IFR Fix: The 'flexible safety buffer'

August 22, 2014

A new terminal area forecast has just come out. So far, everything looks good for your hour-long flight planned for the smooth air of tomorrow morning.

A lot could change between now and then, but the developing scenario looks perfect for a getting-back-into-instrument-flying type mission. Destination conditions for your arrival are forecast "04004KT P6SM BKN020" (in plain language,"wind 040 degrees at 4 knots, visibility 6-plus miles, clouds broken at 2,000.")

The light winds forecasted are a plus, because a forecast of "0000" winds would imply a higher possibility of ground fog. But especially encouraging was the six miles visibility; that provides margin above the minimum three miles visibility allowing the flight plan to be filed without an alternate airport designated.

For a pilot who is "legal" but rusty, the dividing line between having to file an alternate or not offers a workable "personal minimum" for a single-pilot IFR go/no-go decision. Consider that if flight conditions were to turn out exactly as forecast, an hour’s cruise above or within broken clouds with bases at 2,000 feet agl, followed by an IFR letdown into clear air below would provide a thoroughly satisfactory IFR experience, without overtaxing your current proficiency and confidence level. 

So here’s a query about situational awareness: At what phase of the instrument approach would you expect the breakout into clear air to occur? Probably it would happen inbound after a procedure turn, or just outside the final approach fix, depending on the approach's type and "architecture."

Uh-oh, an amended TAF has been issued—and it busts your personal minimums. 

That’s not necessarily a deal-breaker. If another instrument-rated pilot can accompany you, would the forecast 1,500-foot ceiling seem acceptable?

How about a 1,000-foot ceiling?

If you find yourself vacillating, consider overhauling your personal minimums so they trigger a certain decision for that contingency, just as a forecast of terminal conditions below "2,000 and 3" mandates filing an alternate.

When it comes to establishing personal minimums, you need a working definition of the term. Don’t confuse setting "minimums" with defining a set of conditions that could take you too close to the limits of safety.

In his August letter to pilots, "Got Weather?," FAA Administrator Michael Huerta urged pilots to write down their personal minimums, noting, "This is your personal, flexible safety buffer based on your skills, training, currency and proficiency. It will help you plan and complete a flight."

Dan Namowitz

Dan Namowitz | Aviation Writer

Dan Namowitz is an aviation writer and flight instructor. He has been a pilot since 1985 and an instructor since 1990.