|Quoting bri2k1 (Reply 46):|
At the moment the LC gives a LUAW clearance, that runway can't be used for anything else until that traffic enters the runway and then departs. If a pilot thinks (s)he's just heard "blah blah WAIT" and sits there at the hold line, safety is compromised. The controller could cancel the clearance and allow an arrival to continue, but if the pilot suddenly remembers what LUAW means and taxis ahead, now we've got an incursion, and we were just cleared onto the runway a few seconds ago.
How is this any different from the regional dialect? As has been commented, there have been cases of pilots confusing "hold short" and "position and hold" due to poor readability.
But "line up and wait" has three advantages:
1) "wait" isn't used in any other standard phraseology and so isn't going to be confused by anyone who knows better.
2) since "line up and wait" would only be used when giving clearance for entering the active, mis-hearing and holding position will mean the pilot just sits in the safety of the taxiway rather than under the regional dialect where a hold short instruction could be misheard as a clearance to enter.
3) it standardises the phraseology with what the rest of the world use, eliminating confusion caused by differing regional dialects.
There may be some pangs with the introduction as all changes have, but in the long term, it will be more optimal.