The County of Orange says that planes will take off to the east, away from Irvine - for noise reasons.
Both the Air Line Pilots Association and the Allied Pilots Association have stated their objections to east takeoffs - for safety reasons. They cite runway slope, mountainous terrain and unfavorable prevailing wind direction factors.
The FAA says "in the interest of safety", pilots can request and receive permission to takeoff in another direction, i.e.. over Irvine. See the FAA manual excerpt below:
The FAA Air Traffic Control, manual (FAA Document No.7110.65) defines the standard tailwind component for aircraft operations as follows (Section 3.5.1):
"except where a runway use program is in effect, use the runway most nearly aligned with the wind when 5 knots or more, or the calm wind runway when less than 5 knots, unless use of another runway:
(a) Will be operationally advantageous orNote-
(b) Is requested by the pilot.
(a) If a pilot prefers to use a runway different from that specified, (s)he is expected to advise air traffic control.
(b) At airports where a runway use program is established, air traffic control will assign runways deemed to have the least noise impact, if in the interest of safety a runway different from that specified is preferred, the pilot is expected to advise air traffic control accordingly. Air traffic control will honor such requests and advise pilots when the requested runway is noise sensitive."
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