diff --git a/.github/CHANGELOG.md b/.github/CHANGELOG.md
index fa6db1e8931..80b3d03c34e 100644
--- a/.github/CHANGELOG.md
+++ b/.github/CHANGELOG.md
@@ -12,6 +12,8 @@
 
 ## 0.15.0
 
+1. [A380X/GPWS] Fix mode 4 logic - @Jonny23787 (Jonathan)
+
 ## 0.14.0
 
 1. [A380X/FMS] Fix speed margins being displayed in the wrong place for a Mach target - @BlueberryKing (BlueberryKing)
diff --git a/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/Climb.flt b/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/Climb.flt
index cd197c9a621..0fa6315172c 100644
--- a/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/Climb.flt
+++ b/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/Climb.flt
@@ -267,6 +267,8 @@ A380X_EFIS_R_TRAF_BUTTON_IS_ON=1
 A32NX_FAC_1_PUSHBUTTON_PRESSED=1
 A32NX_FAC_2_PUSHBUTTON_PRESSED=1
 A32NX_GEAR_LEVER_POSITION_REQUEST = 0
+A32NX_GPWS_GROUND_STATE=0
+A32NX_GPWS_APPROACH_STATE=1
 A32NX_ISIS_BUGS_ALT_ACTIVE:0=0
 A32NX_ISIS_BUGS_ALT_ACTIVE:1=0
 A32NX_ISIS_BUGS_ALT_VALUE:0=100
diff --git a/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/approach.FLT b/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/approach.FLT
index 5c2aec9597b..4c7b2e43da0 100644
--- a/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/approach.FLT
+++ b/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/approach.FLT
@@ -301,6 +301,8 @@ A32NX_FAC_2_PUSHBUTTON_PRESSED=1
 A32NX_FMS_SWITCHING_KNOB=1
 A32NX_FWC_SKIP_STARTUP=1
 A32NX_GEAR_LEVER_POSITION_REQUEST = 0
+A32NX_GPWS_GROUND_STATE=0
+A32NX_GPWS_APPROACH_STATE=1
 A32NX_HYD_ELECPUMPLOCK_TOGGLE=0
 A32NX_INITIAL_FLIGHT_PHASE = 5
 A32NX_ISIS_BUGS_ALT_ACTIVE:0=0
diff --git a/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/apron.FLT b/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/apron.FLT
index ec4f223d6c1..83b3768651b 100644
--- a/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/apron.FLT
+++ b/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/apron.FLT
@@ -297,6 +297,8 @@ A32NX_GEAR_CENTER_POSITION = 100
 A32NX_GEAR_LEFT_POSITION = 100
 A32NX_GEAR_LEVER_POSITION_REQUEST = 1
 A32NX_GEAR_RIGHT_POSITION = 100
+A32NX_GPWS_GROUND_STATE=1
+A32NX_GPWS_APPROACH_STATE=0
 A32NX_HYD_ELECPUMPLOCK_TOGGLE=0
 A32NX_ISIS_BUGS_ALT_ACTIVE:0=0
 A32NX_ISIS_BUGS_ALT_ACTIVE:1=0
diff --git a/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/cruise.FLT b/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/cruise.FLT
index adcf6a26d3e..e621e0e54f9 100644
--- a/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/cruise.FLT
+++ b/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/cruise.FLT
@@ -320,6 +320,8 @@ A32NX_FAC_2_PUSHBUTTON_PRESSED=1
 A32NX_FMS_SWITCHING_KNOB=1
 A32NX_FWC_SKIP_STARTUP=1
 A32NX_GEAR_LEVER_POSITION_REQUEST = 0
+A32NX_GPWS_GROUND_STATE=0
+A32NX_GPWS_APPROACH_STATE=1
 A32NX_HYD_ELECPUMPLOCK_TOGGLE=0
 A32NX_INITIAL_FLIGHT_PHASE = 3
 A32NX_ISIS_BUGS_ALT_ACTIVE:0=0
