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Going Very High, Very Fast: Up in the Air With GE’s 747 Flying Test Bed Engineers

March 02, 2023

It’s hard to get bored when your day job involves climbing into a seat on the upper deck of a Boeing 747 and cruising over the Sierra Nevada mountain range on a regular basis. For Nate Kamps, principal engineer and test director for GE Aerospace’s Flight Test Operations team in Victorville, California, the work — and the view — never gets old.

“I can’t believe that I’m getting paid for this,” Kamps says. “We get to be the first people in the world to take new engines into the sky. And I get to look down at the Sierra Nevada and see places I’ve hiked to on the ground from a whole different perspective. Each time we get to go up, it’s a real privilege. It keeps me from getting complacent.”

That 747-400 that Kamps hitches a ride in is no ordinary airliner, either. It’s GE’s flying test bed, an airborne lab that the company has used since 2010 to test successive generations of new jet engines. (GE also operated a 747-100, previously owned by Pan Am, as a flying test bed for 24 years before retiring it to the Pima Air & Space Museum in Tucson, Arizona, in 2018.) Flight Test Operations (FTO) in Victorville, where the 747 flying test bed is based, is situated on the edge of the Mojave Desert. It serves as one of GE Aerospace’s main engine test hubs, in addition to Evendale and Peebles, in Ohio, and the company’s historic engine-making facility in Lynn, Massachusetts.

 

“That’s Why We Run the Tests”

Before an engine can be certified for commercial use by the FAA, it has to undergo rigorous testing in real-world conditions — that is to say, attached to the wing of a plane, rather than inside the controlled environment of an earthbound test cell. This is what keeps the 55 full-time team members at FTO busy working with engineering and design teams throughout GE Aerospace on a variety of engine programs. Indeed, over the course of their combined time in the air, the two 747s have certified 12 different engine models and multiple variants, including the GE90, CFM56-7B, CF34 (the -8C and-10E), GP7200,* GEnx (the -1B and -2B), LEAP** (the -1A, -1B and -1C), Passport and GE9X.

FTO team
Engineers Nate Kamps, Matty Putnam, and Kevin Murtha aboard the 747-400. Top: The flying test bed cruises past Alaska’s Denali, with a lenticular cloud over the summit. Images credit: Jason Chapman

Engineers Nate Kamps, Matty Putnam, and Kevin Murtha aboard the 747-400. Top: The flying test bed cruises past Alaska’s Denali, with a lenticular cloud over the summit. Images credit: Jason Chapman

Most testing takes place well before an engine is certified, though additional tests are sometimes required during the first few years an engine is in service as issues crop up in the field. Testing runs the gamut, from basic performance adjustments including fuel burn to extreme flight conditions, such as stalls and air starts, zero-gravity operations, large sideslips, and sustained flight in icy conditions. Since it was acquired in 2010, the 747-400 has logged more than 1,500 hours in the air.

“A lot of the work we do on the flight test is very empirical and we don’t have a great way to get the data we need on the ground,” says Kamps. “What we’re doing is developing and validating the control schedules that allow the engine to meet its performance goals, its certification requirements, and our internal requirements for how it has to behave in certain scenarios.”

Testing requires patience and the ability to make adjustments literally on the fly. This can often be the case with air starts — that is, restarting an engine while in flight, in a variety of scenarios involving different speeds and altitudes. “It can be a lot of trial and error,” says Kamps. On occasion they’ll run a test with the expectation that the engine will perform a certain way, only to discover different behavior, he notes. When that happens, they’ll look deeper into the data back at the FTO home base, where they can use more computing power, then make changes to the control schedules and take another crack at it in the air a day or two later.

“There’s two ways to look at that,” Kamps says. “One is, well, the engine didn’t behave the way we thought it would. On the other hand, that’s why we run the tests. Those findings are valuable. That’s the work we need to do to certify our commercial products.”

Fasten Your Seatbelts and Start Collecting Data

Once an engine has been elected for testing, it takes the team months to prepare. In fact, “it’s usually longer than the actual duration we’re conducting the test flights,” says Kevin Murtha, who works closely with Kamps as a flight test engineer. In addition to the regularly scheduled maintenance of the 747, which FTO must complete to meet air worthiness requirements just as any commercial operator would, the flight test team has a long to-do list: software upgrades; regular upkeep of the electrical power systems; installing a specialized pylon (the device that attaches the engine to the wing) for each test campaign; connecting all of the instrumentation inside the test engine to the onboard computers for monitoring and data collection; planning the tests; and structuring what the flights will look like.

