This minimizes the likelihood of asymmetric reverse thrust.

On landing, our pilots use idle reverse thrust (instead of full reverse thrust) and switch off one engine while taxiing where it is safe and practicable to do so.

This invention has the advantage that the flow past the rotor blades is less turbulent during thrust reversal, and the rotor blades thus generate a higher reverse thrust.

The invention provides a foldable propeller with improved performance, in particular high reverse thrust and low noise and vibrations.

In general terms, the shroud (30) includes a system for increasing the efficiency of the exhaust nozzle when acting as an inlet duct when the fan is providing reverse thrust.