The Human Factor: Assessing Total Risk

The combined effect of small risk factors can add up to disaster.

Human Factor Total Risk

Human Factor Total Risk

Many of the aviation accidents I have written about fall into the “What were they thinking?” category. This would include a noninstrument-rated pilot who takes off into weather that is so bad even the birds are walking; the pilot who continues into ominous weather; and the pilot who tries to take off on a short, high-elevation runway in an airplane loaded far beyond its allowable maximum gross weight. Although there may have been a number of factors that contributed to the accident, there was ultimately one major instigating failure in judgment that would have ordained an adverse outcome even without the other factors.

On the other hand, in many cases there is no "smoking gun," the one significant factor that made an accident inevitable. Often experts are unsure what caused a crash, and even the pilot, if he survived, may have no idea what caused the accident or, if it was pilot error, what led him to make the fatal mistake that led to the crash. In the May issue of Flying ("No Greater Burden"), I wrote about how Russ Jeter landed his amphibious floatplane gear-down on a lake, leading to the death of his young son. Jeter, a very careful and professional pilot, was totally mystified as to why he had neglected to do the final GUMP check that he always does to ensure that the gear is up or down as appropriate. It was only after a specialist in human factors gave him a stress test that he realized he had not been sleeping well after the death of his mother and had felt unusually drowsy that morning. That one subtle factor that he was not consciously aware of, combined with a relaxed flight and the distraction of his son asking him questions as he descended to land on the lake, was enough to cause a momentary loss of focus that allowed him to land gear-down.

The crash of a Cessna P210N on takeoff from Burley, Idaho, in August 2011 provides a classic example of how several little factors can add up to a fatal accident:

1. The private pilot had 480 hours total time and 160 hours in the Cessna P210. There is no information in the NTSB report about how long he had been a pilot or his recent experience, but generally the 500-hour mark can be a risky point in a pilot's flying career, when he may begin to get complacent. This can be especially risky in a sophisticated, high-performance airplane like a Cessna P210.

2. The pilot had stopped at a nearby airport to fill the main and auxiliary tanks with less expensive gas. He stated to his sister that this would allow him to make it home to Southern California with only one gas stop, in Provo, Utah.

3. With the pilot, his wife, two children and approximately 100 pounds of luggage on board, the airplane was estimated to be very close to the maximum allowed takeoff weight.

4. The weather was clear, but the temperature at the airport, which is at an elevation of 4,154 feet, was 91 degrees Fahrenheit (33 degrees Celsius), resulting in a density altitude of over 7,000 feet.

5. The winds at the time of the crash were about 6 knots out of the northeast.

6. On his only previous visit to the Burley Municipal Airport during the winter, the pilot had departed to the southwest on Runway 20 and had initiated a left turn as soon as he was airborne, possibly to give his family a better view of other family members waving goodbye from the ground. Even though the winds were out of the northeast and Cessna performance charts showed that the airplane would barely reach 50 feet by the end of the runway, the pilot again departed from Runway 20, lifting off about 3,000 feet down the 4,092-foot runway, and initiated a left turn after retracting the landing gear. The airplane immediately began to sink toward the ground, crashing into a road and railroad tracks. Everybody on board was killed in the crash, and the airplane was almost completely consumed in the ensuing fire.

When it comes to assessing risk, the combined total risk is often much greater than the individual risk factors might suggest. Basically, one plus one plus one equals about 10 on a risk-analysis scale. In this case, even though the pilot was technically legal and within limits on all risk factors, the combined total effect of those individual risk factors put that pilot in a very tenuous situation on takeoff. Any unanticipated factor, like less than book performance from the engine or an increasing tailwind with altitude, could spell disaster.

Somehow, as this pilot accumulated a moderate amount of experience in his very sophisticated airplane, he lost that aggressive skepticism that is always asking “What could kill us today?” The obvious answer on that takeoff was the density altitude. It is very possible that this was his first takeoff at a high elevation on a hot day. His previous takeoff on a cold winter day had been no problem, and he apparently did not anticipate the risks involved and how differently his airplane would fly in the summer versus the winter, especially with a light tailwind.

If the pilot had accumulated more flight time, he might have scared himself enough times to recover that sense of professional caution that is critical to aviation safety. Ironically, if he had had less experience, he might have still had that caution that leads new pilots to double- and triple-check everything and to take the most conservative response in all situations. Besides the pilot’s experience level, there were five factors that contributed to this accident:

• Full Fuel Tanks — Instead of focusing on saving money by filling up with less expensive gas, the pilot could have instead planned to depart with only partial fuel and made two fuel stops on the way home.

• Baggage — The pilot could have shipped some of the family's luggage home, further reducing the airplane's takeoff weight by up to 100 pounds.

• High-Density Altitude — The pilot could have planned to depart early in the morning, when the temperatures were cooler, rather than at 2:30 p.m., when the temperatures were hottest. The temperatures in Burley are often 30 degrees cooler in the early morning hours, so an early morning departure would have resulted in significantly enhanced performance.

• Tailwind — We don't know why the pilot chose to depart with a 6-knot tailwind. He could have been focused on turning left adjacent to the ramp area again, so his family could see other family members on the ground, or perhaps he was just trying to save a couple of minutes by departing in the direction of his next destination. Maybe because the wind was so light, he figured it wouldn't make any difference.

• Rapid Turn After Takeoff — The most important objectives on any takeoff are maintaining control of the airplane, maintaining the appropriate climb airspeed, and gaining altitude. Any unnecessary maneuvering reduces climb performance and increases risk, especially after taking off at a high-density altitude. It appears this pilot was experiencing macho and invulnerable attitudes, showing off while disregarding the risks involved.

Toward the end of my corporate Preventing Human Error seminar, I say that every time a person or a team experiences any sort of a significant problem, after they determine how they are going to handle the problem they should go back and add up all the other problems and risk factors they have experienced to see if they are sliding into what I call an untenable situation. If this pilot had changed any one of these five factors, he would have probably avoided the accident. Taking the conservative approach and adjusting all five factors would have provided a significant margin of safety for the pilot and his family.

Throughout the process of planning and conducting a flight, there will invariably be risk factors to assess, often associated with problems and issues that need to be handled. In addition to assessing each individual risk factor, it is crucial to assess the total combined risk involved throughout this process to ensure that the combination of several small risk factors does not tip you over the edge into an untenable situation.

We welcome your comments on flyingmag.com. In order to maintain a respectful environment, we ask that all comments be on-topic, respectful and spam-free. All comments made here are public and may be republished by Flying.