Just to clarify that ATC considers it Mayday when 50%+ power has been lost. Its not that we aren't overly concerned by a 747 using only 3, there is always that 'if one's gone, so could the rest' so priority will still be given, but its not exactly going to affect a safe landing somewhere suitable, so a Pan is more appropriate.
On a point of ATC interfering at the wrong time, what would you prefer, a couple of questions every few mins, all the questions at once for you to answer when able, or for us to just say we have questions, and wait for you to come back?? Bear in mind, for some pieces of info we need to know immediately, ie FL needed, and diversion adme if its close so they can get all services present. For instances of engine failure, knowing if it was a routine shutdown, or due fire, and if fire still burning etc is needed, and this also prompts which way do you wanna turn (hear that fire determines this now) all the things we need to know to be able to give you the safest a/c free path possible. As has been said so many phone calls take place to organise this our time is crutial too, not forgetting the recall of staff to man a discrete frequency. We may have many bodies around to help, doesn't mean its any easier
