I have long wondered about the continued usefulness of what some may now regard as the somewhat outdated concept of the Regional Pressure Setting (RPS) or Regional QNH. Its use is outlined in
AIP ENR 1.7 para.3.7 et seq., and
CAP410 (qv) also provides a helpful definition:
Regional Pressure SettingThe Regional Pressure Setting is a forecast of the lowest QNH value within an altimeter setting region. The values which are made available hourly for the period H + 1 to H + 2, are given in whole millibars.
However nowadays, many pilots seem to be unaware of the way the RPS is calculated and even its possible implications for their flight. There is just a tendency to set it anyway on departure. It will, of course, provide an over-safe (but therefore inaccurate) indication of terrain clearance within a given area for a period of up to 2 hours ahead; however there are traps for the unwary, who perhaps do not understand the problems of using it near, or especially under Controlled Airspace. The far better alternative, surely, is to use an appropriate aerodrome QNH for the flight? Since a locally obtained aerodrome QNH is not only relatively easy to obtain but undoubtedly more accurate in terms of correctly indicating height over terrain, perhaps we should question the point of continuing to routinely set and use the RPS?
While it is used in the theoretical calculation of the lowest usable FL in an airway which has a base near the TA, the setting itself is not actually used in the aircraft in that process. Regional Pressure Settings do have some use in the specialised areas of maritime reconnaissance operations and also in vertical separation of North Sea helicopter off-shore operations in the Anglia OSA (
ENR 1.15 para.1.5.5). However, in normal civilian use, with the possible exceptions of an extended non-radio flight remote from any airfield, over significant terrain and in a rapidly changing synoptic situation (when arguably one shouldn't be flying anyway!), or a flight when the pilot is so totally lost and could be anywhere in a large area (
AIC 21/2006), I really can't see the point in using the RPS.
What do you think ... ?
JD
