I don't think Howard has a private plan and here is why. He leased a plane to go to Bubba's wedding. He shared a plane with Ashton and Demi to fly back from Cali. There was that story that Beth had to drive instead of fly back from where ever she was due to bad weather. AND the kicker, Robin flies commercial. If Howard owned part or all of a plane isn't it reasonable to assume that she would also use it?