Piper PA-23

The Piper PA-23, named Apache and later Aztec, is a four-to-six-seat twin-engined light aircraft aimed at the general aviation market that also saw service with the United States Navy and other countries' military forces in small numbers. Originally designed in the 1950s by the Stinson Aircraft Company, the Apache and its more powerful development the Aztec were manufactured from the 1950s to the 1980s by Piper Aircraft in the United States.

Design and development
The PA-23 was the first twin-engine Piper aircraft and was developed from a proposed "Twin Stinson" design, inherited when Piper bought the Stinson Division of the Consolidated Vultee Aircraft Corporation. The prototype PA-23 was a four-seater low-wing all-metal monoplane with a twin tail, powered by two 125 hp Lycoming O-290-D piston engines; it first flew on 2 March 1952. The aircraft performed badly and it was redesigned with a single vertical stabilizer and an all-metal rear fuselage and more powerful 150 hp Lycoming O-320-A engines. Two new prototypes of the re-designed aircraft, now named Apache, were built in 1953 and entered production in 1954; 1,231 were built. In 1958 the Apache 160 was produced by upgrading the engines to 160 hp (119 kW); 816 were built before being superseded in 1962 by the Apache 235. With a 1962 price of $45,000, the Apache 235 was a derivative of the Aztec, fitted with 235 hp (175 kW) versions of the engines used on the Aztec and swept tail surfaces (119 built). In 1958 an upgraded version with 250 hp (186 kW) Lycoming O-540 engines and a swept vertical tail was produced as the PA-23-250 and was named Aztec. These first models came in a five-seat configuration which became available in 1959. In 1961 a longer nosed variant, the Aztec B, entered production. The later models of the Aztec were equipped with IO-540 fuel-injected engines and six-seat capacity, and continued in production until 1982. There were also turbocharged versions of the later models, which were able to fly at higher altitudes.

The United States Navy acquired 20 Aztecs, designating them UO-1, which changed to U-11A when unified designations were adopted in 1962.

In 1974, Piper produced a single experimental PA-41P Pressurized Aztec concept. This concept was short-lived, however, as the aspects of the Aztec that made it so popular for its spacious interior and ability to haul large loads did not lend themselves well to supporting the sealed pressure vessel required for a pressurized aircraft. The project was scrapped, and the one pressurized Aztec produced, N9941P, was donated to Mississippi State University, where it was used for testing purposes. In 2000, N9941P was donated to the Piper Aviation Museum in Lock Haven, Pennsylvania, on the condition that it never be flown again. It now sits there on display.

Variants

 * PA-23 Twin-Stinson
 * Original designation of the Piper PA-23 Apache.


 * PA-23 Apache
 * Initial production version, 2047 built (including the Apache E, G and H).


 * PA-23-150 Apache B
 * 1955 variant with minor changes.


 * PA-23-150 Apache C
 * 1956 variant with minor changes.


 * PA-23-150 Apache D
 * 1957 variant with minor changes.


 * PA-23-160 Apache E
 * PA-23 powered by two 160 hp O-320-B engines.


 * PA-23-160 Apache G
 * PA-23 with longer internal cabin and extra window.


 * PA-23-160 Apache H
 * Apache G with 0-320-B2B engines and minor changes.


 * PA-23-235 Apache 235
 * Apache with 5 seats and 235 hp O-540 engines, 118 built.


 * PA-23-250 Aztec
 * Apache G with modified rear fuselage, new fin and rudder and 250hp Lycoming O-540-A1D engines, 4811 built (including sub-variants)


 * PA-23-250 Aztec B
 * Aztec with longer nose for a baggage compartment; six seats, new instrument panel and changes to systems.


 * PA-23-250 Aztec C
 * Aztec B with either IO-540-C4B5 engines or turbocharged TIO-540-C4B5 as an option, also modified engine nacelles and modified landing gear.


 * PA-23-250 Aztec D
 * Aztec B with revised instrument panel and controls.


 * PA-23-250 Aztec E
 * Aztec D with longer pointed nose and a single piece windshield.


 * PA-23-250 Aztec F
 * Aztec E with improved systems and cambered wingtips and tailplane tip extensions.


 * PA-23T-250 Turbo-Aztec
 * Generally similar to the Aztec F, powered by two TIO-540 piston engines, fitted with a Garret turbocharging system.


 * U-11A
 * United States Navy designation formerly UO-1.


 * UO-1
 * United States Navy designation for PA-23-250 Aztec with additional equipment; 20 delivered, later re-designated U-11A.


 * PA-41P Pressurized Aztec
 * Pressurized Aztec concept, one built.


 * Seguin Geronimo
 * Apache with a series of modifications to the engines, nose and tail.

Military operators

 * Spanish Air Force
 * Escuadrón 912
 * Escuadrilla de Enlace 905
 * Paraguayan Air Force
 * Grupo Aéreo de Transporte Especial/GATE
 * United States Navy
 * Spanish Air Force
 * Escuadrón 912
 * Escuadrilla de Enlace 905
 * Paraguayan Air Force
 * Grupo Aéreo de Transporte Especial/GATE
 * United States Navy
 * Escuadrilla de Enlace 905
 * Paraguayan Air Force
 * Grupo Aéreo de Transporte Especial/GATE
 * United States Navy
 * United States Navy
 * United States Navy

Accidents and incidents

 * On 18 April 1974, Aztec G-AYDE was involved in a ground collision with BAC One-Eleven G-AXMJ at London Luton Airport after the pilot of the Aztec entered the active runway without clearance. He was killed and his passenger was injured. All 91 people on board the One-Eleven successfully evacuated after take-off was aborted.


 * On 29 November 1975, retired F1 driver and Embassy Hill car owner Graham Hill was piloting Piper PA-23-350 Aztec N6645Y from France to London, United Kingdom. His passengers were driver Tony Brise team manager Ray Brimble, designer Andy Smallman and mechanics Terry Richards and Tony Alcock. They were returning from Circuit Paul Ricard, Var, where they had been testing the Hill GH2 car being prepared for the 1976 Formula One season. They were due to land at Elstree Airfield, Hertfordshire, before onward travel to London to attend a party. Shortly before 10pm, the aircraft hit trees beside a golf course at Arkley, Hertfordshire in thick fog. In the ensuing crash and explosion killing everyone on board.


 * On 15 April 1978, Hollywood stunt flyer Frank Tallman was ferrying a Piper Aztec from Santa Monica Airport, California, to Phoenix, Arizona under visual flight rules when he continued the flight into deteriorating weather, a lowering ceiling and rain. He struck the side of Santiago Peak in the Santa Ana Mountains near Trabuco Canyon at cruise altitude, dying in the ensuing crash.