The mission lacks an item that is required for arming

What ArduPilot says:

• PreArm: Missing mission item: …

ARMING_MIS_ITEMS lists kinds of mission item that must be in the stored mission before arming is allowed: bit 0 a landing, bit 1 a VTOL landing, bit 2 DO_LAND_START, bit 3 a take-off, bit 4 a VTOL take-off, bit 5 a rally point, bit 6 RTL. The message names the first kind it did not find: land, vtol land, do land start, takeoff, vtol takeoff or RTL. The check looks only for an item of that kind anywhere in the mission, not at whether the mission makes sense. The default is 0: nothing is required.

What to do, most likely first

1. No mission is on the aircraft, or not the one you think.

   CheckRead the mission back from the aircraft in the ground station's Plan screen. MIS_TOTAL is the number of stored items; 0 or 1 means there is no mission.

   FixWrite the mission to the aircraft and read it back.

2. The mission has no such item: for example it stops at the last waypoint, with no landing and no RTL.

   FixAdd the item the message names and write the mission again.

3. The mission is erased at every start-up, because MIS_OPTIONS bit 0 is set.

   Check“Clearing Mission” is among the start-up messages.

   FixUpload the mission after every power-on, or clear bit 0 of MIS_OPTIONS so that the mission is kept.

4. ARMING_MIS_ITEMS came with another aircraft's parameters and asks for items this one cannot fly, such as a VTOL landing on an ordinary copter.

   CheckRead the bits of ARMING_MIS_ITEMS against the list above.

   FixKeep only the bits for items that your own missions must always contain.

Parameters to look at

Where to do it:Mission Energy CheckSetup & Tuning Guide