Overview

The AFS parameter group configures the Advanced Failsafe library. This subsystem is distinct from the standard FS_ (Failsafe) parameters found in Plane/Copter. It is designed to meet strict Flight Termination System (FTS) requirements for regulatory compliance or competitions (e.g., UAV Challenge Outback Rescue).

Unlike standard failsafes which try to save the vehicle (RTL, Land), AFS is often designed to "Terminate" the flight to ensure safety of people on the ground if the vehicle goes rogue.

Key Concepts

1. Flight Termination (AFS_TERMINATE)

The core function of AFS. If a critical failure condition is met (RC Loss, GCS Loss, Geofence Breach), the system can be configured to:

• Kill Motors: Immediately stop propulsion.
• Move Servos: Force control surfaces to a "Crash" or "Spin" position (e.g., full rudder, full up elevator) to limit the impact area.
• Hardware Pin: Drive a GPIO pin (AFS_TERM_PIN) high/low to trigger an external parachute deployment module or airbag.

2. Dual-Link Monitoring

AFS can monitor both the RC link and the GCS (MAVLink) link independently (AFS_DUAL_LOSS). It ensures that you always have at least one valid command link.

3. Heartbeat Hardware (AFS_HB_PIN)

Can output a "heartbeat" signal to an external watchdog timer. If the autopilot freezes, the heartbeat stops, and the external hardware terminates the flight.

Parameter Breakdown

• AFS_ENABLE: Master switch.
• AFS_TERM_ACTION: 0=Disable, 1=Terminate immediately on failure.
• AFS_MAN_PIN: Input pin for a manual "Kill Switch" from an external receiver.
• AFS_TERM_PIN: Output pin to trigger external termination hardware.
• AFS_RC_FAIL_TIME: Timeout (seconds) for RC loss before termination.
• AFS_AMSL_LIMIT: Hard altitude ceiling (AMSL) for termination.

Integration Guide

Typical Setup for FTS

1. Enable: Set AFS_ENABLE = 1.
2. Define Output: Set AFS_TERM_PIN to the Servo/GPIO connected to your parachute release or ignition kill.
3. Define Logic: Configure AFS_RC_FAIL_TIME and AFS_GCS_TIMEOUT appropriately.
4. Testing: REMOVE PROPELLERS. Use the AFS.TERMINATE MAVLink command or simulate a link loss to verify the pin switches state.

Developer Notes

• Library: libraries/AP_AdvancedFailsafe
• Vehicle: Primarily used in ArduPlane.
• Warning: Misconfiguring this WILL crash your plane. This is a "destruct" system, not a "save me" system.