LONDON - BAE Systems says it is negotiating with the U.K. defense ministry on the potential of a third round of test flights for its Taranis unmanned combat air vehicle (UCAV) demonstrator.

The aircraft, which returned to the U.K. from its officially undisclosed test site - known to be in Australia - in May, has completed its second phase of flight tests, which saw the platform flown in its fully low-observable (LO) configuration during the winter of 2013-14.

The aircraft is currently undergoing maintenance at the company’s facility at Warton, Lancashire, and is waiting for a defense ministry decision on the third round of testing.

The first trials, disclosed by the U.K. defense ministry and BAE Systems back in February, were partly used to verify a conformal flight data system developed for the aircraft. To do that, the aircraft had been fitted with a flight data probe on the nose, which measured attitude, altitude and sideslip. To be able to fully test the low-observable aspects of the vehicle, this data probe was removed and the nose cleaned up, while engineers installed what they called “signature control variants” of various antennae. The flight control software was also adjusted. The aircraft was then taken through what company officials described as “realistic operational scenarios.”

“The ground-based and flight trials that have continued to meet all test objectives,” said Chris Garside, BAE Systems’s chief Future Combat Air Systems engineer, speaking at the Farnborough air show July 15.

BAE Systems did not comment on whether the vehicle was designed to avoid detection by VHF radar, although the planform - which has no edges or components that would be resonant at VHF - suggests that it is.

Nor did engineers confirm or deny the use of thrust-vectoring in the yaw axis, although Garside did say that the four inlay surfaces above and below the wings would be locked out "in certain flight regimes" and said the solution to providing yaw control with only two elevons was "within the flight control software. This is a stealth aircraft, and stealth aircraft are by definition difficult to fly."

Testing of sensors "was taken to a certain level" in the first two flight phases, Garside says. "Sensors were part of the original evaluation criteria," he says, "and we are currently discussing options for further trials with the defense ministry."

It is hoped that further trials will now feed into the joint U.K. and France UCAV feasibility study, announced by defense ministers of the two countries during talks at Brize Norton airbase at the end of January and also signed at Farnborough today. It is hoped that this deal will lay the building blocks of a future system, and possibly lead to the joint development of an Anglo-French UCAV.

Garside also revealed the levels of autonomy used on the aircraft, describing automatic taxi, landing and takeoff capabilities as well as the ability to generate an attack profile against targets, carry out post-bomb damage assessment, and if necessary, re-attack. During each process, the aircraft must be given a green light by the mission commander.

“During the sortie there is a level of action that the aircraft can decide on the best approach, but in respect of the rules of engagement, the system will always ensure there’s a ground commander in the loop,” Garside said.