To Err is Human

And also a grim sport many pilots play. Why conservative decisions have their place in the cockpit


For years Ive taught seminars on preventing human error to airline pilots, military pilots, fire fighters, bomb squads, search and rescue teams, smokejumpers and other teams involved in high risk activities.

One of the major portions of this seminar looks at decision-making, including some of the weaknesses and pitfalls of many peopl experience. Although the exact number may vary, depending on which study you quote, pilot decision-making is generally faulted in 85 percent of all aviation accidents.

At scientific conferences, academics and accident investigators hammer on pilots for faulty decision-making that lead to an accident. Ive often sat there quietly squirming because Ive done many of the same acts, just like thousands of other pilots, and have been lucky enough to avoid bending any metal.

Take the Delta Air Lines L-1011 accident in a microburst over Dallas-Fort Worth in 1985, for example. Every pilot flying the line has flown through similar clouds hundreds of times and received just a healthy jolt from the updrafts and downdrafts. On that unfortunate approach, that crew happened to fly into a cloud that within minutes grew from a large cumulus cloud into a thunderstorm.

Unfortunately, in the real world, pilots have to take situations that have uncertain probabilities and make a black or white decision whether to go or not go. How many weather forecasts in the summer contain a chance of afternoon thunderstorms? Its hard to make a black or white decision when flight service says there is a chance of thunderstorms or icing. If you knew for certain that a thunderstorm was a certainty during an upcoming flight, then your decision would be much easier.

One way to try to head off disaster is to subscribe to the philosophy of making the most conservative decision. (In your flying, anyway. Well leave politics out of this discussion.) Simply stated, the most conservative decision is taking that action which avoids the most risk. Much of aviation is about managing risks. The concept of the most conservative decision induces you to take the route of least risk. Its usually a fairly easy mental process and prods you into the safest action.

Wrong Place, Wrong Time
An unfortunate case study where this decision-making technique could have prevented a catastrophe involved friends and acquaintances on an EMS helicopter at a nearby ski resort.

On Jan 11, 1998, a skier was seriously injured in an avalanche. Ski patrollers worked furiously to bring the injured skier downhill to the base of the ski area. The ski patrollers were fighting horrendous winds and oncoming darkness. The incoming weather was predicted to be horrendous, with blizzard-like conditions.

The EMS helicopter was dispatched to the ski resort, which is located about eight miles up a deep narrow canyon from Salt Lake City. Snow was not falling when the helicopter departed the hospital, but there were gusty winds and light to moderate snow during its arrival at the landing zone at the base of the ski resort.

Due to the poor conditions on the mountain, it took ski patrollers a long time to bring the injured skier down the mountain. The dispatcher telephoned the pilot using a cellular phone to advise him that hospital weather conditions had deteriorated due to the fast-moving front. She said it was snowing really hard, with the winds gusting to 37 knots and the visibility had dropped to less than 300 feet.

She could not see a wing of the hospital on the closed circuit television monitor and could barely distinguish the helipad. The 10 p.m. evening news report from the base of the ski resort showed the weather was quickly deteriorating. The local weatherman showed the radar report and the sharp-edged weather that was due to hit the valley in minutes.

It was unknown when the ski patrollers would arrive at the base of the mountain. At the end of the evening news, the reporters said that the injured skier was due to arrive at any time, though in the background you could see the swirling snow as the weather front had clearly moved over the ski resort. Shortly thereafter, the ski patrol arrived with the injured skier and loaded the injured skier onto the helicopter.

A sheriffs deputy said the helicopter took off from the landing zone in blizzard conditions and circled the landing zone, then turned north and disappeared from view. Seconds later, a deputy heard a slight muffled boom. Later, in daylight and better weather conditions, the helicopter was found where it had struck the mountains. The four occupants were killed in the crash.

Many of the ski patrollers were friends, so I awoke early and turned on the morning news to see if there were any updates on the rescue of the skier. It was a sad morning when I saw the grim faces of the TV reporters who carried the story of the late evening crash of the helicopter. Ironically, I had just spent several afternoons discussing and sharing safety information with that pilot a few weeks earlier.

The pilot probably took note of the hostile terrain, failing light and worsening weather. Somewhere in his brain he probably recognized that it would be less risky to get out of the canyon before the weather moved in and have the injured skier transported by ground. It would have taken at least a half-hour longer to get the skier to the hospital, though in this case the helicopter never made it.

