It is common for aerospace companies to use modified commercial aircraft as specialized testbed aircraft to test new technologies before integrating them onto new aircraft. Not only do Boeing and Airbus maintain fleets of commercial aircraft used to develop next-generation commercial aircraft, but aerospace defense companies also maintain commercial aircraft to develop next-generation fighter jets. One of the most notable modified testbed aircraft today is the modified Boeing 757-200 'Excalibur' used to help develop the Global Combat Air Programme (GCAP)/Tempest sixth-generation fighter jet.

Somewhat confusingly, the names Excalibur and Catfish have been applied to multiple separate testbed aircraft, as it seems names are in short supply. There is a 2Excel Excalibur (the one of interest here), Airbus Excalibur, Dassault Excalibur, Lockheed Catfish (757), Airbus CATFISH (A340), and Chinese Tu-204 'Catfish' as an unofficial nickname. Additionally, the US Air Force and Navy have/had independent fighter jet programs both named NGAD, and the Europeans have (had) two unrelated programs called FCAS (one is part of GCAP). Here is what to know about GCAP's Excalibur and its role in the world's leading export-oriented sixth-generation fighter jet program.

Why A 757 Is Used As A GCAP Testbed

In July, major GCAP/Tempest contractor Leonardo UK published an extensive piece on the Boeing 757-200 'Excalibur' testbed aircraft and its role in developing the fighter jet. The effort is part of a $146 million contract led by Leonardo UK. Leonardo explains that next-generation fighters come with an amalgam of complex sensors, data systems, and autonomy. Validating their designs requires more than ground-based computer modeling; they need testing on testbed aircraft.

This is where the modified Boeing 757-200 Excalibur flight test aircraft (FTA) comes in. Excalibur is being developed by Leonardo and 2Excel as part of Team Tempest, which is a UK Industry and MoD partnership to develop technologies for the future fighter. Leonardo UK explains, "Airborne testing will be a fundamental enabler for the programme with the ability to fly in representative environments and perform real-world tests that cannot be replicated on the ground via simulation and modelling alone."

It states that while computer modeling and simulations are powerful, they can't give the fidelity achieved by airport test assets. Excalibur is designed to bridge the gap between concept development and a deployable capability. The 757-200 was chosen for its size, performance, and adaptability.

A Phased Approach & Systems Installed

Excalibur's modifications are ongoing, but it has already been seen flying with side pods and an extensively modified nose. After it receives clearances approving its modified structure, development is to shift to onboard system testing. From there, the Boeing 757-200 will transition to hosting "technical data packages to support GCAP development." Excalibur also boasts massive onboard computing power.

The Flying Pencil 757 will verify technologies like electronic warfare, communications, and electro-optic/infrared. Some of these technologies are to be part of GCAP's Integrated Sensing and Non-Kinetic Effects (ISANKE) and Integrated Communications Systems (ICS) to allow the aircraft to have a next-generation integrated sensing, fusion, and self-protection capability. More complex systems (e.g., radar) will be fitted and tested on Excalibur as the program develops.

Another ability Excalibur has is that of a regular transport aircraft ferrying teams flying between relevant countries for testing. During the 2026 Farnborough Airshow, the general manager of the GCAP Electronics Evolution team and director of major air programs at Leonardo (Andrew Howard) spoke of future modifications for Excalibur. These will include the advanced Multi-Function Radio Frequency System (MFRFS) radar, electronic warfare, infrared search-and-track, and electro-optical systems.

De-Risking & Developing Teaming Capabilities

Commercial aircraft, like the Boeing 757, allow engineers to test, validate, and develop equipment before integrating it into highly confined aircraft like fighter jets. They help to de-risk programs, grappling with issues like size, weight, and power constraints. Leonardo UK goes so far as to say, "In fact, the real advancement and innovation here is integration, ensuring that systems share data within the integration layer."

Excalibur helps live sensor networking, data link testing, and multi-system interactions for real-world insights. It also provides a "significant opportunity to deepen understanding of the sixth-generation battlespace." Yet another advantage is that "spiral developments can be incorporated as the programme progresses." It helps the development of autonomous and uncrewed teams, which is going to be a core part of GCAP.

