In 1957, a "Strato Courier" set an altitude record over Mexico City, Mexico at 31,200 ft powered by a geared Lycoming GSO-480-A1A5 (340 hp), only one was built. The Super Courier, a more powerful derivative, was used by the U.S. Air Force from 1958 onward, by the U.S. Army Special Forces in the 1960s and 1970s and by Air America during the Vietnam War as the U-10. In U.S. Army and Air Force service, the U-10 Super Courier was used for liaison work, light cargo and supply drops, psychological warfare, forward air control (Air Force), insertion and extraction by land and sea (Army), and reconnaissance. Various versions were produced up through the 1980s, including turbine-powered variants. The Super Courier saw military service in the United States as the U-10 (ex L-28). Over 120 were built: The L-28A (2, later redesignated U-10A), U-10A (26), U-10B extended range and paratrooper doors (57), and the U-10D with a higher gross weight(36). There was no U-10C. Helios remain very popular among bush pilots in Canada (32 current) and Alaska and missionaries who fly into rough, relatively unprepared jungle airstrips because of its superior STOL abilities. Some operators use the Helio Couriers for aerial observation. Both Winged Vision Inc. of Gaithersburg, Maryland and the Pima County, Arizona, Sheriff's Department each operate two of the rare tri-gear model and mount gyro-stabilized cameras under the wing for aerial observation. Pima County mounts a FLIR camera for law enforcement, and Winged Vision mounts a high definition television camera for coverage of major sports events. Variants Koppen-Bollinger Helioplane Original prototype soon re-named Helio Courier. Helioplane Four unknown possible variant. Helioplane Two unknown possible variant. Hi-Vision Courier unknown possible variant. H-291 Prototype, one built. Variant with a Lycoming GO-480-G1D6, purchased by USAF as U-10D, 173 built. HT-295 Super Courier or Trigear CourierH-295 with tricycle undercarriage, 19 built. H-250 Courier H-295 with lengthened fuselage and Lycoming O-540-A1A5 engine, 41 built. H-391 Courier Prototype with Lycoming GO-435-C2 engine, one built. H-391B Courier Production version of H-391, 102 built. H-392 Strato Courier High-altitude version of H-391 with Lycoming GSO-480-A1A5 engine (340 hp). H-395 Super Courier H-391B with Lycoming GO-480-G1D6, purchased by USAF as U-10A and U-10B', 138 built. H-395A Courier Variant of the H-395 with a Lycoming GO-435-C2B6 engine, seven built. H-500 Twin Courier Twin-engined H-395 for the CIA. Very little information available except seven delivered to the CIA under front designation U-5.