Wednesday, 14 December 2016
HOW SAFE IS YOUR SAFETY ALTITUDE?
Acknowledgements: GASCO Flight Safety/CFI Adele Stephenson
Unlike in commercial aviation, where such things are generally prepared for the pilot by others, the private pilot needs to spend a considerable amount of effort and thought in order to determine a safety altitude for each flight.
The chances are, if the pilot wants to short-cut the process he or she will nominate a height which is too high (“Oh well, two thousand feet will do!”).
So when the unexpected weather appears ahead, what about that 2000 feet? It gives a good margin above high ground and obstructions, so why not slip below it for a bit to see how far ahead this weather extends?
This is the danger point, since once the decision is taken to descend below your nominated safety altitude there are no further limits; only collision with high ground or obstructions. So once you have descended to your nominated safety altitude that is exactly what it is. Either maintain it, or initiate your Plan B. (Ed. Note: You do have one, right?). Return or divert, without any messing about or “ducking below”!
So, your planned safety altitude has to be:
· realistic, so that it removes all temptation to ignore it
· set below your cruising altitude (this may seem too obvious to mention, but the advice “if you are lost, climb to your safety altitude … “ is known to have been uttered by at least one instructor! But why would you be flying below it in the first place, even in clear conditions?
There are so many things to consider in advance throughout your planned route, both to destination and selected diversion point, including:
· the Law
· low flying restrictions, for noise abatement or any other requirement
· specified minimum altitudes over built-up areas
· clearance above charted obstructions
· high ground
· topological up-draughts & down-draughts, which have adversely affected many a light aircraft
· is your flight routed upwind of or on the lee side of high ground?
· do you need to work to different safety altitudes for different sectors of your flight?
· how far on either side of your planned track do you need your safety altitude to cover in order to account for divergence?
The time spent in pre-flight consideration of the ground conditions over which and close to which you will be flying will be well-spent in the event of need, so please give your safety altitude the respect it deserves, and once off the ground discipline yourself to honour it - it may even save your life!