diff --git a/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/hangar.flt b/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/hangar.flt
index e4a077a0c1b..7b5958cd8e4 100644
--- a/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/hangar.flt
+++ b/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/hangar.flt
@@ -272,6 +272,8 @@ A32NX_GEAR_CENTER_POSITION = 100
 A32NX_GEAR_LEFT_POSITION = 100
 A32NX_GEAR_LEVER_POSITION_REQUEST = 1
 A32NX_GEAR_RIGHT_POSITION = 100
+A32NX_GPWS_GROUND_STATE=1
+A32NX_GPWS_APPROACH_STATE=0
 A32NX_HYD_ELECPUMPLOCK_TOGGLE=0
 A32NX_HYD_ELECPUMPY_FAULT=0
 A32NX_HYD_ELECPUMPY_TOGGLE=1
diff --git a/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/runway.FLT b/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/runway.FLT
index c635446df5e..ef534e02e6e 100644
--- a/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/runway.FLT
+++ b/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/runway.FLT
@@ -333,6 +333,8 @@ A32NX_GEAR_CENTER_POSITION = 100
 A32NX_GEAR_LEFT_POSITION = 100
 A32NX_GEAR_LEVER_POSITION_REQUEST = 1
 A32NX_GEAR_RIGHT_POSITION = 100
+A32NX_GPWS_GROUND_STATE=1
+A32NX_GPWS_APPROACH_STATE=0
 A32NX_HYD_ELECPUMPLOCK_TOGGLE=0
 A32NX_ISIS_BUGS_ALT_ACTIVE:0=0
 A32NX_ISIS_BUGS_ALT_ACTIVE:1=0
diff --git a/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/taxi.flt b/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/taxi.flt
index c06b139684b..5ba5e22ee2b 100644
--- a/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/taxi.flt
+++ b/fbw-a380x/src/base/flybywire-aircraft-a380-842/SimObjects/AirPlanes/FlyByWire_A380_842/taxi.flt
@@ -315,6 +315,8 @@ A32NX_GEAR_CENTER_POSITION = 100
 A32NX_GEAR_LEFT_POSITION = 100
 A32NX_GEAR_LEVER_POSITION_REQUEST = 1
 A32NX_GEAR_RIGHT_POSITION = 100
+A32NX_GPWS_GROUND_STATE=1
+A32NX_GPWS_APPROACH_STATE=0
 A32NX_ISIS_BUGS_ALT_ACTIVE:0=0
 A32NX_ISIS_BUGS_ALT_ACTIVE:1=0
 A32NX_ISIS_BUGS_ALT_VALUE:0=100
diff --git a/fbw-a380x/src/systems/systems-host/Misc/LegacyGpws.ts b/fbw-a380x/src/systems/systems-host/Misc/LegacyGpws.ts
index b78b2a3a918..b87a5c03933 100644
--- a/fbw-a380x/src/systems/systems-host/Misc/LegacyGpws.ts
+++ b/fbw-a380x/src/systems/systems-host/Misc/LegacyGpws.ts
@@ -1,9 +1,16 @@
 // @ts-strict-ignore
-import { Arinc429SignStatusMatrix, Arinc429Word, NXDataStore, UpdateThrottler } from '@flybywiresim/fbw-sdk';
+import {
+  Arinc429SignStatusMatrix,
+  Arinc429Word,
+  NXDataStore,
+  NXLogicConfirmNode,
+  NXLogicTriggeredMonostableNode,
+  UpdateThrottler,
+} from '@flybywiresim/fbw-sdk';
 import { FmgcFlightPhase } from '@shared/flightphase';
 import { LegacySoundManager, soundList } from 'systems-host/Misc/LegacySoundManager';
 import { A380X_DEFAULT_RADIO_AUTO_CALL_OUTS, A380XRadioAutoCallOutFlags } from '../../shared/src/AutoCallOuts';
-import { EventBus, SimVarValueType } from '@microsoft/msfs-sdk';
+import { EventBus } from '@microsoft/msfs-sdk';
 import { FwsSoundManagerControlEvents } from 'systems-host/CpiomC/FlightWarningSystem/FwsSoundManager';
 
