Rolls-Royce's development of an engine for America's new Joint Strike Fighter (JSF) aircraft has hit more problems, fuelling a campaign by President Barack Obama's administration to remove the UK company from the $300bn (£180bn)project.
It appears that Rolls-Royce must redesign a key component, which critics claim is the latest in a string of failings that will increase costs and delay the introduction of the world's most high-tech jet.
The news comes at a critical time for the UK aerospace firm and its partner, General Electric, which will learn this week whether Congress will continue funding the engine's development for another year.
Rolls-Royce and GE are up against Pratt & Whitney (P&W) in the race to power the radar-evading JSF, with the winner estimated to earn about $100bn in revenues during the 30 years the aircraft is expected to be in operation.
The Pentagon believes P&W's engine is more advanced in development and is based on tried and tested technology. Last month Ashton Carter, the Pentagon's acquisitions chief, called the Rolls-Royce engine "disruptive" to the JSF programme.
But despite opposition from the Pentagon, and also from the Obama and Bush administrations, Congress has each year voted to approve money for the Rolls-Royce/GE engine, expected to need about $5bn in total.
Congress had argued that providing an alternative to P&W's engine was vital to maintain competition and get best value. But with the JSF project about $16bn over budget and with pressure on defence spending, Congress may now look for savings.
Loren Thompson, an analyst at America's Lexington Institute, believes Rolls-Royce's engine could be running as much as a year behind schedule. "GE and Rolls can no longer hold to their baseline schedule, and are being forced to replan their entire programme," he said.
A report by Lexington says Rolls-Royce managed just 52 hours of testing this year, because of "four major [engine] failures". The report said the engine would not be ready to benchmark against P&W until 2016. A Rolls-Royce source called this "rubbish".
Rolls-Royce's latest setback involves redesigning a component that helps hold the engine together. A spokesman for the Rolls-Royce/GE joint venture in the US said the re-design was not a particularly complex job and full testing would resume early next year. He said: "The [engine] programme continues to operate within budget and has met all major milestones on schedule ... The engine has accumulated over 550 hours of test time, with more than 800 hours of test since the programme began."
Making P&W sole supplier would anger the UK Government, which is buying up to 28 JSFs. Rolls-Royce is also sole developer of a "vertical" take-off engine for the JSF, to be used on the Royal Navy's two new aircraft carriers. This project is unaffected. But the most lucrative contracts are for conventional JSFs, with almost 3,000 expected to be built for the eight countries that have placed orders so far.