Why weren't the Airbus A330 engines designed with a system to stop their fans? Why wasn't the Airbus A330 designed to stop its fans (with some kind of 'handbrake')?

To clarify, I am specifically talking about the aircraft that flew Air Asia flight D7237.

During the flight the aircraft suffered from a fan blade separation event and the the result was that the engine became unbalanced.

This was the result of the incident the plane was able to continue flying for over an hour and a half with the "moderate" vibrations and able to land safely (where the passengers were rewarded with a $20 voucher)

It's my understanding that the engine was immediately shut down, and that the cause of the vibrations was the fanblades freely turning as the plane moved very fast through the air (similar to blowing very hard into a turned off household fan)

But to me, it seems the whole situation could have been avoided if there was simply some kind of "brake" or 'locking' feature that prevented the fanblades from turning freely in the wind.

I feel as though there wouldn't exist another scenario where a plane could possibly experience more severe, prolonged vibrations than a windmilling event, and the windmilling event itself could be prevented if there was simply a way to lock the fanblades from moving freely.

The reason I say A330s in particular is because I am not aware of the features of every other jetliner, although I am aware some propeller engines can feather their blade parallel to the direction of airflow to prevent this.
Complexity and weight, what airlines hate most.

Has it been done before? Yup. A variant of the Convair B-36 Peacemaker was able to stop the windmilling when the jet engines were not needed (that variant had 6 piston engines and 4 jet engines).

(Source)


  The metal petals filling the inlet prevented the jets from turning in the wind as the B-36 cruised for long periods of time with them turned off. The petals retracted to allow the jet engines to be ignited for extra thrust during take-off and high speed dashes. A strut braces the nacelle against swinging from side-to-side.


Scaling this up for the big diameter engines for that very rare engine failure is not cost effective. Instead planes can survive, and are extensively tested for, vibration and flutter.

How rare is very rare?


  By the 1970s, advancing technology had set the stage for two-engine, turbine-powered airplanes to safely exceed the 60-min operating restriction [away from the nearest airport]. The result was ETOPS, which began in 1985 with 120-min diversion authority and the requirement for an average engine in-flight shutdown (IFSD) rate of just 0.05 per 1,000 engine-hours. With 180-min ETOPS authority, which followed in 1988, an even more stringent reliability target of just 0.02 IFSDs per 1,000 engine-hours was specified (Boeing, 2003).