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Jet Engine Testing

Time Flies: GE’s Original Flying Testbed Jets Off Into History

Brendan Coffey
November 28, 2018

The history of GE and modern aviation are closely linked. Few symbols embody the connection more than the original GE flying testbed, a 49-year-old Boeing 747-100 that served as an airborne lab for engineers testing generations of new jet engines. The plane, the last operating model of the first variant of the iconic 747 jet, made its final flight earlier this month.

“This is my absolute favorite to fly, even more than other 747s,” says Gary Possert, who has been flying GE testbeds for more than two decades and guided the plane on its final 358-mile run from Victorville, California, to its new home at the Pima Air & Space Museum in Tucson, Arizona. “It had some physical characteristics that made it very preferable to handle,” he says, from its larger tail size to its cable-based mechanical systems.

The 747-100 GE jet engine testbed was a crucial part of the process that vetted and certified 11 engine models and 39 different engine builds, including the GE90, the world’s most powerful jet engine, and GEnx engines for the Dreamliner and the latest variant of the 747. “We found the airplane was very adaptable to any engine that we came up with at GE, big and small,” Possert says.

The long life of the 747-100 is impressive in itself. Remarkable, too, the testbed was also the last operating 747-100 — which means the plane stretches back to an era when passengers still got dressed up to fly and carriers still experimented with interior layouts for reasons other than maximizing passenger numbers.

The 747-100 was the first model of that jet built by the Boeing Company, which produced 169 of the first edition. The testbed rolled off the assembly line in 1969, the 16th constructed, and was operated by Pan Am until the airline ceased operations in 1991. Then known as Clipper Ocean Spray, this airplane is the last remaining of the once-great Pan American Clipper fleet.

 width=Above: Clipper Ocean Spray was part of Pan Am's historic Clipper fleet. Top. The story of GE and modern aviation are closely linked. Few symbols embody the connection more than the original GE flying testbed, a 49-year-old Boeing 747-100 that served as an airborne lab for engineers testing generations of new jet engines. Images credit: GE Aviation.

Among the many unique features of the 747 was a second passenger deck hidden inside the whalelike hump in the front of the fuselage. While later models would enjoy elongated upper decks, the 100’s was relatively short. This meant Pan Am had some trouble finding a use for it: Originally it was to be a piano bar, but the space proved too small for the passenger demand it generated. Pan Am then experimented with it as a first-class dining room with train-style Pullman suites, but those also failed for space reasons. Finally, Pan Am arranged the deck with first-class seats in a close configuration, ushering in the first business-class cabin.

Later in its life, the plane that became the testbed was one of the commercial aircraft chartered by the military to transport troops back from the first Iraq War, leading to an iconic photograph of a crewmember waving the American flag out of the flight-deck escape hatch after landing in Germany.

GE acquired the plane after Pan Am’s bankruptcy and used it for engine testing for 24 years. Ironically, because airlines didn’t want to part with their GE-powered 747s in the early 1990s, the only airplanes economically available for purchase were powered by Pratt & Whitney engines. GE refurbished the plane in North Carolina, modified the left wing to carry heavier GE engines and began flight testing out of Mojave, California. In 2003, the entire flight-test operation moved into its new hangar in nearby Victorville.

Certainly some may debate the claim, but it was as a GE testbed that the plane formerly known as Clipper Ocean Spray played its most important role, logging 3,916 testing hours with various GE Aviation products. The first engine test on N747GE was the original GE90, followed over the years by the CFM56 and CF34 engines, the GEnx for Boeing’s Dreamliner, the Engine Alliance GP7200 engine for Airbus A380 double-decker jets, two versions of the LEAP series engines, and the Passport for business jets.

 width=The plane formerly known as Clipper Ocean Spray logged 3,916 testing hours with various GE Aviation products, including two versions of the LEAP series engines developed by CFM International, a 50-50 joint venture between GE Aviation and Safran Aircraft Engines. CFM has received orders and commitments for more than 16,300 LEAP engines valued in excess of $236 billion at list price. Some 75 percent of all new single-aisle aircraft being delivered today are powered by LEAP engines. Image credit: GE Aviation.

The FAA require engines to undergo rigorous testing in real-world conditions before being certified for commercial use, a job Possert undertakes with obvious pride. Testing includes everything from basic performance like fuel burn to extreme flight conditions that most engines will never experience during service, such as the high angle of attack during aircraft stalls, zero-G operations, large sideslips and sustained flight in icing conditions. “These are things that are very difficult or impossible to do on the ground,” Possert explains. “You can’t define airplane engine performance unless you’re in flight at different altitudes and Mach numbers.”

The testbed was exceptionally well-maintained under GE’s care, Possert says. However, the lack of available parts began to catch up with it. For instance, the 747-100 uses a unique tire size, meaning GE had to special-order 50 at a time. In recent years, other parts became difficult or impossible to obtain. The 747-100 navigation systems also lacked many modern technologies, meaning that, if GE were so inclined, the plane couldn’t be flown into Europe under the EU’s navigation rules.

In short, through no fault of the testbed’s own, it was time to retire. GE acquired another testbed in 2010 — a 747-400, which remains in service and is currently testing the largest jet engine ever built, the GE9X

 width=GE acquired another testbed in 2010 — a 747-400 (with blue tail in the foreground), which remains in service and is currently testing the largest jet engine ever built, the GE9X. Image credit: GE Aviation.

The original testbed is the largest GE donation to the Pima Air & Space Museum, one of the largest privately funded nongovernmental air museums in the world. The museum’s holdings also include the RA-5C Vigilante, which was one of the largest aircraft to fly off U.S. carriers, powered by two GE J79-GE-10 engines; a Bell UH-1F Iroquois helicopter with one General Electric T58-GE-3 turboshaft; and an F/A-18 Hornet with two GE F404-GE-400 engines that was in service with the Blue Angels. All told, the museum has 26 aircraft featuring GE engines.

On Nov. 15, after guiding the testbed to an easy landing at Davis-Monthan Air Force Base just north of Pima, Possert brought the plane to a halt and announced, “Shutting down the engines for the last time.” He paused for a few seconds before moving the fuel levers to cutoff, realizing the significance of the moment. Then, using a chisel-point Sharpie brought along for the occasion, members of the flight crew signed their names to the interior of the cockpit, and walked alongside the plane as it was towed onto the Pima museum grounds and into the hands of history.

 width=Goodbye to all that. The two GE flying test beds cruising side by side over the Sierra Nevada mountains in 2015. Image credit: GE Aviation.