryan's Jake Miller spent a great deal of effort trying to convince Claude Ryan, President of Ryan Aeronautical to produce a twin engine variant of the Navion. Ryan's obsession however was with military aircraft and he gave little interest to the Navion, or to continued development. Instead Miller was lured away to Piper where he helped the struggling company introduce its own light twin - the Apache.

Wishful thinking on the part of Ryan's employees aside, the real story of how the Twin Navion came about starts in California. C.J. Daubenberger, Roger Keeney, and a team of engineers and draftsmen from California. It took seven months for the group to design, manufacture and install 1,837 new parts via more than 2,000 engineering drawings.

John Martin performed the plane's first test flights, and on November 10, 1952, one full year after starting, with their Twin Navion, the plane, designated D-16 (D for Daubenberger) received its CAA certification. Interestingly, before the Twin Navion the Civil Aviation Authority had no way of certifying modifications as extensive as those done for Daubenberger (all were approved using the Major Repair and Alteration Form). This, plus a couple of other major conversions led the CAA to develop the Supplemental Type Certification process that is still in place today.

Almost immediately word of the D-16's existence spread across the United States, and in Florida, Jack Riley entered the Twin Navion story.

Jack Riley was a self-made millionaire in the oil business and a natural salesman. He'd broken records selling de Havilland's Dove business plane, and before Ryan ceased production, was recognized as the top Navion salesman for the Southeastern USA. Riley was now a man looking for a new challenge. After only a couple days in California, the businessman returned home with the Twin Navion's production rights.

Acme Aircraft was contracted to modify a second Navion into D-16 configuration for Riley. This plane arrived in October 1952 and featured a much blunter nose cone, 140hp engines and a newly upholstered cabin. It took more than 1,700 man-hours to complete.

Riley Aircraft Corporation meanwhile had been growing into an aircraft manufacturer. During the summer of 1952, Fort Lauderdale's Granere Aviation was purchased for its hangar facility. The 12,000 square-foot building was to become the new factory.

Eager to sell his new twin Jack Riley took his plane to Dallas, Texas, where he demonstrated it to some 30 or 40 potential customers. Riley admitted that owners of single Navions were his primary customers, since they already knew the plane and could continue to expect the same performance, handling and ruggedness that they'd come to expect from their own planes. That tour resulted in the company's first sale, with two more following. Within a couple months the books were filled with orders for more than three dozen planes.

The first major change to production occurred in November of 1952 when the controllable Sensenich Skyblade propellers were replaced with Aeromatic units. These too were soon replaced at the beginning of December 1952 when Hartzell finished certifying its new fully-feathering, constant speed propellers. A major lack of performance caused Riley to purchase Daubenberger's prototype, which he in turn used to prototype the installation of new 150hp Lycoming O-320 engines. This change also meant the use of custom-built cowlings in place of the 'borrowed' Piper units.

As production began, prices increased from $20,000 (initial sale price) to $24,850. This was nearly three times the price of a used single Navion but with Jack Riley's salesmanship there were always customers. In March 1953 a production agreement was entered with TEMCO Aircraft Corp., a well known subcontractor, maintenance provider for the USAF and small plane manufacturer. The next month, TEMCO purchased the exclusive production rights to the 'Riley Twins.' Jack Riley meanwhile returned to Florida where he remained responsible for marketing and sales. It also appears that Riley Aircraft served as a broker for Navions, buying them on the used market and then reselling them to TEMCO when an airframe was needed.

On September 1, 1954, TEMCO introduced a more powerful variation of the 'Riley Twin' called the D-16A, and marketed as the 'Riley 55.' The power increased to 170hp through the use of brand-new Lycoming O-340-A1As. Although the top and cruise speeds remained the same at 190 and 153 mph, gross weight for the D-16A increased to a very respectable 3,600 lbs (850 lbs above a stock Navion A and 250 lbs more than a D-16). Tip tanks were introduced, increasing the capacity to 144 US-gallons and stretching the range from 720 to 1,200 miles. A standard paint scheme was also introduced. The first production aircraft flew on February 23, 1955.

By the time the last twin Navion rolled out of the TEMCO factory the light twin market had been flooded with new planes; Piper had taken a Stinson design and expanded it into their PA-23-150 Apache, Cessna had their large 310, and Beech had the Model 95 Travel A. In the pricing market Piper was the immediate winner. A new Apache sold for the same price as the 'Riley 55' conversion and a single Navion wasn't required as a starting point. All told, when production of the 'Riley 55' ended in September 1957 a total of 107 D-16s and D-16As had been converted. Some D-16s would later return to the TEMCO factory to be upgraded to D-16A standards.

After the production line closed, the type certificate was sold to Universal Aircraft Industries of Denver, Colorado, part of the American Navion Society. Under their operation both Twin Navions continue to be supported and cared for.