June 1982: That is when Honeywell Aerospace’s 757-200 test bed aircraft (now registered as N757HW) rolled off the line at Boeing’s plant in Renton, Washington. It was the fifth 757 ever produced, entering service with Eastern Airlines from February 1983 to January 1991. This ‘Flying Pencil’ (as 757s were nicknamed) then flew with Airtours International Airways starting in March 1995, according to planespotters.net, followed by MyTravel Airways starting in May 2002.
Honeywell acquired this 757 in 2005 to serve as its engine and instrument test bed, which explains the engine pylon jutting out of this aircraft’s upper forward starboard side. The company spent three years modifying it as a flying test bed with 25 seats, lots of onboard power, and room for all kinds of swappable equipment test stations inside. N757HW started flying test missions in 2008, and has been flying them ever since.
Although B757HW’s age is technically 40 years and counting, “we’ve made so many modifications and changes to this 757 over time that the only thing actually this old is its airframe,” said Captain Joe Duval, Honeywell Aerospace’s director of flight test operations. “It is configured to serve as a ‘generic flying test bed’. This means we can modify this 757 to test basically any aerospace product that we may be developing and have interest in, whether for pure research or certification.” According to Honeywell, their 757 is likely the only one in existence that has flown to more than 30 countries across five continents, conducted more than 800 flight tests, and logged more than 3,000 flight test hours.
Perfect for Testing Engines
The main reason Honeywell wanted this 757 was to have an aircraft large enough to mount and test its engines on. “This has traditionally meant turbojet and turbofan engines, but now it includes electric engines as well,” said Captain Duval. “The safest way to do this, when we’re making engines for business jets and general aviation, is to put them on an airplane that doesn’t require the propulsion from the engine under test. A 757 has two much larger engines for propulsion, which allows us to do whatever we need to do with the test engine mounted on the pylon without affecting the flying qualities or the performance of this aircraft.”
To date, N757HW has been used to test Honeywell’s HTF7000 jet engine series, which are used on business aircraft such as the Embraer Legacy 450/500. It has also been used to test the company’s TFE731 and TPE 331 turboprop engines, which are used on corporate and military aircraft.
Also Good for Aircraft Systems Testing
“Airborne weather radar, satellite communications, Controller Pilot Data Link Communications (CPDLC), equipment, flight management systems, navigation and other communication systems might be something you might think of as being simple as voice radio,” Captain Duval said. “But these things do need to be taken airborne to make sure they’re robust and safe for operation before we put them out there for the flying public. Fortunately, the uncluttered interior of the 757 makes it ideal for testing these systems, even though it’s not what people generally think of when they see that pylon sticking out of its fuselage.”
To date, the systems tested on N757NW include Honeywell’s IntuVue RDR-4000 and IntuVue RDR-7000 3D Weather Radar, next-generation flight management systems, JetWave and JetWave MCX in-flight Wi-Fi systems, and Aspire 350/400 satellite communication suites. More will be put through their paces in this test bed in the years to come.
The reason this 757 is able to test these and other systems so thoroughly has to do with its highly sophisticated data acquisition system. “It’s modular and generic, so that we’re always able to record Airplane State Data,” said Captain Duval. “This includes the air speed, altitude, bank and pitch angles, all synchronized with time of day. We can combine this information with data from any of the units/systems that we’re testing, whether that be an airborne weather radar, communication system, an engine, or what have you. We have a very capable data acquisition infrastructure system that is adaptable to whatever kind of unit/system we have on board, plus the real estate to house all of the computers and test stations we need inside this 757.”
A Beefed Up Aircraft
The stock version of the 757-200 was never intended to have a third engine attached to its fuselage adding weight and stress when activated in flight, let alone a cargo door inserted into it as well.
To cope with these challenges, “the aircraft’s metal is a little thicker because of the cargo door,” Captain Duval said. “Honeywell also added a pretty extensive crescent frame inside that strengthens the fuselage from above that cargo door up through that where the pylon sits. There are some really big, heavy attachment points for the test engine mounting that the pylon covers aerodynamically to make it look a little nicer. Those big attachment points are where the load is carried from the thrust and the weight of the engine and then distributed through the fuselage, so it’s not a problem.”
In order to minimize the third engine’s impact on the 757’s flight stability, Honeywell placed the third engine mounts as close to the center of the airplane. This keeps it from affecting the aircraft’s yaw axis and reducing its flyability.
“We had a goal of making sure that we didn’t reduce the operating envelope of the airplane, meaning we could still go as fast or as slow or as high as this 757 was originally designed to do,” said Captain Duval. “We needed and wanted to have that kind of performance envelope and we achieved that with all the design and effort that went into the installation. As well, there’s some pass-throughs that are built into the fuselage, just holes that we cap and we can use just depending on what we might be testing. And there’s lots of cabinets inside the aircraft that take all the instrumentation that might be going out to the engine, along with scanners and other things that are part of that data acquisition system.”
