Low-tech ways to down a low-flying plane on a known flightpass abound.
I would use a cluster of home-made 12 inch or bigger mortar tubes lobbing explosive-filled gas-tanks with propellant amount and fuse-length measured to achieve detonation next to the plane.
Alternatively a few dosen pounds of nails can be shot from each tube in a hope to get a few into the engines.
How about suddenly releasing a line of helium baloons tethered to something heavy by 2000-feet steel cables?
All such technologies made from materials commonly available in USA can be safely tested and calibrated even in low-populated areas of USA, let alone in some other country with exact specifications and ballistic settings tables passed here for manufacture.
P.S. Of course if I have a 12 inch tube and an explosive-filled gas-tank, why would I try to shoot a plane in the air - there are plenty of them right on the tarmack or other targets for that matter.
miko