Also, if you are shooting large airliners, it'll be almost 100% fine with them, but as for private planes, or planes owned by small organizations, do yourself a big favor (and also for them) by asking for permission before you shoot away.
I have great shots of an Adventist Aviation Papua PC-6 and Tariku Caravans operating off jungle strips, but they prefer not to get their shots published (The operators are missionary and humanitarian, respectively.)
As FlyingPhotog has already pointed out, be very, very careful on the ramp (airplane parking lots). Especially in Papua, we have at least one incident per year which involves a careless pilot and an unsuspecting catering truck driver. (Or the opposite - a careless driver) My airport is infamous for having local residents randomly playing on the runway, so the control tower has a siren that it turns on 5 minutes prior to airplane action. Well, one day I was standing about 7 feet from the runway when they gave me the siren warning - I turned around to see a big fat Antonov 12 on final. I pretty much ran away from the runway for my life.
(But I still got my shot.)
Anyway, be careful, don't act like a terrorist, obey authorities, and so on. Your Sigma 120-400 will serve you well.