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feat(cpcu): Update low diff pressure warning trigger #10484

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f5a5c7e
Update low diff pressure trigger
FozzieHi Jan 17, 2026
751c4f6
Refactor update_low_diff_pressure_warning
FozzieHi Jan 19, 2026
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141 changes: 137 additions & 4 deletions fbw-common/src/wasm/systems/systems/src/air_conditioning/cabin_pressure_controller.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -66,6 +66,8 @@ pub struct CabinPressureController<C: PressurizationConstants> {
cabin_alt: Length,
cabin_vertical_speed: Velocity,
cabin_filtered_vertical_speed: LowPassFilter<Velocity>,
cabin_delta_p_rate: f64,
previous_cabin_delta_p: Option<f64>,
cabin_target_vs: Velocity,
outflow_valve_open_amount: Ratio,
safety_valve_open_amount: Ratio,
Expand All @@ -77,6 +79,7 @@ pub struct CabinPressureController<C: PressurizationConstants> {
is_in_man_mode: bool,
man_mode_duration: Duration,
manual_to_auto_switch: bool,
low_diff_pressure_warning: bool,

is_active: bool,
is_initialised: bool,
Expand Down Expand Up @@ -143,6 +146,8 @@ impl<C: PressurizationConstants> CabinPressureController<C> {
cabin_filtered_vertical_speed: LowPassFilter::new(
Self::VERTICAL_SPEED_FILTER_TIME_CONSTANT,
),
cabin_delta_p_rate: 0.,
previous_cabin_delta_p: None,
cabin_target_vs: Velocity::default(),
outflow_valve_open_amount: Ratio::new::<percent>(100.),
safety_valve_open_amount: Ratio::new::<percent>(0.),
Expand All @@ -154,6 +159,7 @@ impl<C: PressurizationConstants> CabinPressureController<C> {
is_in_man_mode: false,
man_mode_duration: Duration::from_secs(0),
manual_to_auto_switch: false,
low_diff_pressure_warning: false,

is_active: false,
is_initialised: false,
Expand Down Expand Up @@ -209,6 +215,7 @@ impl<C: PressurizationConstants> CabinPressureController<C> {
self.cabin_alt = new_cabin_alt;
self.reference_pressure = new_reference_pressure;
self.departure_elevation = self.calculate_departure_elevation();
self.update_cabin_delta_p_rate(context);

if !self.has_fault() {
self.outflow_valve_controller.update(
Expand Down Expand Up @@ -246,6 +253,7 @@ impl<C: PressurizationConstants> CabinPressureController<C> {
));
}

self.update_low_diff_pressure_warning();
self.is_in_man_mode = press_overhead.is_in_man_mode();
self.is_active = is_active;
}
Expand Down Expand Up @@ -573,11 +581,50 @@ impl<C: PressurizationConstants> CabinPressureController<C> {
}

pub fn is_low_diff_pressure(&self) -> bool {
// Only emit the signal if delta pressure information is valid
self.cabin_delta_p() < Pressure::new::<psi>(C::LOW_DIFFERENTIAL_PRESSURE_WARNING)
&& self.cabin_alt > (self.landing_elevation + Length::new::<foot>(1500.))
&& self.exterior_vertical_speed.output() < Velocity::new::<foot_per_minute>(-500.)
self.low_diff_pressure_warning
}

fn update_cabin_delta_p_rate(&mut self, context: &UpdateContext) {
let delta_seconds = context.delta_as_secs_f64();
let cabin_delta_p_psi = self.cabin_delta_p().get::<psi>();
self.cabin_delta_p_rate = if delta_seconds > 0. {
self.previous_cabin_delta_p
.map(|previous| (cabin_delta_p_psi - previous) / delta_seconds)
.unwrap_or(0.)
} else {
0.
};
self.previous_cabin_delta_p = Some(cabin_delta_p_psi);
}

fn update_low_diff_pressure_warning(&mut self) {
let in_descent = !matches!(
self.pressure_schedule_manager,
Some(PressureScheduleManager::DescentInternal(_))
);
let delta_p_psi = self.cabin_delta_p().get::<psi>();
let delta_p_rate = self.cabin_delta_p_rate;

let time_to_delta_p_zero_secs = delta_p_psi / -delta_p_rate;

let cabin_vs_fpm = self.cabin_vertical_speed().get::<foot_per_minute>();
let cabin_alt_diff_ft = (self.cabin_alt - self.landing_elevation).get::<foot>();
let time_to_cabin_landing_secs = cabin_alt_diff_ft / -cabin_vs_fpm * 60.;

let altitude_above_landing_ft =
(self.exterior_flight_altitude - self.landing_elevation).get::<foot>();

let activation_condition = time_to_delta_p_zero_secs < 90.
&& time_to_delta_p_zero_secs < time_to_cabin_landing_secs + 30.
&& altitude_above_landing_ft > 3000.
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@lukecologne lukecologne Jan 20, 2026

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Sorry, I missed this in my earlier comment. Of course the alt above landing condition must be removed here, as otherwise the warning would disappear below 3000ft above landing alt.

