My tuppence worth:
Many pilots seem to forget or don't realise that what they speak into their microphone is NOT what is heard by ATC and other traffic. The voice channels of airplane radios are frequency limited to about 300-3000 Hz, which is similar to that of a domestic telephone. Also, distortions caused by not using windshields, dirty microphones, faulty electronics, geography and atmospheric conditions, mean that what might sound perfectly clear to the person doing the speaking can actually be significantly distorted and garbled to the listener.
This is one reason why standard phrases were chosen - to be safely readable and recognisable through distortion and static etc.
When a frequency is quiet, I see nothing wrong with occasional banter - as long as it's kept brief. And 'good morning' and 'good bye' seem perfectly acceptable pleasantries - when there is time to do so.
In busy TMA, where lots of clearances and re-clearances are being fired off in machine gun fashion, that is NOT the time for anything other than standard ICAO phrases. Taking up RT airspace with non standard phrases that require re-transmissions and readbacks is not neccessary and could lead to dangerous situations.
When countries invent a non ICAO way of speaking between pilots and ATC; that may seem fine because everyone understands each other right? But it is a bad habit because then you might get a 'foreign' airliner or even a 'foreign' pilot in a domestic airliner, who might not get the gist and confusions could arise.
Speaking to a person whose first language is not English is another reason to stick to standard phraseology. While 'foreign' ATC will recognise and be able to converse in standard phraseology, there is absolutely no point talking fast and using colloquialisms to a non english speaker. I find that slowing down, speaking clearly and using standard phrases reduces read-backs to almost zero. It might seem slightly anal to do so, but in busy airspace it is the only way really.
Last edited by Uplinker; 25th Aug 2015 at 13:40.