Christmas tree (aviation)

A "Christmas tree" was a type of alert area constructed by the United States Air Force for the Strategic Air Command (SAC) during the Cold War. Oftentimes, bombers or tanker aircraft were stationed next to a readiness crew building (RCB), also known as "mole hole" facilities. The alert apron, also known as an alert ramp, received the name "Christmas tree", because in planform it resembled a tree of the same name.

Before the development of the Boeing B-52 Stratofortress, aircraft such as the Convair B-36 Peacemaker, Boeing B-50 Superfortress and Boeing B-47 Stratojet were parked on alert aprons at right angles. Due to the size of the aircraft, this created a problem in launching aircraft efficiently in the event of an emergency scramble, requiring a different solution to be devised. To fix this, aircraft were repositioned on specifically designed alert aprons arranged in herringbone configurations, which then allowed the planes to pull out onto the runway as quickly as possible.

This meant that the aircraft would be positioned at 45 degrees in relation to an alert apron center-line leading to a short taxiway and then onto the nearest runway(s). Two aircraft would be positioned on either side of the center-line, typically four deep on either side, with one additional aircraft being positioned directly aligned on the center-line farthest back. The success of this formation also led to the adoption of the setup for the Boeing KC-97 Stratofreighter and KB-50 Superfortress aerial refueling aircraft. As newer bomber and aircraft eventually entered the SAC inventory, the "Christmas tree" aprons would be used by the B-47 Stratojet, B-52 Stratofortress, Convair B-58 Hustler, General DynamicsFB-111, Rockwell B-1 Lancer, Boeing KC-135 Stratotanker and McDonnell Douglas KC-10 Extender aircraft.

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