Common Problems and Solutions

Fixes for common UAVLAS precision landing problems: no MAVLink message, intermittent or inaccurate position, circular motions and imprecise landing.

ULSDC-PBTS161026 · version 1.0.0 · issued October 16, 2026
The numbered PDF is the controlled copy: download it from the portal.

Introduction

Purpose

This guide lists the problems most often met when integrating and flying UAVLAS precision landing systems, with their likely causes and fixes.

Intended Audience

Integrators, operators and support engineers.

Applicability

This document applies to every UAVLAS precision landing system that connects to the autopilot over MAVLink: ULS-XCopter, ULS-ProCopter, ULS-Heli and ULS-XSpot. Product-specific installation, pinouts and wiring are in each product’s Operation Manual and Interface Control Document.

Troubleshooting

Before You Start

Most problems are solved by bringing everything up to date and repeating the setup:

  • Use the latest version of ULS-Tools.
  • Update the firmware of the transmitter and all receivers.
  • Use the latest ArduPilot or PX4 firmware.
  • Check the receiver and transmitter LED indications against the Operation Manual of your product.

Symptom: the autopilot receives no LANDING_TARGET message from the receiver.

  • Check that the transmitter is switched on and the receiver is in its field of view, with a clear line of sight.
  • Check the receiver power and the wiring of power, RX and TX (see the pinout and wiring diagram in the product’s Interface Control Document).
  • Check that the serial port baud rate and protocol on the autopilot match the receiver configuration (MAVLink 2).
  • On ArduPilot, check that the EXTRA1 (attitude) stream is enabled for the receiver’s serial port.
  • Check the receiver frame configuration: MAV_FRAME_BODY_FRD for ArduPilot, MAV_FRAME_LOCAL_NED for PX4.
  • Check the transmitter power supply.
  • When testing with QGroundControl, connect over telemetry, not USB: LANDING_TARGET may not be shown over a USB connection.

Intermittent Position Data

Symptom: position data drops in and out.

  • Keep the approach corridor and the line of sight between transmitter and receiver clear.
  • Re-orient the receiver(s) or the transmitter so the receiver stays inside the transmitter’s field of view.
  • Reduce the operating distance if you are close to the product’s maximum range.
  • Clean the receiver lens and the transmitter emission window.
  • Secure the receiver mounting to reduce vibration.

Inaccurate Position or Offset

Symptom: the reported position shows a large or constant offset from the real one.

  • Check that the receiver is mounted in the correct orientation and the mounting offset is set in the receiver configuration.
  • Check that the transmitter is level and its compass/IMU is calibrated.
  • Check for magnetic interference near the transmitter.
  • Indoors, reflections can disturb the measurement; test outdoors or in a controlled environment.
  • Check that precision loiter is set up on the autopilot (a switch assigned to PrecLoiter on ArduPilot), and that PLND_ENABLED and PLND_TYPE are set.

Circular Motions During Landing

  • Check the compass calibration of the ground unit (transmitter).
  • Check the compass calibration of the autopilot.
  • Check for magnetic interference on the ground.
  • Use compass override mode to debug the landing.
  • Check the precision landing PID settings.

The Landing Is Not Precise Enough

  • Check the position control PID settings of the autopilot.
  • On ArduPilot, check the Kalman filter settings of the PLND section.
  • Check the filter smoothness parameter on the receiver.
  • Check the trajectory jerk settings on the autopilot.

Transmitter or Receiver Not Powering

  • Check that the supply voltage is within the range given in the product’s datasheet.
  • Check the cables, connectors and the aircraft power rail.

If Nothing Works

Update the firmware of all UAVLAS devices, reset them to default settings and repeat the setup. Update the autopilot firmware, reset the autopilot parameters to default, and perform the autopilot calibrations and settings from the beginning. If the problem persists, contact UAVLAS support at https://uavlas.com/contact/ with your product, firmware versions and a flight log.