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HMA TO HA FORMULA
21.06.2006
Submission:
The following explanation of the hma-ha relationship was devised by Red Callaway for his PANS-OPS Workshops. The geometry: is as follows: "x" is the range of the missed approach obstacle with height hma; "xz" is the range of the ground intercept of the missed approach surface; "ha" is the equivalent approach obstacle.
hma*cot Z = ha*cot VPA + ha*cot Z + (xz - x)
hma*cot Z = ha*(cot VPA + cot Z) + (xz - x)
ha*(cot VPA + Cot Z) = hma*cot Z - (xz - x)
ha = {hma*cot Z - (xz - x)}/(cot VPA + Cot Z)
or
ha = (hma*cot Z - xz + x)/ (cot VPA + Cot Z)
Given x and xz measured positive before and negative after threshold.
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