MAV_RESULT 2 (2) — DENIED — command permanently denied

The command was understood and is supported, but the vehicle refuses it in its current state. Retrying without changing state will not help.

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Diagnosis

When you hit this

Arming while a pre-arm check is failing, which is by far the most common case.
Commanding a mode change the vehicle cannot enter, such as a GPS mode without a fix.
Requesting takeoff without the vehicle being armed.

Resolution

How to fix it

Read the STATUSTEXT messages
The vehicle almost always explains a denial in STATUSTEXT. That message names the failing pre-arm check; the MAV_RESULT alone does not.
Fix the state, do not retry
DENIED is deterministic. Resolve the pre-arm condition first.
Check mode prerequisites
Position-holding modes need a position estimate. Without one, the mode change is denied rather than failed.

Normalization

What Forge does about it

This code is reported by the device itself, so it survives normalization as data. Forge maps the vendor's fault register into the canonical fields alarm_code and alarm_description (and alarm_severity where the vendor supplies one), so an agent reads the same three fields whether the fault came from a Haas, a SINUMERIK, or a Cat engine. Forge does not clear the fault — that is the controller's job.