Effective Area Calculations.

DOE-STD-3014-96

APPENDIX B

B.4

The effective area represents the ground surface area surrounding a facility such that if an

unobstructed aircraft were to crash within the area, it would impact the facility, either by direct

fly-in or skid into the facility. The effective area depends on the length, width, and height of

the facility, as well as on the aircraft's wingspan, flight path angle, heading angle relative to

the heading of the facility, and the length of its skid. The effective area consists of two parts,

the fly-in area and the skid area. The former represents the area corresponding to a direct

fly-in impact and consists of two parts, the footprint area and the shadow area. The footprint

is the facility area that an aircraft would hit on its descent even if the facility height were zero.

The shadow area is the facility area that an aircraft hits on its descent, but which it would

have missed if the facility height were zero.

For this standard, the facility is represented by a bounding rectangle, and the heading of the

crashing aircraft with respect to the facility is assumed to be perpendicular to the diagonal of

the bounding rectangle, as shown in Figure B-3. These assumptions provide a conservative

approximation to the true effective area.

The formula for calculating the skid and fly-in areas for an aircraft crashing into a rectangular

building is given in Equations B-3 to B-5. Details are provided in Reference 1. Table B-16

provides typical wingspans for commercial, general aviation, and military aircraft. Table B-17

provides values for the mean of the cotangent of the impact angle. Table B-18 provides

mean skid distances for each aircraft category. Values of wingspans for selected aircraft,

values of marginal cumulative distribution functions for the impact angle, and aircraft

subcategory skid distances are provided in Reference 2.

B-26