 type ModesType = {
@@ -64,7 +71,7 @@ export class LegacyGpws {
 
     this.Mode3MaxBaroAlt = NaN;
 
-    this.Mode4MaxRAAlt = NaN;
+    this.Mode4MaxRAAlt = 0;
 
     this.Mode2BoundaryLeaveAlt = NaN;
     this.Mode2NumTerrain = 0;
@@ -131,6 +138,21 @@ export class LegacyGpws {
     this.RetardState = createStateMachine(RetardStateMachine);
     this.RetardState.setState('landed');
   }
+  private isAirVsGroundMode = SimVar.GetSimVarValue('L:A32NX_GPWS_GROUND_STATE', 'Bool') !== 1;
+  private airborneFor5s = new NXLogicConfirmNode(5);
+  private airborneFor10s = new NXLogicConfirmNode(10);
+
+  private isApproachVsTakeoffState = SimVar.GetSimVarValue('L:A32NX_GPWS_APPROACH_STATE', 'Bool') === 1;
+
+  private isOverflightDetected = new NXLogicTriggeredMonostableNode(60, false);
+  // Only relevant if alternate mode 4b is enabled
+  private isMode4aInhibited = false;
+
+  // PIN PROGs
+  private isAudioDeclutterEnabled = false;
+  private isAlternateMode4bEnabled = false;
+  private isTerrainClearanceFloorEnabled = false;
+  private isTerrainAwarenessEnabled = false;
 
   gpwsUpdateDiscreteWords() {
     this.egpwsAlertDiscreteWord1.ssm = Arinc429SignStatusMatrix.NormalOperation;
@@ -226,20 +248,41 @@ export class LegacyGpws {
   gpws(deltaTime) {
     // EGPWS receives ADR1 only
     const baroAlt = Arinc429Word.fromSimVarValue('L:A32NX_ADIRS_ADR_1_BARO_CORRECTED_ALTITUDE_1');
+    const computedAirspeed = Arinc429Word.fromSimVarValue('L:A32NX_ADIRS_ADR_1_COMPUTED_AIRSPEED');
+    const pitch = Arinc429Word.fromSimVarValue('L:A32NX_ADIRS_IR_1_PITCH');
+    const inertialVs = Arinc429Word.fromSimVarValue('L:A32NX_ADIRS_IR_1_VERTICAL_SPEED');
+    const barometricVs = Arinc429Word.fromSimVarValue('L:A32NX_ADIRS_ADR_1_BAROMETRIC_VERTICAL_SPEED');
     const radioAlt1 = Arinc429Word.fromSimVarValue('L:A32NX_RA_1_RADIO_ALTITUDE');
     const radioAlt2 = Arinc429Word.fromSimVarValue('L:A32NX_RA_2_RADIO_ALTITUDE');
     const radioAlt = radioAlt1.isFailureWarning() || radioAlt1.isNoComputedData() ? radioAlt2 : radioAlt1;
     const radioAltValid = radioAlt.isNormalOperation();
-    const onGround = SimVar.GetSimVarValue('SIM ON GROUND', 'Bool');
+    const isOnGround = !this.isAirVsGroundMode;
+
+    const isGpwsSysOff = SimVar.GetSimVarValue('L:A32NX_GPWS_SYS_OFF', 'Bool') === 1;
+    const isTerrModeOff = SimVar.GetSimVarValue('L:A32NX_GPWS_TERR_OFF', 'Bool') === 1;
+    const isFlapModeOff = SimVar.GetSimVarValue('L:A32NX_GPWS_FLAP_OFF', 'Bool') === 1;
+    const isLdgFlap3On = SimVar.GetSimVarValue('L:A32NX_GPWS_FLAPS3', 'Bool') === 1;
+
+    const sfccPositionWord = Arinc429Word.fromSimVarValue('L:A32NX_SFCC_SLAT_FLAP_ACTUAL_POSITION_WORD');
+    const isFlapsFull = sfccPositionWord.bitValueOr(22, false);
+    const isFlaps3 = sfccPositionWord.bitValueOr(21, false) && !isFlapsFull;
+
+    const areFlapsInLandingConfig =
+      !sfccPositionWord.isNormalOperation() || isFlapModeOff || (isLdgFlap3On ? isFlaps3 : isFlapsFull);
+    const isGearDownLocked = SimVar.GetSimVarValue('L:A32NX_LGCIU_1_LEFT_GEAR_DOWNLOCKED', 'Bool') === 1;
+
+    // TODO only use this in the air?
+    const isNavAccuracyHigh = SimVar.GetSimVarValue('L:A32NX_FMGC_L_NAV_ACCURACY_HIGH', 'Bool') === 1;
+    const isTcfOperational = this.isTerrainClearanceFloorOperational(isTerrModeOff, radioAlt, isNavAccuracyHigh);
+    const isTafOperational = this.isTerrainAwarenessOperational(isTerrModeOff);
 
     this.UpdateAltState(radioAltValid ? radioAlt.value : NaN);
     this.differentiateRadioalt(radioAltValid ? radioAlt.value : NaN, deltaTime);
 
     const mda = SimVar.GetSimVarValue('L:AIRLINER_MINIMUM_DESCENT_ALTITUDE', 'feet');
     const dh = SimVar.GetSimVarValue('L:AIRLINER_DECISION_HEIGHT', 'feet');
-    const phase = SimVar.GetSimVarValue('L:A32NX_FMGC_FLIGHT_PHASE', 'Enum');
 
