A little web research revealed that it is a military flight rule.
From: Wikipedia, Modern United States Navy carrier air operations
http://en.wikipedia.org/wiki/Modern_Uni ... 2FapproachPenetration/approach
In order to maintain proper separation of aircraft, parameters must be precisely flown. Aircraft descend at 250 knots and 4,000 feet per minute until 5,000 is reached,
at which point the descent is shallowed to 2,000 feet per minute. Aircraft transition to a landing configuration (wheels/flaps down) at 10-nmi from the ship.