Concentrate all of the damage at one airfield so that planes with reduced fuel could not land
That's possible, but I couldn't cover all scenarios. One might have been that they would clog up multiple airport runways, thus diverting more and more planes to more and more airports, with the intent of clogging up as much as possible and creating an impossible situation for the air controllers. They may have created so much fear that airplanes may have run out of fuel or may have been forced to ditch, thus dramatically driving up casualties. One thing I didn't take into account was that it would have been quickly learned that all the planes were coming from one airport in England, thus any flights from there would have been the most suspect, and they would have been diverted to more isolated runways if possible.