Thrust loss: full throttle and still descending (ERR THRUST_LOSS_CHECK-1)

What ArduPilot says:

• ERR THRUST_LOSS_CHECK (Subsys 25)

For 1 s the copter was close to level (asked to lean less than 15°), with the throttle above 90% or the motors at their upper limit, holding its attitude within 30°, and still going down. ArduPilot takes it for a lost or too weak motor: “Potential Thrust Loss (n)” names the motor asked for the most thrust. On frames with six or more motors the others are then allowed full thrust, at the cost of yaw control, to keep the copter level; on a quadcopter nothing can make up for a lost motor. Land at once.

What to do, most likely first

1. A motor stopped, an ESC cut out, or a prop broke or came off.

   CheckIn the log that motor's output in RCOU is at maximum while the others are lower; ESC telemetry, if present, shows its RPM or current at zero.

   FixInspect the named motor's arm: prop, nut, motor, ESC, connectors and solder joints.

2. The aircraft is too heavy for its motors, or the battery sagged so far that full throttle no longer lifts it.

   CheckAll the outputs in RCOU are near maximum together, and the battery voltage is low.

   FixReduce the weight or fit a power train with more thrust: hovering should need about half throttle. Land before the battery is nearly empty.

Parameters to look at

Where to do it:Failsafe ExplainerSetup & Tuning Guide