A harrier jet will fly past Rolls-Royce in Patchway today to mark the 50th anniversary of the Pegasus engine.

The engine, which powers the unique jump jet, pioneered Short Take Off Vertical Landing (STOVL) flight – dispensing with the need for a runway.

To mark the occasion Rolls-Royce, which employs 3,500 staff at Patchway, has invited members of the original Pegasus design team, including former technical director Dr Gordon Lewis, to attend a small ceremony at the factory.

The company will also be displaying the new Joint Strike Fighter LiftSystem, the legacy of the Pegasus and the eventual replacement for the Harrier.

To date, more than 1,200 engines have been produced and almost two million operating hours have been logged with the Harriers of the Royal Air Force, Royal Navy, US Marine Corps and the navies of India, Italy, Spain and Thailand.

The technology will take STOVL flight into the future on the world's biggest combat aircraft programme.

It is currently using the technology for the Lockheed Martin F-35 Joint Strike Fighter (JSF).

The company is teamed with Pratt & Whitney to develop the F135 STOVL Propulsion System for the planes.

The contract signed with Pratt & Whitney in December 2001, which covers the design and development work of the STOVL elements for the F135 during the System Development and Demonstration (SDD) phase of the program, is worth $1.5 billion to Rolls-Royce over 10 years.

Martin Fausset, Rolls defence managing director, said: "The 50th anniversary of the Pegasus provides us with the opportunity to look back and celebrate one of the most important programmes in the history of aero engine development in Bristol.

"It has been an active programme here for well over half of the site's lifetime and is still a source of great pride.

"The event also enables us to look forward to and showcase our work on the successor to Pegasus, the Rolls-Royce LiftSystem, which will take STOVL capability to the next level in the Joint Strike Fighter. Our position on JSF, the world's biggest combat aircraft programme, is a legacy of the innovation and hard work that began here in the late Fifties and the investment and development that followed."

● The Harrier will fly over Patchway at around 11am today.

PEGASUS FACTS:

Short Take Off Vertical Landing technology development dates back to the early 1950s, when military leaders foresaw the necessity for a new breed of defence fighters able to launch from bases with limited accessibility.

Project teams in the US and Europe studied a range of concepts, but only the Pegasus-powered Harrier survived to successfully enter service.

Its turbofan has four rotating nozzles, two on each side, that allows bypass air and exhaust gases to be sent in a downward direction.

The first STOVL patents were registered in 1956. The Pegasus ran in 1959, and the Pegasus-powered Hawker P1127 (to later become the Harrier) flew for the first time the following year.

The first operational squadron of STOVL fighters entered service with the RAF in 1969, and two years later, the US Marine Corps became the first export customer.

The Pegasus-powered Harrier first saw combat during the 1982 Falklands conflict in the South Atlantic.

It has since displayed its value in a number of combat scenarios, notably during the Gulf War, where STOVL capabilities allowed the AV-8B model to continue combat operations when its airfield was temporarily closed to other fixed-wing operations because a disabled aircraft blocked the runway.

AV-8Bs were able to continue takeoffs and landings from either end of the airfield.