Like other next-generation fighters, GCAP is to operate alongside Collaborative Combat Aircraft (CCAs). The Boeing 757 provides "the perfect platform to prove that the GCAP platform can control CCAs and fuse their sensing data in realistic conditions. Excalibur will therefore allow engineering teams to perform these experiments at scale as part of the future air combat ecosystem."

Excalibur's Iberian (& TUI Airways) Backstory

According to Planespotters.net, Excalibur was originally delivered to Spain's Iberia flag carrier in 2000 (then registered EC-HIR). The aircraft is MSN 29308, is powered by Rolls-Royce turbofans, and is now 26 years old. After flying for Iberia for five years, the aircraft flew for Turkey's Atlasjet (registered as TC-OGT) and, from there, was leased to Ethiopian Airlines, Eritrean Airlines, and Saudi Arabian Airlines, while also being flown by Atlasjet.

In 2012, it was transferred to the UK's Titan Airways (registered G-POWH) and then leased by Titan to Jet2 in 2016. Finally, it was acquired by 2Excel Aviation in 2023 for use as a testbed. It was registered as G-FAI. But Excalibur is just one of two 757-200s 2Excel acquired for the program. The other Boeing 757-200 was dismantled to support Excalibur.

That aircraft was 27.6 years old at the end of its life. It was built in 1995, bore MSN 27234, and was delivered to Britannia Airways in 1995. The aircraft was only ever registered G-BYAW. It was operated by Britannia Airways. Britannia Airways rebranded itself as Thomsonfly (later Thomson Airways and TUI Airways) and was the sole operator of the aircraft until the airline withdrew it from use in 2019. It was stripped for parts at England's Lasham Airfield after 2Excel acquired it in 2020.

One Of Many Specialized Testbed Aircraft

In addition to supporting the development of GCAP, Excalibur is also supporting capability enhancements for the Eurofighter Typhoon and the F-35 Lightning II. Elsewhere in Europe, an Airbus A320 Advanced Technology Research Aircraft (ATRA) has been modified as a testbed for the Typhoon's future Common Radar System (ECRS) Mk. 1 and to accelerate the maturation of a new AESA radar.

Perhaps the most famous modified commercial aircraft for a fighter jet program was the infamous N757N 'Catfish'. It was the world's first Boeing 757 and was later extensively modified to deliver the F-22 Raptor. The Lockheed CATBird (Boeing 737-300) was used in the development of the F-35 Lightning II. Boeing's 737 Flying Test Bed has supported development and risk reduction for numerous programs, including the F-15EX Eagle II, T-7A Red Hawk, and other military aircraft.

China is known to have similar modified commercial aircraft for its fighter jet programs, including a Tupolev Tu-204 'Catfish.' China generally doesn't comment or publicly disclose these programs. NASA has had many modified testbed aircraft, including the Boeing 737-100, NASA 737 Airborne Research Test System (ARTS), the NASA 757 ARIES Boeing 757-200, NASA DC-8 Airborne Science Laboratory DC-8-70, and the NASA MD-90 X-66 Testbed MD-90.

GCAP Is Only Export-Oriented 6th-Gen Fighter

GCAP/Tempest is being developed by the UK's BAE Systems, Italy's Leonardo, and Japan's Mitsubishi as the world's only export-oriented 6th-generation fighter jet program. The USAF's F-47 is expected to be very specialized and specifically designed for the Air Force's Asia-Pacific requirements. It is unclear if the US will even allow it to be exported. The US Navy is also developing a next-generation carrier-based fighter dubbed the F/A-XX.

Meanwhile, there haven't been any concrete updates on Russia's MiG-41 interceptor program in years, leading some to assess it is not a fully funded program. Many analysts believe Russia is more concerned with building its mainstay Flanker series of fighter jets and maturing its Su-57 Felon to win its current conflict than diverting limited resources into a far-off fighter intended to win a future conflict.

The primary competition to GCAP was the rival European FCAS sixth-generation fighter jet program. However, after years of bitter industrial disputes, Germany terminated the program with France (and Spain). France's Dassault has said it will develop a next-generation fighter jet independently, but this is expected to be a scaled-down carrier-based fifth-generation fighter. China's new J-36 in development is not expected to be exported. All this means that for now GCAP is the only fully funded and credible next-generation export-oriented fighter jet in development.