Let's make a few assumtions here;
1. The aircraft is cruising West to East and is therefore likely to be at 37000' (B747).
2. The aircraft is directly above your head when you first spot it.
3. A B747 typically cruises at 8nm per minute.
4. We shall assume 'still air'.
5. We shall ignore the curvature of the Earth.
Therefore;
When you first spot the aircraft it is 37000' away from you.
After 10 minutes the Aircraft is 487805'(or 92.3 statute miles)away from you by line of sight.
[Use of Pythagorus' Theorm where -
1 Statute mile = 1nm x 38/33
1 Statute mile = 5280 feet.]
[This message has been edited by Icarus (edited 17 March 2001).]