-    if (mda !== 0 || (dh !== -1 && dh !== -2 && phase === FmgcFlightPhase.Approach)) {
+    if (mda !== 0 || (dh !== -1 && dh !== -2 && this.isApproachVsTakeoffState)) {
       let minimumsDA; // MDA or DH
       let minimumsIA; // radio or baro altitude
       if (dh >= 0) {
@@ -254,34 +297,40 @@ export class LegacyGpws {
       }
     }
 
-    const tawsSelected: number = SimVar.GetSimVarValue('L:A32NX_WXR_TAWS_SYS_SELECTED', SimVarValueType.Number);
-    const gpwsFailed =
-      tawsSelected === 1 || tawsSelected === 2
-        ? SimVar.GetSimVarValue(`L:A32NX_GPWS_${tawsSelected}_FAILED`, 'Bool')
-        : true;
+    this.updateMaxRA(radioAlt, isOnGround);
 
-    if (
-      radioAltValid &&
-      radioAlt.value >= 10 &&
-      radioAlt.value <= 2450 &&
-      !SimVar.GetSimVarValue('L:A32NX_GPWS_SYS_OFF', 'Bool') &&
-      !gpwsFailed
-    ) {
-      // Activate between 10 - 2450 radio alt unless SYS is off
-      const flapsThreeSelected = SimVar.GetSimVarValue('L:A32NX_SPEEDS_LANDING_CONF3', 'Bool');
-      const FlapPosition = SimVar.GetSimVarValue('L:A32NX_FLAPS_HANDLE_INDEX', 'Number');
-      const FlapsInLandingConfig = flapsThreeSelected ? FlapPosition === 3 : FlapPosition === 4; // fixme should be actual flap angle
-      const vSpeed = Simplane.getVerticalSpeed();
-      const Airspeed = SimVar.GetSimVarValue('AIRSPEED INDICATED', 'Knots');
-      const gearExtended = SimVar.GetSimVarValue('GEAR TOTAL PCT EXTENDED', 'Percent') > 0.9;
+    const isOverflightDetected = this.updateOverflightState(deltaTime);
+    this.updateMode4aInhibited(isGearDownLocked, areFlapsInLandingConfig);
 
-      this.updateMaxRA(radioAlt.value, onGround, phase);
+    this.updateAirGroundState(deltaTime, computedAirspeed, radioAlt, pitch);
+    this.updateApproachTakeoffState(
+      computedAirspeed,
+      radioAlt,
+      isGearDownLocked,
+      areFlapsInLandingConfig,
+      isTcfOperational,
+      isTafOperational,
+      isOverflightDetected,
+    );
+
+    if (!isGpwsSysOff && radioAltValid && radioAlt.value >= 10 && radioAlt.value <= 2450) {
+      //Activate between 10 - 2450 radio alt unless SYS is off
+      const altRate = this.selectAltitudeRate(inertialVs, barometricVs);
 
-      this.GPWSMode1(this.modes[0], radioAlt.value, vSpeed);
+      this.GPWSMode1(this.modes[0], radioAlt.value, altRate);
       // Mode 2 is disabled because of an issue with the terrain height simvar which causes false warnings very frequently. See PR#1742 for more info
-      // this.GPWSMode2(this.modes[1], radioAlt, Airspeed, FlapsInLandingConfig, gearExtended);
-      this.GPWSMode3(this.modes[2], radioAlt.value, phase);
-      this.GPWSMode4(this.modes[3], radioAlt.value, Airspeed, FlapsInLandingConfig, gearExtended, phase);
+      //this.GPWSMode2(this.modes[1], radioAlt, computedAirspeed, areFlapsInLandingConfig, isGearDownLocked);
+      this.GPWSMode3(this.modes[2], baroAlt, radioAlt.value, altRate, areFlapsInLandingConfig, isGearDownLocked);
+      this.GPWSMode4(
+        this.modes[3],
+        radioAlt.value,
+        computedAirspeed,
+        areFlapsInLandingConfig,
+        isGearDownLocked,
+        isTcfOperational,
+        isTafOperational,
+        isOverflightDetected,
+      );
       this.GPWSMode5(this.modes[4], radioAlt.value);
     } else {
       this.modes.forEach((mode) => {
@@ -289,9 +338,6 @@ export class LegacyGpws {
       });
 
       this.Mode3MaxBaroAlt = NaN;
-      if (onGround || (radioAltValid && radioAlt.value < 10)) {
-        this.Mode4MaxRAAlt = NaN;
-      }
 
       this.setGlideSlopeWarning(false);
       this.setGpwsWarning(false);
@@ -319,12 +365,12 @@ export class LegacyGpws {
     }
   }
 
