Version: 1.6.34.0
Frequency: Consistently
Severity: Blocker
Bug description:
In the HYDRAULICS_SYSTEM_EX1 system, flap actuators continue to move even when hydraulic pressure is below the actuator’s defined MinimalPressure threshold, provided there is still fluid present in the connected line. This occurs even when all upstream shutoff valves are closed.
Expected behavior:
Once system pressure drops below the actuator’s MinimalPressure value, the actuator should no longer move, regardless of whether residual fluid remains in the hydraulic line. Closing a shutoff valve should also fully isolate the actuator and prevent further movement.
Actual behavior:
If any amount of fluid exists in the actuator’s supply line, the flap actuator continues to move even with:
- Engines off
- No active hydraulic pumps
- Reservoir empty
- System pressure below the defined threshold
- Upstream shutoff valves closed
If the hydraulic line is manually emptied (using the developer tools), flap movement stops as expected. However, once fluid has entered the line, closing valves afterward does not prevent the actuator from continuing to operate. The system appears to allow actuator motion based solely on the presence of fluid in the line, rather than valid pressure and authority.
This behavior has been reproduced consistently and observed in multiple aircraft. The CJ4 exhibits similar behavior, while the 737 appears to mask it due to very slow flap actuation speeds. This strongly suggests a systemic issue in the EX1 hydraulics logic rather than an aircraft-specific configuration problem.
This issue was previously raised in 2024 by Jim Stewart in the “Questions and Community Discussions” section (Hydraulics System EX1 behaviors), but it was not filed as a formal bug and therefore never received an official response. Given the impact, this is now being raised as a formal bug report.
Impact:
This is a blocker for accurate hydraulic system modeling. Aircraft developers cannot reliably prevent flap movement when hydraulic authority is lost. There is currently no viable workaround once fluid enters the line, even with correct valve logic and pressure thresholds configured.
This also was mentioned here last year.**
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Questions regarding HYDRAULICS_SYSTEM_EX1 behaviors - [MSFS 2024] Questions & Community Discussions - MSFS DevSupport