Just to clarify my earlier comment about the system “matching vertical speed”: I didn’t mean it was literally hard-coded to VS; it just behaves that way in practice when the aircraft climbs or is slewed quickly. The cabin tries to follow the airplane so aggressively that it feels like it’s tied directly to the climb rate, rather than being bounded by a sensible default rate.
Here’s a simple way to see what I’m talking about:
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Load the default 737 at around 10,000 ft.
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Set the cabin altitude to about 2,000 ft.
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Now slew quickly up to around 25,000 ft and watch how fast the cabin altitude climbs.
Instead of something like the older ~500 FPM behavior we had in MSFS 2020, the cabin altitude shoots up extremely fast. It’s much more aggressive than a real-world system and doesn’t respect a realistic default rate. On top of that, the valve only moves in whole-percent steps, so when it’s chasing that aggressive rate it tends to overshoot the target, then come back, then overshoot again. You can actually see the cabin altitude oscillate for a few passes before it finally settles near the selected value (and it doesn’t always land exactly on it).
I’ve seen third-party pressurization systems handle this more smoothly, and our own custom system for the Lear 35 in MSFS 2020 behaved better as well. There’s definitely room for improvement here, even if you don’t want to add a full rate-control knob. Just giving us a sane default rate (around 500 FPM, as in 2020) would already make the behavior much closer to real-world expectations and avoid the current “chasing” effect.
All of that said, I really do like the new modern pneumatic system overall. The way temperature, bleed air, and icing are all tied together with actual lines, valves, and connections is a big step forward and feels much more like a real system. We’ve gone through the setup carefully on our end and we’re definitely not missing any lines or connections—everything is hooked up as intended. The main issue isn’t missing plumbing; it’s the default control logic and rate behavior for the cabin pressure and valve movement. Fixing that would make an otherwise very promising system feel a lot more polished and believable.
On the “missing line/outlet” idea: we’ve actually ruled that out by testing side by side. We compared the default 737 (stock config) and our Lear 35 using the modern pneumatic system, running the same profile (e.g. 10,000 ft with a 2,000 ft cabin, then quickly up to ~25,000 ft). The overly aggressive cabin climb, overshoot, and oscillation all appear in the 737 itself, before our own setup is involved. That’s how we know this isn’t caused by a configuration mistake on our end.
Our pneumatic setup is behaving as expected (temps, packs, bleed sources, cabin volumes, etc.), and we’ve even added our own cabin rate control knob, which you’ll be able to see when we share our package. The main issue is the core control behavior: the default cabin rate is very high, and the valve only moves in 1% steps. That coarse stepping, combined with the aggressive rate, is what produces the overshoot and “hunting” around the target cabin altitude in both the 737 and our system.
If the default rate were closer to ~500 FPM and the valve resolution were smoother than whole-percent increments (or the controller internally smoothed), the system would feel much more realistic and would really let the strengths of the new pneumatic model show through.
