Rolls-Royce acknowledges it is working to identify a flaw in the AE3007 powerplant that has led to at least two in-flight engine shutdowns and emergency landings of the US Air Force’s Northrop Grumman RQ-4A Global Hawk unmanned air vehicles.
The manufacturer says the flaw is triggered by how the engine reacts to ingesting disturbed air at high altitude, but declines to identify the precise problem. A root-cause analysis is being prepared for delivery to Northrop within a few weeks, says Dennis Jarvi, president of Rolls-Royce Defense North America. “We’re several weeks away from coming up with a real answer,” he says.
The performance of the AE3007 at the peak of the altitude envelope for the RQ-4A – somewhere above 65,000ft (19,800m) – has been scrutinised for some time. The AE3007 was originally developed for the Embraer ERJ-145 regional jet, which operates below 41,000ft and lacks the Global Hawk’s 24h endurance requirements.
“You don’t really get the margin to react to disturbances” occurring in the thin air above 65,000ft, which, says Jarvi, “causes any anomaly to be magnified”.
R-R had just finished developing a software upgrade to improve the AE3007’s performance at high altitude when the two shutdown incidents occurred earlier this year. That upgrade has been installed on all deployed RQ-4As so far, while the other Global Hawk airframes are operating under “modest” altitude flight restrictions, says Jarvi.
Little is known about the details of the two engine shutdown incidents. An RQ-4A undergoing a check flight at Edwards AFB, California glided to a safe emergency landing in July. Another Global Hawk lost engine power during an operational flight in south-west Asia. The engine flaw led to a brief fleet-wide grounding in mid-August.
- The US Air Force and Navy last week conducted a Congressionally directed flight demonstration using the Global Hawk’s on-board radar to track an airborne target – a Raytheon Beech C-12 King Air – for the first time.
STEPHEN TRIMBLE/WASHINGTON DC
Source: Flight International