-  updateMaxRA(radioAlt, onGround, phase) {
+  updateMaxRA(radioAlt, isOnGround) {
     // on ground check is to get around the fact that radio alt is set to around 300 while loading
-    if (onGround || phase === FmgcFlightPhase.GoAround) {
-      this.Mode4MaxRAAlt = NaN;
-    } else if (this.Mode4MaxRAAlt < radioAlt || Number.isNaN(this.Mode4MaxRAAlt)) {
-      this.Mode4MaxRAAlt = radioAlt;
+    if (isOnGround || this.isApproachVsTakeoffState) {
+      this.Mode4MaxRAAlt = 0;
+    } else if (radioAlt.isNormalOperation()) {
+      this.Mode4MaxRAAlt = Math.max(this.Mode4MaxRAAlt, 0.75 * radioAlt.value);
     }
   }
 
@@ -391,12 +437,12 @@ export class LegacyGpws {
    * Compute the GPWS Mode 1 state.
    * @param mode - The mode object which stores the state.
    * @param radioAlt - Radio altitude in feet
-   * @param vSpeed - Vertical speed, in feet/min, should be inertial vertical speed, not sure if simconnect provides that
+   * @param vSpeed - Vertical speed, in feet/min, NaN if not available
    */
   GPWSMode1(mode, radioAlt, vSpeed) {
     const sinkrate = -vSpeed;
 
-    if (sinkrate <= 1000) {
+    if (!Number.isFinite(sinkrate) || sinkrate <= 1000) {
       mode.current = 0;
       return;
     }
@@ -417,23 +463,27 @@ export class LegacyGpws {
    * Compute the GPWS Mode 2 state.
    * @param mode - The mode object which stores the state.
    * @param radioAlt - Radio altitude in feet
-   * @param speed - Airspeed in knots.
-   * @param FlapsInLandingConfig - If flaps is in landing config
+   * @param computedAirspeed - Arinc429 value of the computed airspeed in knots.
+   * @param areFlapsInLandingConfig - If flaps is in landing config
    * @param gearExtended - If the gear is deployed
    */
-  GPWSMode2(mode, radioAlt, speed, FlapsInLandingConfig, gearExtended) {
+  GPWSMode2(mode, radioAlt, computedAirspeed, areFlapsInLandingConfig, gearExtended) {
+    if (!computedAirspeed.isNormalOperation()) {
+      return false;
+    }
+
     let IsInBoundary = false;
     const UpperBoundaryRate =
       -this.RadioAltRate < 3500 ? 0.7937 * -this.RadioAltRate - 1557.5 : 0.19166 * -this.RadioAltRate + 610;
-    const UpperBoundarySpeed = Math.max(1650, Math.min(2450, 8.8888 * speed - 305.555));
+    const UpperBoundarySpeed = Math.max(1650, Math.min(2450, 8.8888 * computedAirspeed.value - 305.555));
 
-    if (!FlapsInLandingConfig && -this.RadioAltRate > 2000) {
+    if (!areFlapsInLandingConfig && -this.RadioAltRate > 2000) {
       if (radioAlt < UpperBoundarySpeed && radioAlt < UpperBoundaryRate) {
         this.Mode2NumFramesInBoundary += 1;
       } else {
         this.Mode2NumFramesInBoundary = 0;
       }
-    } else if (FlapsInLandingConfig && -this.RadioAltRate > 2000) {
+    } else if (areFlapsInLandingConfig && -this.RadioAltRate > 2000) {
       if (radioAlt < 775 && radioAlt < UpperBoundaryRate && -this.RadioAltRate < 10000) {
         this.Mode2NumFramesInBoundary += 1;
       } else {
@@ -470,31 +520,33 @@ export class LegacyGpws {
 