In order for this data acquisition system to work properly, N757HW needs to move massive amounts of data around; both on board and from the aircraft to the ground. “So we’ve made a lot of efforts in the last seven or eight years to enable high-speed bandwidth connectivity to the aircraft, using a few different SATCOM systems,” Captain Duval said. “After all, we make the terminal, the antenna, and the other SATCOM components that go into the airplane. We’re not making the satellites that we connect to, but we provide all the equipment such that if you have a wireless device inside the plane, you’re connected by Wi-Fi to the systems that we provide.
In a commercial airliner, this high-speed bandwidth would be used to support passenger internet access and in-flight entertainment. On N757HW, the purpose is to collect testing data and get it from the aircraft to the ground.
Not only is this connectivity useful for Honeywell’s testing procedures, but it could be something that enhances commercial aircraft availability going forward. “If you have a system that can describe the type of braking that was just used on a landing, and continually gather that data with the airplane being connected, then you could have a better way of doing predictive or preventive maintenance by changing a brake assembly when it needs it,” said Captain Duval. “This capability could also be connected to engines and other kinds of components on the airplane.”
Tough Test Conditions
Even though Honeywell’s 757 test bed is going on 41 years old, the company baby it. That’s because a flying test bed has to put the equipment being tested through extreme flying conditions to spot problems and remedy them back on the ground.
A case in point: “One important and exotic thing that we do with the airplane is wind shear testing,” Captain Duval said. “Our airborne weather radar has a predictive wind shear capability, which is important for safety when there are thunderstorms and things in the area that cause this wind shear phenomenon. So when we put this in an airplane, we need to certify it. We need to make sure that what the system is predicting is actual and true, so we have to go fly through wind shear events to develop a system that helps pilots avoid that.”
Because wind shear is dangerous to fly through, Honeywell does what it can to minimize the risks to its 757 crew and aircraft however it can. “We try to de-risk the activity as much as we can,” said Captain Duval. “We plan for a flight test area that’s not mountainous and doesn’t have other features or problems. This is vital for safety, because we have to go down to about a thousand feet above the ground and fly near or maybe even sometimes underneath heavy thunderstorms that are producing this wind shear phenomena to test the equipment. And so we’ll do that: We’ll fly through and see that the system’s predicting wind shear in a certain area and then, using that data acquisition system, gather all the data being generated as the aircraft flies through that wind shear event.”
“Again, this is something that pilots would normally be absolutely avoiding,” he noted. “But we are able to do that using a lower risk method because we’ve done all the work ahead of time to make sure we’re doing it safely.”
N757NW has also played a role in proving the viability of ad hoc wide area communications support for troops by taking part in Exercise Northern Edge. It was a multinational training exercise that brought together the United States Air Force, Navy, Marine Corps, the United Kingdom Royal Air Force (RAF), and the Royal Australian Air Force (RAAF).
In this exercise, the aircraft connected military forces with each other and the outside world through its multiple onboard SATCOM systems.
The Challenges of Age
The fact that Honeywell has done extensive modifications and constant servicing of its 757 test bed does not change the reality that this is a four-decades-old airframe. This makes finding parts a challenge, given that Boeing stopped manufacturing the 757 in 2004 after building 1,050 of them.
“I would say this: As long as there’s plenty of 757s flying around in other forms with other airlines and such, it’s less of a challenge right now,” said Captain Duval. “But as they get older and there’s less of them and there’s less parts available, people just don’t have the interest to keep these aircraft in service. When this happens, that will be even more of a challenge from its age.”
This being said, Honeywell’s 757 has proven itself to be a very, very reliable aircraft with lots of availability time. “We have a great group of mechanics and staff here that keep it up to date and keep the airplane operating,” Captain Duval said. “There’s also the fact that we only put a couple of hundred hours a year on it, when the 757 was built to fly in an airline and get many more hours flown on it in a year. We’re not inducing that same wear and tear on the aircraft, and updating it is — at least from the avionics perspective — actually easy for us because we’re using Honeywell equipment for the flight management system, the weather radar, Datalink, and anything else that might be a new kind of communication or navigation tool.”
As for the day when Honeywell needs to replace its 757 test bed? Given how well maintained this airframe is, plus the fact that B52 bombers made in the 1960s remain in service — as do some DC-3s built three decades earlier — it seems reasonable to assume that N757HW has lots of life left in it yet.
“We’re not looking for a replacement,” said Captain Duval. “We don’t feel like this is necessary yet. It will take us a few years to get through the analysis and figure out what we would want to replace it with, but we haven’t done that yet because we feel like we’ll be able to operate this airplane for quite a long time.”
Meanwhile, Captain Duval and his team are looking ahead to N757HW’s future missions. “In the foreseeable future, I expect to be testing Honeywell’s electrical propulsion systems using fuel cells, batteries, or other power generation capabilities that Honeywell is involved in creating,” he said. “So, we’re adapting the plane to support those activities. As well, there’s continued work with all the satellite communications systems being launched, and the terminals that access them.”
The bottom line: Honeywell’s 757 test bed has proven itself to be a reliable, flexible, and robust testing platform for the last 15 years, and its future looks just as promising.