We've had a couple of incidents in the UK recently that demonstrated the 'lag' in interception of non-communicative aircraft.

In April 2016 a German-registered Challenger business jet flew east-west across the UK and was just about to enter Irish airspace when the RAF Typhoons reached it.

Then in October the same happened with a Volaris A320 that managed to fly most of the south-north extent of the UK before being intercepted, again just before leaving UK airspace.

In both cases if there had been any malicious intent then it could easily have been executed over major cities. In fact I watched that A320 fly over my town... The problem in the UK is that the main fighter bases are on the east coast, to combat the Soviet hordes that never arrived. So basically everything is a supersonic tail-chase for the interceptors unless it's coming from the Benelux countries. The RAF really needs to redispose its units for dealing with the new 'threat' but there's simply no money to do so.

There are vary levels of readiness, from pilots sitting in the jet with the engines turned on, to pilots sitting equipped 2 minute away from the plane, and so on.

And it looks like the 2 planes came from different bases.

It depends on the level of altertness an "Alarmrotte" has. That can range from 5 to 15 minutes from "beeing on the ground" to "flying to destination".

If you look at this map of German airforce bases, one of the biggest is in Cologne (Köln-Wahn), so its no surprise that they were this quick

http://www.luftwaffe.de/portal/a/luftwaffe/start/team/stan/!...

Interesting that they intercepted after only 15 minutes. Maybe the aircraft had crossed the border without making contact. In the US, airliners accidentally lose contact for close to this time period quite frequently. To reestablish, the controllers will sometimes have a fellow company ship relay a message with the correct frequency via ACARS, or the lost aircraft can listen on 121.5 until someone calls with the correct frequency. I suppose in Europe this would be considered a more critical issue due to the frequent border crossings.

It's dependant on the airspace you are flying through and when are you supposed to make contact.

Try flying over NYC out of contact for 15min and lets see how it goes.

An airliner at that altitude would be well outside of any city's airspace.

I know, there are still different communication requirements for different airspaces.

When you file your travel plans you'll have to check in with different ATCs at different points, you are also likely to be contacted by ATCs depending on the flight plan, conditions and various other factors during the flight.

If you do not check in on schedule e.g. when there is a handover of ATCs or you do not respond to ATCs that trying to make contact with you, there will be a flag and an alert will be likely sent. If this goes on for minutes then they'll assume something was wrong and follow their procedure to make contact and investigate which might involve scrambling jets to make visual contact.

It's not like pilots can be too busy to respond to ATCs yes they might delay a response if they are in a middle of a sentence with a member of the air crew but that's a 5 seconds delay. Even a 1 minute delay would be flagged and you'll likely to be asked why you haven't responded or made contact on time.