   /**
    * Compute the GPWS Mode 3 state.
-   * @param mode - The mode object which stores the state.
-   * @param radioAlt - Radio altitude in feet
-   * @param phase - Flight phase index
-   * @param FlapsInLandingConfig - If flaps is in landing config
-   * @constructor
+   * @param {*} mode - The mode object which stores the state.
+   * @param {*} baroAlt - Arinc429 value of the barometric altitude in feet.
+   * @param {*} radioAlt - Radio altitude in feet
+   * @param {*} altRate - Altitude rate in feet per minute
+   * @param {*} areFlapsInLandingConfig - True if flaps is in landing config
+   * @param {*} isGearDownLocked - True if the gear is down and locked
    */
-  GPWSMode3(mode, radioAlt, phase) {
+  GPWSMode3(mode, baroAlt, radioAlt, altRate, areFlapsInLandingConfig, isGearDownLocked) {
     if (
-      !(phase === FmgcFlightPhase.Takeoff || phase === FmgcFlightPhase.GoAround) ||
+      (isGearDownLocked && areFlapsInLandingConfig) ||
+      this.isApproachVsTakeoffState ||
       radioAlt > 1500 ||
-      radioAlt < 10
+      radioAlt < 10 ||
+      !baroAlt.isNormalOperation()
     ) {
       this.Mode3MaxBaroAlt = NaN;
       mode.current = 0;
       return;
     }
 
-    const baroAlt = SimVar.GetSimVarValue('PLANE ALTITUDE', 'feet');
-
     const maxAltLoss = 0.09 * radioAlt + 7.1;
+    const hasPositiveAltRate = Number.isFinite(altRate) && altRate > 0;
 
-    if (baroAlt > this.Mode3MaxBaroAlt || Number.isNaN(this.Mode3MaxBaroAlt)) {
-      this.Mode3MaxBaroAlt = baroAlt;
+    if (baroAlt.value > this.Mode3MaxBaroAlt || Number.isNaN(this.Mode3MaxBaroAlt)) {
+      this.Mode3MaxBaroAlt = baroAlt.value;
       mode.current = 0;
-    } else if (this.Mode3MaxBaroAlt - baroAlt > maxAltLoss) {
+    } else if (!hasPositiveAltRate && this.Mode3MaxBaroAlt - baroAlt.value > maxAltLoss) {
       mode.current = 1;
     } else {
       mode.current = 0;
@@ -505,42 +557,70 @@ export class LegacyGpws {
    * Compute the GPWS Mode 4 state.
    * @param mode - The mode object which stores the state.
    * @param radioAlt - Radio altitude in feet
-   * @param speed - Airspeed in knots.
-   * @param FlapsInLandingConfig - If flaps is in landing config
+   * @param computedAirspeed - ARINC value of the computed airspeed in knots.
+   * @param areFlapsInLandingConfig - If flaps is in landing config
    * @param gearExtended - If the gear is extended
-   * @param phase - Flight phase index
+   * @param tcfOperational - If the terrain clearance floor is operational
+   * @param tafOperational - If the terrain awareness floor is operational
+   * @param isOverflightDetected - If an overflight is detected
    * @constructor
    */
-  GPWSMode4(mode, radioAlt, speed, FlapsInLandingConfig, gearExtended, phase) {
-    if (radioAlt < 30 || radioAlt > 1000) {
-      mode.current = 0;
+  GPWSMode4(
+    mode,
+    radioAlt,
+    computedAirspeed,
+    areFlapsInLandingConfig,
+    gearExtended,
+    tcfOperational,
+    tafOperational,
+    isOverflightDetected,
+  ) {
+    mode.current = 0;
+
+    if (!computedAirspeed.isNormalOperation() || radioAlt < 30 || radioAlt > 1000 || !this.isAirVsGroundMode) {
       return;
     }
-    const FlapModeOff = SimVar.GetSimVarValue('L:A32NX_GPWS_FLAP_OFF', 'Bool');
 
