The disarm switch is in its “disarm” position

What ArduPilot says:

• PreArm: Disarm Switch on

A transmitter switch has the function Disarm (RCn_OPTION 81), and it is in its high position. While it is there ArduPilot refuses to arm by any means: a switch that says “disarm” and an armed aircraft cannot both be true.

What to do, most likely first

1. The switch was left high after the last disarm.

   FixMove it to its low position, then arm.

2. The channel is reversed or mixed in the transmitter, so “low” on the handle is “high” on the channel.

   CheckWatch that channel's bar in the Radio Calibration screen while you flip the switch: above 1800 µs is high.

   FixCorrect the channel's direction in the transmitter.

Parameters to look at

Where to do it:Setup & Tuning Guide