Fixed-wing autoland: Remove the dynamic altitude acceptance calculation and just use a simple separate landing altitude acceptance radius instead. This gives users that do not use LOITER-TO-ALT waypoints more control over their landing procedure

src/modules/navigator/navigator.h

@@ -345,6 +345,8 @@ private:
 		(ParamFloat<px4::params::NAV_ACC_RAD>) _param_acceptance_radius,	/**< acceptance for takeoff */
 		(ParamFloat<px4::params::NAV_FW_ALT_RAD>)
 		_param_fw_alt_acceptance_radius,	/**< acceptance radius for fixedwing altitude */
+		(ParamFloat<px4::params::NAV_FW_ALTL_RAD>)
+		_param_fw_alt_lnd_acceptance_radius,	/**< acceptance radius for fixedwing altitude before landing*/
 		(ParamFloat<px4::params::NAV_MC_ALT_RAD>)
 		_param_mc_alt_acceptance_radius,	/**< acceptance radius for multicopter altitude */
 		(ParamInt<px4::params::NAV_FORCE_VT>) _param_force_vtol,	/**< acceptance radius for multicopter altitude */

src/modules/navigator/navigator_main.cpp

@@ -868,15 +868,11 @@ float
 Navigator::get_altitude_acceptance_radius()
 {
 	if (!get_vstatus()->is_rotary_wing) {
-		// The fixed-wing altitude acceptance radius default is the respective parameter. However, before a landing
-		// approach it needs to be tighter: Assume a 30% error w.r.t. the remaining descent altitude is OK, but enforce
-		// min/max values (e.g. min=3m to make sure that the waypoint can still be reached in case of wrong user input).
-
 		const position_setpoint_s &next_sp = get_position_setpoint_triplet()->next;
-		const position_setpoint_s &curr_sp = get_position_setpoint_triplet()->current;
 
 		if (next_sp.type == position_setpoint_s::SETPOINT_TYPE_LAND && next_sp.valid) {
-			return math::constrain(0.3f * (curr_sp.alt - next_sp.alt), 3.0f, _param_fw_alt_acceptance_radius.get());
+			// Use separate (tighter) altitude acceptance for clean altitude starting point before landing
+			return _param_fw_alt_lnd_acceptance_radius.get();
 		}
 	}
 

src/modules/navigator/navigator_params.c

@@ -83,6 +83,20 @@ PARAM_DEFINE_FLOAT(NAV_ACC_RAD, 10.0f);
  */
 PARAM_DEFINE_FLOAT(NAV_FW_ALT_RAD, 10.0f);
 
+/**
+ * FW Altitude Acceptance Radius before a landing
+ *
+ * Altitude acceptance used for the last waypoint before a fixed-wing landing. This is usually smaller
+ * than the standard vertical acceptance because close to the ground higher accuracy is required.
+ *
+ * @unit m
+ * @min 0.05
+ * @max 200.0
+ * @decimal 1
+ * @group Mission
+ */
+PARAM_DEFINE_FLOAT(NAV_FW_ALTL_RAD, 5.0f);
+
 /**
  * MC Altitude Acceptance Radius
  *