&& self.adirs_data_is_valid
&& in_descent;

if activation_condition && altitude_above_landing_ft > 3000. {
self.low_diff_pressure_warning = true;
} else if !activation_condition {
self.low_diff_pressure_warning = false;
}
}
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FozzieHi marked this conversation as resolved.

fn cabin_delta_p_out(&self) -> Pressure {
Expand Down Expand Up @@ -2085,4 +2132,90 @@ mod tests {

assert!(test_bed.query(|a| a.is_climb()));
}

#[test]
fn low_diff_pressure_triggers_in_descent() {
let mut test_bed = test_bed();

test_bed.command(|a| {
a.cpc.pressure_schedule_manager =
Some(PressureScheduleManager::DescentInternal(PressureSchedule {
timer: Duration::from_secs(0),
pressure_schedule: DescentInternal,
}));
a.cpc.adirs_data_is_valid = true;
a.cpc.landing_elevation = Length::new::<foot>(0.);
a.cpc.exterior_flight_altitude = Length::new::<foot>(4000.);
a.cpc.cabin_alt = Length::new::<foot>(6000.);
a.cpc
.cabin_filtered_vertical_speed
.reset(Velocity::new::<foot_per_minute>(-1000.));
a.cpc.cabin_pressure = Pressure::new::<psi>(11.);
a.cpc.exterior_pressure.reset(Pressure::new::<psi>(10.));
a.cpc.cabin_delta_p_rate = -0.02;
a.cpc.low_diff_pressure_warning = false;
a.cpc.update_low_diff_pressure_warning();
});

assert!(test_bed.query(|a| a.cpc.is_low_diff_pressure()));
}

#[test]
fn low_diff_pressure_remains_below_3000_ft() {
let mut test_bed = test_bed();

test_bed.command(|a| {
a.cpc.pressure_schedule_manager =
Some(PressureScheduleManager::DescentInternal(PressureSchedule {
timer: Duration::from_secs(0),
pressure_schedule: DescentInternal,
}));
a.cpc.adirs_data_is_valid = true;
a.cpc.landing_elevation = Length::new::<foot>(0.);
a.cpc.exterior_flight_altitude = Length::new::<foot>(4000.);
a.cpc.cabin_alt = Length::new::<foot>(6000.);
a.cpc
.cabin_filtered_vertical_speed
.reset(Velocity::new::<foot_per_minute>(-1000.));
a.cpc.cabin_pressure = Pressure::new::<psi>(11.);
a.cpc.exterior_pressure.reset(Pressure::new::<psi>(10.));
a.cpc.cabin_delta_p_rate = -0.02;
a.cpc.low_diff_pressure_warning = false;
a.cpc.update_low_diff_pressure_warning();
});

test_bed.command(|a| {
a.cpc.exterior_flight_altitude = Length::new::<foot>(2500.);
a.cpc.update_low_diff_pressure_warning();
});

assert!(test_bed.query(|a| a.cpc.is_low_diff_pressure()));
}

#[test]
fn low_diff_pressure_rejected_when_time_to_zero_is_too_long() {
let mut test_bed = test_bed();

test_bed.command(|a| {
a.cpc.pressure_schedule_manager =
Some(PressureScheduleManager::DescentInternal(PressureSchedule {
timer: Duration::from_secs(0),
pressure_schedule: DescentInternal,
}));
a.cpc.adirs_data_is_valid = true;
a.cpc.landing_elevation = Length::new::<foot>(0.);
a.cpc.exterior_flight_altitude = Length::new::<foot>(4000.);
a.cpc.cabin_alt = Length::new::<foot>(6000.);
a.cpc
.cabin_filtered_vertical_speed
.reset(Velocity::new::<foot_per_minute>(-1000.));
a.cpc.cabin_pressure = Pressure::new::<psi>(11.);
a.cpc.exterior_pressure.reset(Pressure::new::<psi>(10.));
a.cpc.cabin_delta_p_rate = -0.005;
a.cpc.low_diff_pressure_warning = false;
a.cpc.update_low_diff_pressure_warning();
});

assert!(!test_bed.query(|a| a.cpc.is_low_diff_pressure()));
}
}