Helicopters (used for media coverage, passenger transport and medical emergency) provide the perfect template for the Aviation Authority and Amazon to base a framework of operation on.

The main considerations will be:

- Set routes/paths the drones must follow, taking I to account altitudes that minimise traffic with other things high up (buildings, aircraft, UFOs) - emergency procedures and a risk assessment for each foreseeable eventuality (not that hard considering the lack of other traffic 'up there') - limits on the amount of drones in the air within constrained geographic localities.

It is likely that this could all be agreed for a single trial city well before 2015 rolls around. This isn't rocket science...

I don't know about America but in the UK aviation authorities already permit flying models [1] and aerial work such as photography if certain requirements are met [2]. Regulators are understandably keen on collision avoidance, so they usually say UAVs must stay within the operator's line of sight - or have a 'sense and avoid' system. The UK's CAA "is not currently aware of any Sense-and-Avoid system with adequate performance and reliability" [3]

So, that's the regulatory challenge. Need to sense and avoid obstacles and other aircraft, and do a good enough job of it that aviation authorities will sign off on it.

(In addition to the regulatory challenge, there may also be business, operational and engineering challenges.)

[1] http://www.caa.co.uk/default.aspx?catid=1416&pageid=8153 [2] http://www.caa.co.uk/default.aspx?catid=1995&pageid=11213 [3] http://www.caa.co.uk/default.aspx?catid=1995&pageid=11186