Flying Test Bed Yosemite
A view of Yosemite Valley just ahead of the CF6 engine, with El Capitan and Half Dome visible. Credit: Jason Chapman

A view of Yosemite Valley just ahead of the CF6 engine, with El Capitan and Half Dome visible. Credit: Jason Chapman

“It can get intensive,” says Matty Putnam, the integration engineer who manages much of the scheduling, as well as hardware and workforce needs for each engine attachment. “Even though we can hang an engine in one day, it takes about a month to do all of our instrumentation and wiring, and to check everything.”

On flight test days, the flying test bed can get a little crowded. The test director sits with the two pilots in the cockpit on the flight deck — the upper deck of the jet, inside the 747’s famous hump. The rest of the test team, including FTO engineers and engineers from Evendale, takes up position on the main deck, where most of the coach-class seats have been removed to make room for racks of computers and individual workstations. There can be anywhere from eight to 20 people on board a typical flight. Only one forward galley remains (the rest were removed to make room for and help power the computer equipment), along with a couple of lavatories. “Most of our flights are on the order of six to seven hours, which would be a very long day if you didn’t have access to the lavs on board,” says Murtha.

Down on the main deck, “everyone’s monitoring something different,” says Putnam. “Some people are looking at performance data points. Some people are looking for specific test standards. Some are monitoring instrumentation.”

While all of that is going on, the test director is communicating with the pilots and the engineers, going over the different test procedures that will be run and “setting up each of those according to altitude and airspeed so that the test team can make the needed controls changes, throttle moves, and data collection,” says Murtha. 

“We’re continuously making sure that we’re seeing the results we’re expecting,” says Kamps. “If things are not going the way we thought they would, it’s my job to coordinate whether we need to make a change during the flight or put that test aside and come back to it on another flight. So I’m working with the chief test pilot and engineering team to figure out how we most efficiently use the airplane to get the data that we are after.”

 

Pretty Cool Job

This gets to why the 747 is such a solid platform for carrying out engine tests. First, the plane is powered by four engines, which provides a significant layer of safety. In addition to the test engine, “we have three other CF6 engines — that means three other sources of electrical power, three other sources of thrust, three other sources to drive the hydraulic systems,” says Kamps. “There’s lots and lots of redundancy.” The 747 also has a very large tail with a powerful rudder that can help correct any “asymmetric thrust,” such as when a test engine like a GE9X exerts more thrust than the CF6 on the opposite wing, causing the plane’s nose to yaw to one side. Finally, it has a very big “envelope” of airspeed and altitude capability. “It can go very fast and very high for a commercial airplane,” says Kamps, which enables the FTO team to put GE engines through all kinds of arduous tests.

 

Flying Test Bed Owens Valley
Over California’s Owens Valley (under low cloud cover), with the Sierra Nevada range to the left. Credit: Jason Chapman

Over California’s Owens Valley (under low cloud cover), with the Sierra Nevada range to the left. Credit: Jason Chapman

One such test took place on an airport tarmac in Fairbanks, Alaska, during the winter of 2020. The FTO team flew the plane north to run a series of procedures in very cold ambient temperatures, in this case minus 30 degrees Fahrenheit. Because the tests were run on the ground over multiple days, they had to keep the plane warm to avoid issues with the power system and pump heated air into the landing gear to protect the brakes and tires. They also had to rent heavy coats and boots rated for Arctic temperatures for the crew. “A unique series of conditions compared to what we’re used to flying out of the Mojave Desert,” notes Murtha. “It was definitely the coldest that I’ve ever been.”

“Thirty below zero may not sound appealing,” says Kamps, who was on that same trip. “But we also got to fly up the coast and see Alaska from the air. We flew right by Denali, and there was this beautiful lenticular cloud over the summit.”

Gliding past Denali. Flying over the top of Mount Whitney. Watching the sun go down over the Sierra Nevada. Not bad for a day at the office.

“It’s easy to lose perspective on how cool this job is,” Kamps adds. “I have a joke about how I have to share an office with two pilots, but it’s got the best view in the whole company.”

 

*The GP7200 is built by the Engine Alliance, a joint company of Pratt & Whitney and GE.

**LEAP engines are built by GE and CFM International, a 50-50 joint company between GE and Safran Aircraft Engines.