[Bug] Fixed-wing UAV not detecting landing in PX4 1.15.0 when GPS fusion is disabled

[heeveG]

Describe the bug

In PX4 stable release 1.15.0, there is an issue with fixed-wing UAVs (tested on a Holybro Pixhawk 6x). When GPS fusion is disabled, the UAV does not properly detect the landing state after entering flight state. The sequence is as follows:

• The UAV enters the “Flying” state correctly when arming and blowing into the airspeed sensor. • However, after simulated flight (blowing air into the airspeed sensor), when the airflow stops, the UAV often remains stuck in the “Flying” state. • Occasionally, it detects landing and disarms, but this is inconsistent. • When GPS lock is obtained, the problem is resolved. • This issue does not occur in PX4 firmware version 1.14.x, suggesting that it may be due to a change in EKF2 estimation in version 1.15.0. • The airspeed readings are below 6 when not blowing into the sensor, ruling out sensor misreading as the cause.

The issue seems to have appeared after the transition from PX4 version 1.14.x to 1.15.0. It appears to be related to EKF2 or other internal estimation processes when GPS fusion is disabled. No issues with the airspeed sensor were detected, as values are within expected limits. I’m seeking clarification on whether any EKF2 changes were made in version 1.15.0 that could be causing this behavior and advice on further debugging steps.

To Reproduce

1. Power on Holybro Pixhawk 6x fixed-wing UAV.
2. Disable GPS fusion.
3. Arm the UAV.
4. Simulate flight by blowing air into the airspeed sensor.
5. Stop airflow into the sensor.
6. Observe that the UAV remains in the “Flying” state rather than detecting landing.

Expected behavior

The UAV should exit the “Flying” state and detect landing after the airflow stops (i.e., when the airspeed is low) and disarm.

Screenshot / Media

(No media provided)

Flight Log

No response

Software Version

PX4 v1.15.0 (Stable)

Flight controller

Holybro Pixhawk 6x

Vehicle type

Fixed Wing

How are the different components wired up (including port information)

All components are wired per standard Holybro Pixhawk 6x setup for fixed-wing UAV.

Additional context

•	LNDFW_AIRSPD_MAX: default (6.00 m/s)
•	LNDFW_TRIG_TIME: default (2. s)
•	LNDFW_VEL_XY_MAX: default (5.0 m/s)
•	LNDFW_VEL_Z_MAX: default (1.0 m/s)
•	LNDFW_XYACC_MAX: default (8.0 m/s^2)