As the old saying goes, “What goes up, must come down” and in aviation, the coming down part is statistically the most hazardous. From the very start of our training, pilots are taught to know where we are in relation to the terrain around us at all times.
We all love the views out of the window on a beautiful clear day, but how do we know where the terrain is on a nasty cloud-covered windy night?
Through layers of safety systems developed over the years of aviation, we are now better equipped than ever to reduce the risk of controlled flight into terrain — CFIT. From accurate charts to GPS-based terrain avoidance systems, flying on a commercial airliner has never been safer.
How low can you go?
The key element to avoiding inadvertent contact with the ground is knowing where you are at all times. As pilots, not only do we have to be aware of what’s around us in two dimensions, we also have to be conscious of what’s around us in the third dimension — above and below us.
Flying along on a lovely clear day, it’s possible to see the ground below us and it’s easy to identify hills and mountains. However, history has shown that even on days like this, CFIT accidents do still occur. As a result, no matter the weather conditions, we must always be aware of the height of the terrain around us.
However, just knowing the height of the closest mountain won’t necessarily keep us safe. Many of the largest hills are home to radio masts and other telecoms structures which can be hundreds of feet high. As a result, we need to take these obstacles into consideration as well.
In addition to this, like with all things aviation, we also apply a safety margin. Adding all these together, we come up with a minimum safety altitude (MSA) — the lowest altitude which we can fly that we know will keep us clear of the terrain.
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