Originally Posted by Standard Noise
IL Duce & 2SHEDS- If I have 2 vfr a/c both on a RIS, I tend not to give them standard separation, only traffic info after all it's an 'information' service. But I will want to know their respective altitudes which I am capable of working out from the pressure setting they are on. Maybe you both spend your time separating everything, personally, I don't!
The point is - how do you verify Mode C of an aircraft at an altitude if you do not ascertain that the pilot is reporting altitude based on a common reference? Surely you would, as a norm, have the aerodrome QNH set on the radar for aircraft below the transition altitude? (Apart from military units, which probably use Timbuktu QFE). I get the impression that you are saying that you will accept a level report based on any old setting and make a mental calculation to decide if it is within tolerance. Very professional - what conversion are you using, do you correct it for temperature and pressure, who has authorised that procedure, and what chance is there of you making an error if the Mode C is out of tolerance and you are busy? Furthermore, if you then use the Mode C for traffic information, it is likely to confuse the situation ("traffic at altitude 2700 ft" - pilot thinks "no, I'm at 2400 ft on the RPS").
It is quite evident from all the foregoing correspondence that in the context of most traffic at and below the transition level that is going from one aerodrome-based ATC unit to another for service, use of an RPS is not only a waste of time but confusing and potentially hazardous. It has its uses for low level traffic - military tactical, pipeline patrols etc - apart from that, it is a menace and should be limited to the lumpy bits of Wales and Scotland and the sea areas.