I just looked up the RPS (ENR 1.7) and it’s the forecast lowest QNH in a large area for the next hour (there’s a map of the regions at ENR 6-18). By being a worst case, you’re less likely to fly into a hill, but more likely to fly into Alpha.
Edit: Peter got there first while I was proof reading 
gallois wrote:
Is there really such a huge hectopascal/mb variation between RPS and QNH in the UK as to make a significant difference between entering or not entering CAS?
Yes. I’ve never known the Barnsley RPS to be not less than 4 or 5 millibars lower than the actual QNH (in other words, enough to give 150 feet of error). Given all the low-lying CAS around Manchester, flying on the Barnsley RPS is likely to get you busted.
I won’t use the RPS any more: if the airspace near me is listed as a flight level, then 1013, and if the airspace is listed as an altitude, then the appropriate QNH.
Too bad the project to set the transition level at FL180 nationwide has been abandoned, despite being received positively.
If you google for the ASR topic, you find that with the 18000ft proposal this nutty idea was not going to go away. That’s what I have just found and it took me a while to find the above current map. They just proposed what looked like a different ASR map
Of course, if the RAF do a bust, it isn’t a problem.
Jacko wrote:
I’ve always assumed that ATC at towered fields blather on about wind and Q-codes just to fill the airwaves so that pilots don’t feel lonely. If people can’t land without all that Q-crap they should never have been sent on a PPL solo cross-country flight.
Yes, but no. When I have a 25kts wind at 500ft AGL/AAL, but the tower gives me a wind of 5 knots, I know to expect a respectable amount of windshear on short final. Forewarned is forearmed. Similarly, I’ve always found it useful to brief myself during the approach on the crosswind landing technique. Something like “the crosswind is from the right, so before touchdown, I’m going to add__right__ aileron and left rudder to decrab”.
Fuji_Abound wrote:
but there are good operational reasons why the RAF want them, and the RAF provide much ATSOCAS.Which are?
To confuse the enemy? 
Peter wrote:
If your Mode C shows in CAS, even by 100ft, then you are busted. … Bear in mind that a +100ft error (3mb or so) is enough to get you busted in the UK.
gallois wrote:
Is there really such a huge hectopascal/mb variation between RPS and QNH in the UK as to make a significant difference between entering or not entering CAS?
NealCS (post 38) made it to Gasco’s Bates Motel on only 32 feet, about 1 hPa: “I was invited onto one of these (UK) GASCO courses last year after a 9 second 32ft bust of the London TMA from below at a notorious pinch-point between Farnborough and the London TMA”
Yes, but no. When I have a 25kts wind at 500ft AGL/AAL, but the tower gives me a wind of 5 knots, I know to expect a respectable amount of windshear on short final.
How would you determine the wind strength and direction at 500ft?
Peter wrote:
Clearly it is possible, but I would not think the RPS-QNH difference is a big “Gasco filler”.
We wanted to address this very question, and altimetry more generally, for AIWG and are analysing 200 pilot reports from 2018. So far we have only looked at 120 of them, but among those altimetry was mentioned as a contributory factor four times:
So no RPS, but other similar errors.
flybymike wrote:
How would you determine the wind strength and direction at 500ft?
It is displayed on my PFD (and also on my MFD, but I watch my PFD more). It happens to be a Garmin G500, but don’t they all do that? GTNs can display it, too (I expect only when connected to an air data computer). It is one of the possible map data fields. On a steam gauges plane, well, I don’t know precisely, but I compare IAS (close enough to TAS for a non-mountain airport) to groundspeed (from the GPS) on downwind, base and final. Also, if I’m in a significant crab angle on final and the ground wind is weak, I know there’s a respectable difference with the ground wind.
VFR, I’ve been taught to turn final at about 500ft AAL, or alternatively about half the circuit height. Along with checking my speed and altitude, I have a glance at the wind speed and how different it is from the ground value (from ATIS or tower/AFIS/…). I don’t do a computation, I just notice any big difference.
IFR, I’m established on a stabilised approach, and usually on autopilot, at that point. Again, the convergence of the wind I have “right now” and the wind on the ground is one of the parameters I watch, albeit far more loosely than speed, lateral guidance, glideslope, etc.
I am not surprised that RPS is not a big factor because you need to do more than a local burger run to get caught by this, so only a small % of pilots would be at risk.
The ones at risk would be people doing longer trips, say Shoreham to Wellesbourne (150nm?), and doing them basically non-radio, and – to get busted – flying with Mode S. A very unusual profile; most Mode S flyers will be working the radio. Most non-radio flyers will be Mode A or txp-off.
So most of the potentially relevant crowd will not be in the stats because they won’t get caught.
So from the POV of reducing the fillup rate of the Gasco xmas stocking, the RPS etc is not a big thing. But from the POV of reducing the risk of a GA-CAT collision, it might be.
Re the wind stuff, yes wind (and the runway in use) is handy to know from the tower, but you don’t need the altimeter setting to land a plane in VMC.
To confuse the enemy?
Nooo; you would do that by moving the weekend to say Mon+Tues. Mr Putin knows that he can invade Europe easily by doing it on Sat+Sun This move would prevent any invasion because our forces would be totally prepared. Until a few years ago he could also do it in IMC…
