Your Margin of Safety?

Given a preflight situation, can you concisely define your personal limits?


When was it, to avoid compromising personal limits, you decided not to fly? Sure, serious deteriorating weather conditions are an obvious one. As I write this, severe turbulence SIGMETS from surface to 5000 feet have been issued over northwest Europe, which for me is an obvious “no flight.” But there are some diehards (or dare devils) out there, who are willing to give it a try anyhow. What I am referring to is the whole menu of personal limits. What are they, and how do you deal with them?

The more I thought about my personal limits, the longer the list became. The personal limits of a general aviation pilot with many years of experience, perhaps thousands of hours in the logbook, can’t be compared with a pilot who flies just enough hours a year to stay current. But even then, it is only the next hour of flight that counts.

Personal limits are a crucial part of the decision making process and form the basis for setting the margin of safety during flight. Personal limits should be part of your risk assessment process and it is up to you to take actions to mitigate anticipated risks. My limits fall into the following six categories: flight preparation (weather, airplane and airports), takeoff, en-route, approach and landing and last, but not least, myself. You might order them differently.

I decided to add, on top of the legal requirements, 30 minutes extra fuel reserve. I automated that in my flight planning tool. When doing weight and balance computations I want accuracy in estimating the weight of passengers and baggage. I don’t accept takeoff and landing weights that are even a fraction outside the envelope. I verify that the GPS database, applicable paper airport plates and sectional charts are current. My iPad mini remains the back-up, because this device can quit for a variety of reasons—high temperature during the summer in the South of France has shut it down.


It may be that weather presents the most difficult factor to assess as there as so many aspects to consider. For example, will your flight plan cross an active front—most light aircraft without oxygen and de-icing equipment will probably not handle this in the winter months. Is it a situation where you will say “no problem” or does this give you pause to think about possible avoidance or having a Plan B in case of serious CBs, icing or turbulence issues?

When reading about weather related accidents, how many of those could have been avoided. If serious situations like fronts, squall lines, embedded CB’s, icing, turbulence, low ceilings, fog, and etc. had been classified by the pilots as “I don’t go, unless…” there would be less bent aluminum.

Runway width, length and contamination are on my list. The same is true for airports in mountainous terrain with no STAR and/or SID procedure. Again these limits require a mitigation plan or are a “no flight” item.

Marginal weather can be difficult to assess during the departure for an IFR-flight at a non-towered airport. What about specific published operating limitations of the aircraft like the climb gradient based upon a calculated high density altitude in mountainous terrain? Or just before takeoff, you notice a malfunction of one of the instruments? What about single-pilot or a visual approach in marginal conditions during night IFR? Limited visibility during takeoff and landing? Are you crossing open water for more than the calculated glide range to either shore with a single-engine airplane? With few exceptions these are simply yes or no decisions. It is all in the your hands.

I rarely hear a pilot respond to ATC with “unable … .” There is a tendency to comply with the ATC-authority while at the same time adjusting our personal limits and thereby possibly decreasing the margin of safety.

Examples are ATC-requests for a visual approach in marginal weather conditions or at night; the “feared” threshold- or mid-runway base leg approach at Amsterdam-Schiphol; the LAHSO-procedure, a hold with low fuel status, takeoff and landings with a bit more than acceptable tailwind; and the list goes on.

Personal Considerations

Are you current as a pilot and safe as a person to fly today? It’s not only about the legal requirement here. Do you, given the weather forecast, flight preparation, status of the airplane etc; feel comfortable and competent to make this flight.

The IAMSAFE-check is supposed to be a help to test your ability to fly. Issues like medication, eating, drugs and alcohol should be relatively easy. But what about illness, stress and fatigue? The personal well being of the pilot is one of the most crucial factors for a safe flight. When researching the NTSB-database over the past 24 months, I noticed many flagged medication issues. Not surprisingly, in July the FAA started a campaign to warn pilots about Over-the-Counter medications—based upon a study suggesting that “…these medications played a role in 12 percent of fatal general aviation crashes in the past decade.”

Stress and fatigue are also tricky ones. You can’t “see” them, but they can “bite” you at a critical moment. Being aware of these risks, is the best way of dealing with them. For me this means always a safety pilot during a business trip, regardless of weather or familiarity with the route.

For most of us flying provides enjoyable personal transport or a means for efficient business travel, but it isn’t our profession and it has its risks. As part of the risk assessment, setting (and sticking to) personal limits should add measurably to safety. Some would argue that this is so basic and common sense, so why go through the ritual? I question that attitude as the accident rate doesn’t give me great comfort. I often ask fellow pilots what their personal limits are on a given situation. The response that follows is often long and meandering and not at all to the point—and that is my point.

No Personal Limits?

Consider the 52-year-old private pilot with an instrument rating who, with his wife, decided to go back home after visiting their daughter. However, a fast moving cold front was on its way and penetrating the planned return trip. The pilot called Flight Service to file an IFR flight plan. Although updated weather was offered, the pilot was not interested in the latest seriously deteriorating conditions and gave the impression he already had the information.

That morning a severe weather forecast alert was in force. Significant thunderstorms with hail, wind gusts to 70 knots, extreme turbulence, and cumulonimbus cloud with tops to 50,000 feet were forecasted and a tornado watch was in effect.

Just 29 minutes after take-off the Bonanza hit a line of severe storms and broke up so badly that the parts covered 15 miles. During the investigation it turned out that the pilot had previous encounters with severe weather situations, nearly leading on both instances to in-flight breakup. After the second incident the pilot was required to take special training and a FAA 709 ride, which for two years seemed to be the cure until this last fatal flight.

His wife refused to join him this time and took a commercial flight. She had set a personal limit and more importantly, stuck to it (IFR-Refresher, August 2012).

Klaas Wagenaar has both a rotary and fixed wing PPL with an FAA IFR-rating. He owns a Beechcraft Bonanza F33A, which he uses for business and pleasure across Europe. His writings focus on human factors.

This article originally appeared in the January 2014 issue of IFR Refresher magazine.

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