You want to help out your team and join a mission, but the planes are dogs-
Heres what you do to select your own aircraft and still be "in" the mission.
(1) Select mission, and click on any plane in mission
(2) Click accept
(3) Find out from mission boss what airfield mission is leaving from
(4) Click on hangar, select an aircraft which you would like to fly
(5) Bring up clipboard, click on base mission is leaving from
(6) Click "fly" before mission starts
You are now flying the aircraft you want, and also have access to mission channel and mission vox.