Just downloaded said app from an ad placed on YouTube. One word, wow. It's basically like Flightradar24 but from NATS. Great 3D and if you select Heathrow on the map and look at all the inbound flights, you can see a live image of the holding stacks and all the 'traces' (is that correct terminology?) of planes still visible to NATS. Impressive and free. That will kill the time on my next delay in Heathrow.