Top Image: GE Aviation acquired its original flying test bed (red stripe) two decades ago. That plane, called Clipper Ocean Spray, was the 16th Boeing 747 ever built and flew for two decades in Pan Am livery. Earlier this year, it was testing the new Passport engine GE developed for Bombardier's Global 7000 and Global 8000 business jets. Above: GE's two flying test beds over Sierra Nevada. All image credits: Wolf Air Vectorvision/GE Aviation

A Passport engine on wing of GE's original flying test bed is powering through tests.

GE flies the planes from its Flight Test Operations Center in Victorville, Calif., located on the edge of the Mojave Desert.

GE bought its new flying test bed (blue tail) from Japan Airlines. After two decades in commercial service, GE spent 14 months puling out seats, rewiring the plane and installing state-of-the art avionics. The first test engine on wing was the next-generation LEAP.

The flying test beds and filled with computers and test equipment. The new plane holds nearly 900 miles of wiring and fiber optic cable.

The cables connect sensors embedded in the engines to rows of computers inside the economy cabin and help engineers analyze terabytes of complex data in flight.

The fiber optic cable will stream digital data from some 1,700 instruments and sensors monitoring thrust, temperature, fuel consumption and other readings from the engine.

The LEAP was developed by CFM International, a joint company between GE and France’s Safran (Snecma). Even though the engine won’t enter service until 2016, it’s already the best selling jet engine in GE’s history. CFM has have received more that 7,000 orders and commitments for the LEAP valued at more than $125 billion.

There will be three versions of the LEAP engine: LEAP-1A for the Airbus A320neo, LEAP-1B for Boeing 737MAX, and LEAP-1C for the Comac C919. It's the first engine with GE technology that contains 3D-printed parts and components from a groundbreaking material called ceramic matrix composites.

GE engineers reinforced the wing structure of the new test bed, drilled new holes in the fuselage for extra cables and modified the wing leading edge around engine No. 2 (the engine on the left side closest to the body).

The changes will allow engineers to attach to the wing any of the new engines the company is developing, including the giant GE9X engine. With 132 inches in fan diameter, the GE9X is largest jet engine ever designed.

Besides the test engine, the new flying test bed uses GE's CF6 engines, the same kind that power Air Force One.

New GE jet engines must pass a litany of hardships on the test stand — from bird strikes to hailstorms — before they get to take to the air.But even then they are not finished. One of the steps required to win FAA certification actually looks like fun — though the engines might object. It involves flights on GE’s Flying Test Beds. GE has two of them, each one a converted Boeing 747 packed with computers, electronics and other gear. The newer one, which GE acquired in 2011, can safely climb as high as 45,000 feet, some 5,000 feet above maximum cruising altitude.Earlier this year, when GE was testing LEAP and Passport engines, the engineers invited a photographer in a separate plane to join them for test flights over California’s Sierra Nevada. Take a look at the haul he brought back.