This answer helped me also, except that I am working with airplanes in stead of helicopters.
Aircraft setfuel 0 can also be used to prevent aircraft from taking off after they have landed via the aircraft land "land" command line.
Commandstop, aircraft disableAI "move", aircraft stop true, etc. doesn't work for this, the aircraft just keeps taking off.
Good job.
Cheerio,
Ronald Speirs