Ambient Pressure SPIKES

A:Ambient Pressure seem to have odd spikes on it, that seem to be related to “NO IDEA”

Normally on would not notice them, but if ambient Pressure is used to calculate some other more Visible variable, like Air speed,(in a more precise, study level simulation) then it becomes noticeably visibly on the Air speed Indicator…

Yes, one can FILTER the spiky Ambient Pressure, ( as we have been forced to do) but it might be better to eliminate the cause of the spikes in the first place,.

Green Plot is a Filter ambient Pressure (10% new, 90% old) - which obviously lags a little, but that is not as bad as spiking !!

Anyone any idea what is cause the very sharp spikes… Possible overly high frequency component Turbulence, something that also causes issues with the AP Pids !!


I wonder if the instantaneous turbulence acceleration has to do with it.

I am no weather expert, but I find it difficult to imagine large volumes of air, almost instantaneously accelerating up wards or downward as a result of convection… but I can imagine a Computer calculating such values, and not taking into account the mass of the air that is accelerating.

Some time ago I plotted out the vertical velocity of a light GA plane in MSFS, and found it had the same spiky, instantaneous acceleration and deceleration… and found I needed to also filter that to remove the high frequency component.

Note the time scale is in Seconds – can a C172 really accelerate up, then down, then up, then down , – all within I seconds – unless it had near zero mass ?

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So, let me ask a Blunt question,
What are the chances of Asobo tracking down & fixing these spikes ?

I suspect, even if they do, its going to be a LOW priority ?

So if Dev want to move forward now, with these spikes removed (or at least greatly reduced to a level where they do not cause “Perceived” issues) then for the time being we will have to do some of our own filtering to correct this issue…

Persoanally, I’m fine with that, although it does add another level of complication, as then we cannot directly use the sim’s A:vars, but instead, have to use our own “Filterered” values.

Although its not clear to me how we can FORCE our own Filtered Turbulence back into the sim (any suggestions, anyone ? )

I tried to reproduce this issue and I don’t have any spike behaviors in the tests I did.

I monitored A:AMBIENT PRESSURE, hpa and sampling at 30ms or 100ms there aren’t any samples that deviate unexpectedly. I used JS within the game to sample the data. Samples generally moved at 0.1hpa or so between samples, not the potentially up to 20 as seen above.

I tried in the default Asobo C172 G1000 and in our HPG H145 helicopter. In both cases I flew in live weather over Los Angeles. I turned Turbulence on to Realistic and still didn’t see any change in the sample variation.

If we can isolate this and create repro steps that would be the main hurdle to filing an actionable bug report.

1st of all THANK YOU Dave, for taking time to try to reproduce this.

It occurs in all panes that I have tested, so I do not think it is a Plane issue…

It only occurs over small, specific Pressure ranges, so to reproduce it, you have to monitor the ambient pressure, and you slowly climb, and then stop the climb when you start to see the spikes.

You will only be able to do this in AP, unless you have exceptional hand flying skills, so I strongly suggest you use the AP, and climb at a slow rate, till you hit a band of ambient pressure where this occurs.

As I type this , I realize that I should go back and check if the Interval between spikes is a function of speed, ie moving from one weather cell to another.

It is probably only an issue if you use ambient pressure in another calculation, whose result may then inherit the spikes, ie IAS, and you see a slight twitch on the airspeed.

Filtering the ambient pressure before you use it, can then reduce these spikes on your calculated output, to a negligible amount., but it would be nice to know why the spikes are there in the 1st place, and possibly have them removed at source, rather than having to filter them out

Looked it it again today… still not 100% identified under what condition it happens, but it does, with multiple planes, and in both real weather and weather presets…

But only at specific repeatable pressures bands.

100 pascal bands ? 95320 - 95420 clearly in 2nd screen shot

I set the helicopter to climb at 100fpm at 80kias from about 0 MSL to FL300 while taking 200ms pressure samples. No spikes that I can find so far. This would have been just default weather.

@N6722C what are you using within simconnect? Is it SIMCONNECT_PERIOD_SIM_FRAME and SIMCONNECT_DATA_REQUEST_FLAG_CHANGED? Maybe the issue is that I’m sampling at a regular rate and you’re getting samples delivered by the engine itself based on the internal data changing.

I am using an A:var plotting program called “LiveFlight"Data”
(Simconnect version)

have been using it for over a year and have never seen it falsely display any “Glitches or spikes”

Your Plot Y axis is probably far to Coarse, to show the spikes ?

Look at the scale I am using … The spikes are only about 10 pascals in amplitude, but that is enough to show a noticeable jump in any analogue gauge that is using ambient Pressure as part of its displayed calculation., UNLESS that input ambient pressure is SMOOTHED/FILTERED

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