-    // Mode 4 A and B logic
-    if (!gearExtended && phase === FmgcFlightPhase.Approach) {
-      if (speed < 190 && radioAlt < 500) {
-        mode.current = 1;
-      } else if (speed >= 190) {
-        const maxWarnAlt = 8.333 * speed - 1083.333;
-        mode.current = radioAlt < maxWarnAlt ? 3 : 0;
+    const isMode4cEnabled =
+      !this.isApproachVsTakeoffState && (!areFlapsInLandingConfig || !gearExtended) && this.isAirVsGroundMode;
+
+    // Mode 4 A
+    if (this.isApproachVsTakeoffState && !gearExtended && !this.isMode4aInhibited) {
+      const boundary = this.mode4aUpperBoundary(
+        computedAirspeed.value,
+        areFlapsInLandingConfig,
+        tcfOperational,
+        tafOperational,
+        isOverflightDetected,
+      );
+
+      if (computedAirspeed.value < 190 && radioAlt < 500) {
+        mode.current = 1; // TOO LOW GEAR
+      } else if (computedAirspeed.value >= 190 && radioAlt < boundary) {
+        mode.current = areFlapsInLandingConfig ? 1 : 3; // TOO LOW GEAR or TOO LOW TERRAIN
       }
-    } else if (!FlapsInLandingConfig && !FlapModeOff && phase === FmgcFlightPhase.Approach) {
-      if (speed < 159 && radioAlt < 245) {
-        mode.current = 2;
-      } else if (speed >= 159) {
-        const maxWarnAlt = 8.2967 * speed - 1074.18;
-        mode.current = radioAlt < maxWarnAlt ? 3 : 0;
+      // Mode 4 B
+    } else if (this.isApproachVsTakeoffState && (!areFlapsInLandingConfig || !gearExtended)) {
+      // Normal 4b mode, flaps down, what is the boundary?
+      const boundary = this.mode4bUpperBoundary(
+        computedAirspeed.value,
+        areFlapsInLandingConfig,
+        tcfOperational,
+        tafOperational,
+        isOverflightDetected,
+      );
+
+      if (computedAirspeed.value < 159 && radioAlt < 245) {
+        mode.current = !gearExtended ? 1 : 2; // TOO LOW GEAR or TOO LOW FLAPS
+      } else if (computedAirspeed.value >= 159 && radioAlt < boundary) {
+        mode.current = this.isMode4aInhibited ? 1 : 3; // TOO LOW GEAR or TOO LOW TERRAIN
       }
-    } else {
-      mode.current = 0;
-    }
-    if (!FlapsInLandingConfig || !gearExtended) {
-      const maxWarnAltSpeed = Math.max(Math.min(8.3333 * speed - 1083.33, 1000), 500);
-      const maxWarnAlt = 0.750751 * this.Mode4MaxRAAlt - 0.750751;
+      // Mode 4 C
+    } else if (isMode4cEnabled) {
+      const maximumFloor = this.mode4cUpperBoundary(computedAirspeed.value);
+      const maximumFilterValue = Math.min(maximumFloor, this.Mode4MaxRAAlt);
 
