A stick is off-centre at the moment of arming

What ArduPilot says:

• PreArm: … (RCN) is not neutral

When you ask it to arm, roll, pitch and yaw must read exactly zero, which means within the dead zone (RCn_DZ, in µs) around the channel's trim (RCn_TRIM). With RC_OPTIONS bit 5 set (the default) the throttle must be at zero too. The message names the stick and its channel. Arming with the yaw stick does not count the yaw stick itself.

What to do, most likely first

1. The transmitter's trim buttons were moved after the calibration.

   CheckWith the sticks released, the named channel in the Radio Calibration screen should read its RCn_TRIM value, give or take the dead zone.

   FixCentre the transmitter's trims and leave them there: ArduPilot levels the aircraft itself. Calibrate the radio again if the centre still differs.

2. You were holding the stick while arming from a switch or the ground station.

   FixRelease roll, pitch and yaw, throttle fully down, then arm.

3. A worn or noisy stick does not come back to the same centre.

   CheckRelease the stick several times and watch the value: if it settles more than the dead zone away from the trim, this is it.

   FixRaise that channel's RCn_DZ a little (30 to 40 µs); a much larger dead zone makes the stick feel numb around the centre.

Parameters to look at

Where to do it:Setup & Tuning Guide