NEW reports from the United States military's top weapons testing expert have raised fresh doubts about two of Australia's key future air power projects.

According to leaked documents the head of the Pentagon's operational test and evaluation office, Michael Gilmore, has raised major concerns about software flaws in the new F-35 Joint Strike Fighter and the sensors on board the Boeing P-8 Poseidon maritime patrol aircraft.

The eight Australian Poseidons to be based at Edinburgh near Adelaide are due in service by 2019 to replace the RAAF's P3C Orion maritime patrol planes.

Australia is set to buy between 50 and 100 of the Lockheed Martin built stealth fighter jets for up to $16 billion to replace the RAAF's F/A-18 Hornet fighters, but the Gilmore report has labelled the performance of the aircraft's software as "unacceptable".

Each F-35 carries more software code than a space shuttle and they are due in service with the US Marine Corps in mid-2015.

The first Australian jets were due in service by 2017.

According to the report the software problems will cause a further 13-month delay.

It also describes the fifth generation jet as less reliable, harder to maintain than expected and vulnerable to propellant fires from missile strikes.

The US Government will spend about $400 billion on the new jets for the Marines, air force and Navy.

The head of the F-35 program office Lieutenant General Chris Bogdan, who is due in Australia next month to discuss progress, told Reuters news agency that the report was factual but did not reflect the efforts underway to fix the software problems.

"The basic design of the F-35 is sound, and test results underscore our confidence in the ultimate performance that the United States and its international partners and allies value so highly," General Bogdan said.

"Of course, we recognise risks still exist in the program, but they are understood and manageable."

The Pentagon's chief weapons tester has also slammed the P8 Poseidon jet that is based on the Boeing 737 airliner.

According to Bloomberg, the report finds that the US Navy's version of the aircraft, the P-8A, is ineffective at both surveillance, and in detecting and destroying submarines.

That is the aircraft's primary role and the report highlights flaws in the aircraft's radar performance, sensor integration and data transfer.

It says that current version of the P-8A had not overcome "major deficiencies" identified more than a year ago.

It sensors include a multi-mode radar built by US firm Raytheon to detect aircraft, ships and submarines and a second belly-mounted radar that looks backwards.

When it detects a submarine the aircraft drops sonobuoys to detect metallic sounds under the water.

Originally published as Pentagon slams new Aussie jets