Tutorial: Approach Judgment in the Great Basin

Dealing with Runway Slope

Many visiting pilots experience difficulty judging approaches when flying in the Great Basin.  As with so many other difficulties in aviation, the problems are in the basics and stem from the way so many pilots are taught to fly.

A great number of pilots who learned to fly in locations with little or no terrain relief were taught to judge approach slopes by reference to the apparent shape of the runway, that is, by eyeballing the vertical angle between the runway surface and the approach path.  However, the sailplane (or any other heavier-than-air aircraft) “sees” the approach slope as the vertical angle between the horizontal and the approach path.  What’s the difference?  Approaching a flat, level runway, there’s no difference at all.

But “flat” and “level” are two different things, and here in the Great Basin plenty of runways are reasonably flat, but very few are level.  Many of our runways are built on alluvial fans and while they’re often pretty flat, they’re by no means level; they often have appreciable slope.

Flying an approach to a sloping runway, under the assumption that the angle between the approach slope and the runway is the controlling factor, has resulted in numerous accidents and close calls.  It leads to extremely shallow approaches to uphill runways and to excessively steep approaches to downhill runways.  The latter situation is conducive to both overruns and, worse yet, stall/spin accidents.

Flying an approach by reference to the vertical angle between the horizon and the approach slope will always work, regardless of the terrain.  It will work in flat country as well as in the Great Basin.  It’s the safest and most professional way to judge a visual approach, bar none.