Just in response to Centauus, what you are suggesting is exactly what we do here in the United Arab Emirates. If anyone has a faulty Transponder,eg. not squawking mode C, or incorrect altitude, for inbounds not already in UAE airspace they are not allowed to enter. If already in the airspace they land and are then grounded indefinately till the problem is fixed, and checked and only then are they allowed to fly again. Then again we don't have E airspace so above 4,500ft is all C and A airspace with everyone identified and separated. But just like I would never compare the US airspace with Australias airspace, I wouldn't compare middle eastern airspace with Oz airspace either. Every airspace has its own specific needs.