Airbus operators need to check RATs warns EASA.

The action comes after Hamilton Sundstrand, a subsidiary of United Technologies, reported a failure during a wind tunnel test of a balance weight fastening screw on a RAT turbine cover - 

"After investigation, it has been discovered that a batch of screws, which are used to attach the balance washers of the Hamilton Sundstrand RAT turbine assembly, have not been subject to the correct heat treatment and are consequently exposed to potential fracture," EASA states.

If the screws fracture and release the balance weights, EASA says the RAT vibrations can increase and possibly cause "detachment of RAT parts and consequent loss of RAT functionality".

In the worst case, the problem could leave pilots with no control over an aircraft if all engines were to flame out, says EASA. Airbus uses RATs to power the aircraft's essential systems in the absence of engine power.