-      if (this.Mode4MaxRAAlt > 100 && radioAlt < maxWarnAltSpeed && radioAlt < maxWarnAlt) {
+      if (radioAlt < maximumFilterValue) {
         mode.current = 3;
       }
     }
@@ -808,6 +888,151 @@ export class LegacyGpws {
         break;
     }
   }
+  updateAirGroundState(deltaTime, computedAirspeed, radioAlt, pitchAngle) {
+    if (!computedAirspeed.isNormalOperation() || !radioAlt.isNormalOperation()) {
+      // Stay in current state
+      return;
+    }
+
+    this.airborneFor5s.write(
+      computedAirspeed.value > 90 && radioAlt.value > 25 && pitchAngle.isNormalOperation() && pitchAngle.value > 5,
+      deltaTime,
+    );
+    this.airborneFor10s.write(computedAirspeed.value > 90 && radioAlt.value > 25, deltaTime);
+
+    if (this.isAirVsGroundMode) {
+      if (radioAlt.value < 25) {
+        this.isAirVsGroundMode = false;
+        SimVar.SetSimVarValue('L:A32NX_GPWS_GROUND_STATE', 'Bool', 1);
+      }
+    } else {
+      if (this.airborneFor5s.read() || this.airborneFor5s.read()) {
+        this.isAirVsGroundMode = true;
+        SimVar.SetSimVarValue('L:A32NX_GPWS_GROUND_STATE', 'Bool', 0);
+      }
+    }
+  }
+
+  updateApproachTakeoffState(
+    computedAirspeed,
+    radioAlt,
+    isGearDown,
+    areFlapsInLandingConfig,
+    tcfOperational,
+    tafOperational,
+    isOverflightDetected,
+  ) {
+    // TODO: what do we do if computedAirspeed is not NO?
+    if (!computedAirspeed.isNormalOperation()) {
+      return;
+    }
+
+    if (this.isApproachVsTakeoffState) {
+      // Switch to TO if we pass below 245 ft mode 4b floor without an alert (i.e gear down and flaps in landing config)
+      if (radioAlt.isNormalOperation() && radioAlt.value < 245 && isGearDown && areFlapsInLandingConfig) {
+        this.isApproachVsTakeoffState = false;
+        SimVar.SetSimVarValue('L:A32NX_GPWS_APPROACH_STATE', 'Bool', 0);
+      }
+    } else {
+      const isFirstAlgorithmSatisfied = false;
+      // - 4C filter value exceeds 4A alert boundary
+      const isSecondAlgorithmSatisfied =
+        this.Mode4MaxRAAlt >
+        this.mode4aUpperBoundary(
+          computedAirspeed.value,
+          areFlapsInLandingConfig,
+          tcfOperational,
+          tafOperational,
+          isOverflightDetected,
+        );
+
+      if ((isFirstAlgorithmSatisfied || !this.isAudioDeclutterEnabled) && isSecondAlgorithmSatisfied) {
+        this.isApproachVsTakeoffState = true;
+        SimVar.SetSimVarValue('L:A32NX_GPWS_APPROACH_STATE', 'Bool', 1);
+      }
+    }
+  }
+
+  mode4aUpperBoundary(computedAirspeed, areFlapsInLandingConfig, tcfOperational, tafOperational, isOverflightDetected) {
+    let expandedBoundary = 1000;
+    if (areFlapsInLandingConfig || tcfOperational || tafOperational) {
+      expandedBoundary = 500;
+    } else if (isOverflightDetected) {
+      expandedBoundary = 800;
+    }
+
+    return Math.max(500, Math.min(expandedBoundary, 8.333 * computedAirspeed - 1083.33));
+  }
+
+  mode4bUpperBoundary(computedAirspeed, areFlapsInLandingConfig, tcfOperational, tafOperational, isOverflightDetected) {
+    let expandedBoundary = 1000;
+    if (areFlapsInLandingConfig || tcfOperational || tafOperational) {
+      expandedBoundary = 245;
+    } else if (isOverflightDetected) {
+      expandedBoundary = 800;
+    }
+
+    return Math.max(245, Math.min(expandedBoundary, 8.333 * computedAirspeed - 1083.33));
+  }
+
+  mode4cUpperBoundary(computedAirspeed) {
+    return Math.max(500, Math.min(1000, 8.3333 * computedAirspeed.value - 1083.33));
+  }
+
+  updateOverflightState(deltaTime) {
+    // Need -2200 ft/s to trigger an overflight state
+    return this.isOverflightDetected.write(this.RadioAltRate < -2200 * 60, deltaTime);
+  }
+
+  isTerrainClearanceFloorOperational(terrPbOff, radioAlt, fmcNavAccuracyHigh) {
+    // TODO when ground speed is below 60 kts, always consider fms nav accuracy high
+    // where does GS come from?
+    return this.isTerrainAwarenessEnabled && !terrPbOff && radioAlt.isNormalOperation() && fmcNavAccuracyHigh;
+  }
+
+  isTerrainAwarenessOperational(terrPbOff) {
+    // TODO replace placeholders
+    const doesTerrainAwarenessUseGeometricAltitude = true;
+    const isGeometricAltitudeVfomValid = true;
+    const isGeometricAltitudeHilValid = true;
+    const geometricAltitudeVfom = 0;
+    const isRaimFailureDetected = false;
+
+    return (
+      this.isTerrainAwarenessEnabled &&
+      !terrPbOff &&
+      !doesTerrainAwarenessUseGeometricAltitude &&
+      isGeometricAltitudeVfomValid &&
+      isGeometricAltitudeHilValid &&
+      !isRaimFailureDetected &&
+      geometricAltitudeVfom < 200
+    );
+  }
+
+  updateMode4aInhibited(isGearDownLocked, isFlapsInLandingConfig) {
+    if (this.isMode4aInhibited) {
+      if (!this.isAirVsGroundMode || !this.isApproachVsTakeoffState) {
+        // Reset
+        this.isMode4aInhibited = false;
+      }
+    } else if (this.isAlternateMode4bEnabled) {
+      if (isGearDownLocked || isFlapsInLandingConfig) {
+        this.isMode4aInhibited = true;
+      }
+    }
+  }
+
+  selectAltitudeRate(inertialVs, baroVs) {
+    if (inertialVs.isNormalOperation()) {
+      return inertialVs.value;
+    } else if (Number.isFinite(this.RadioAltRate)) {
+      return this.RadioAltRate;
+    } else if (baroVs.isNormalOperation()) {
+      return baroVs.value;
+    }
+
+    return NaN;
+  }
 }
 
 const RetardStateMachine = {