In situations like this, I always look at the professional pilots rumour site http://www.prune.org
Inevitably there are those posting there who agree that the aircraft should have landed at the nearest available airport, despite possible ground problems. These could have been significant, especially if the pilot assumed he might need to attempt a crash landing -
Why is YPLM [Learmonth] automatically considered by many as nearest suitable? It's isolated, limited RFF, limited hospital facilities, limited ATC, etc They weren't flying a Cessna. The AirAsia guys are thinking about all that and also considering Customs, hotels, maintenance and on it goes. Not to mention that the aeroplane is perfectly capable of flying on one engine. Many here are comfortable because they understand what it would be like at Learmonth (or somewhere similar in Oz) But it wouldn't have been that simple to these guys.
Although the rules mandate a landing at the nearest airport for pilots with major on board problems, there is sufficient leeway if he considers that be can return to the point of take-off and there are factors which make that the more ideal situation. That said, though, having decided against Learmonth, why did he twice ask the passengers to "pray"? That seems to indicate he thought the engine problem was far greater than merely vibration from a broken fan blade. And as another contributor to pprune.org points out -
For some engine failures, severe vibration may be experienced after the engine has been shut down, to the point where instruments are difficult to read. This vibration is caused by the unbalanced fan, windmilling at an engine speed close to an airframe’s natural resonance frequency, which amplifies the vibration. Changing airspeed and/or altitude will change the fan windmill speed and an airplane speed may be found where there will be much less vibration. There is no risk of airplane structural failure due to vibratory engine loads during this windmilling action.
Could this therefore be another case of an Air Asia pilot and his head office controllers simply not being aware that reduction of airspeed and/or altitude would have considerably reduced the vibrations? Did the pilot in fact attempt either or both manoeuvres after reporting the return to the air traffic controllers? Had he ever practised this in an A330 simulator?