fw pos ctrl: use hardcoded buffer altitude instead of parameter for clearance altitude buffer

src/modules/fw_pos_control_l1/FixedwingPositionControl.cpp

@@ -1373,7 +1373,7 @@ FixedwingPositionControl::control_auto_takeoff(const hrt_abstime &now, const flo
 
 	// set the altitude to something above the clearance altitude to ensure the vehicle climbs past the value
 	// (navigator will accept the takeoff as complete once crossing the clearance altitude)
-	const float altitude_setpoint_amsl = clearance_altitude_amsl + _param_nav_fw_alt_rad.get();
+	const float altitude_setpoint_amsl = clearance_altitude_amsl + kClearanceAltitudeBuffer;
 
 	Vector2f local_2D_position{_local_pos.x, _local_pos.y};
 

src/modules/fw_pos_control_l1/FixedwingPositionControl.hpp

@@ -148,6 +148,10 @@ static constexpr float AIR_DENSITY_STANDARD_ATMOS_5000_AMSL = 0.7363f;
 // [rad] minimum pitch while airspeed has not yet reached a controllable value in manual position controlled takeoff modes
 static constexpr float MIN_PITCH_DURING_MANUAL_TAKEOFF = 0.0f;
 
+// [m] arbitrary buffer altitude added to clearance altitude setpoint during takeoff to ensure aircraft passes the clearance
+// altitude while waiting for navigator to flag it exceeded
+static constexpr float kClearanceAltitudeBuffer = 10.0f;
+
 class FixedwingPositionControl final : public ModuleBase<FixedwingPositionControl>, public ModuleParams,
 	public px4::WorkItem
 {