any P-3 guys wanna confirm this? i mean, it IS wikipedia and highly doubt improper info to be posted...
"Engine loiter shutdown
On many missions, an engine is shut down (usually engine 1 - the port outer engine) once on station to conserve fuel and extend the time aloft (and range when at low level). On occasion, both outboard engines can be shut down, aircraft weight, weather, and remaining fuel permitting. Long border patrol missions can last over ten hours and may include extra crew. The record for a P-3 is a 21.5 hour flight undertaken by the Royal New Zealand Air Force's No. 5 Squadron in 1972.
Engine 1 is the primary candidate for loiter shutdown because it is the only one without a generator, and is not needed for electrical power. Eliminating the exhaust from engine 1 also improves visibility from the observer stations on the port side of the aircraft."
http://en.wikipedia.org/wiki/P-3_Orion