diydrones/ardupilot — pull request #1339 by priseborough (2014-08-25 07:24:51+00:00)
Title: AP_NavEKF : Clear compass fail on transition between armed and disarmed

This allows a compass that has been declared failed, possibly because of
external disturbances (eg movement of hatches, proximity of tools, etc)
to be given a second chance when the vehicle is armed.