Its easy to be a Monday morning quarterback in analyzing anyones decision, but this is one clear case where a more conservative decision would have paid off.

There are many situations where the most conservative decision would apply easily. One of the first that comes to mind is fuel, because it is usually resolved in an easy manner.

Fuel gauges are inherently unreliable in light aircraft, so often pilots are left wondering how much fuel is left in the tanks. Its best to always leave the departure airport with a known quantity of fuel, whether thats through the use of a calibrated dipstick or ascertaining the tanks are full. Its also prudent to never plan a flight based on the manufacturers advertised cruise speed and fuel consumption. Always add a safety factor into those numbers.

Depending on the airplane and the flight involved, you may also want to consider planning to land for fuel when youre down to a third of your capacity, particularly when flying IFR or cross country.

If you are flying en route and are getting concerned about the quantity of fuel in the tanks, dont hesitate to ask yourself what the most conservative course of action would be. If there is any doubt, divert to an airport where you can refuel. It might add 30 minutes to your travel time, but thats a far better alternative than having the engine sputtering while youre in the traffic pattern.

Unfortunately pilots often frame their questions so that it points toward another course of action. You think about the appointment waiting at your destination or the weather youre trying to beat. You may bump up the power setting a bit and actually worsen your fuel situation. Remember that Murphys Laws are lurking out there. As soon as you start shaving your safety factors, Murphy will definitely spring his traps.

Increased headwinds, air traffic control delays, closed runways, worsening weather – all of these can quickly change your fuel situation from having an adequate supply to an impending fuel emergency.

Get-home-itis has been in the aviation training material almost as long as airplanes have been in the air. Its frustrating to sit on the ground when you have an appointment out of town, or after being on the road and you just want to get home.

During a recent study of EMS helicopter safety, I found that the vast majority of fatal accidents occurred in marginal weather with low visibility – a disturbing trend that hasnt changed much since EMS helicopters became popular in the 1980s. The most common fatal accident was a night mission over rugged terrain without the ability to go IFR. The helicopter ended up flying close to the ground in marginal weather with no weather reporting stations along the route.

The risks are pronounced during such an operation. If an engine fails, the pilot is forced to make an emergency landing in mountainous terrain at night. It is far too easy to inadvertently enter IMC at night and become spatially disoriented. When the weather is marginal, around three miles of visibility, its easy to suddenly realize youve entered IMC. Many of the EMS accidents at night have hit wires, which tells you how low they were cruising in order to avoid the weather.

Since the IFR enroute structure isnt designed for point-to-point helicopter flying – and given some of the other limitations of helicopters in IMC – the most conservative decision during marginal weather is to stay on the ground. While that runs counter to the emergency medical services mission, its better for flight safety. In operations with fixed wing aircraft, flying IFR with equipment that is capable of handling the weather is more practical, depending on how close the airport is to the hospital. Given the number of IMC-related accidents in EMS flying, particularly at night, the industry really needs to re-assess the risks of these decisions and make some changes.

The same logic applies to recreational flying. If incoming weather is beyond the capabilities of yourself or the aircraft, it is far safer to stay on the ground and wait for the weather to improve. Even experienced IFR pilots making business flights need to take a hard-nosed look at themselves and their equipment.

Inoperative Equipment
There are a lot of airplanes flying that do not have every single component in perfect working condition. The digital timer may be missing a segment or the DME might not capture a certain frequency range. How about excessive precession in the heading indicator? In Part 91 flying, you are allowed to fly with inoperative components on the aircraft provided the device isnt required for the flight. For example, if you are flying at night, position lights are required, but they arent for day flying. There is a lot of leeway for judgment in Part 91 operations.

If the weather is severe clear and youre out in the middle of farm country, you can get away with surprisingly few instruments. As a glider flight instructor, I often covered up most of the instruments so the soaring student would learn to use his senses for flying the aircraft. The loss of an airspeed indicator really shouldnt be that much of a problem if you are familiar with the aircraft.

But lets say flight service forecasts the possibility of some marginal VFR weather and you dont have a high level of confidence in the operability of your turn coordinator or nav receiver? Perhaps the radios are weak or the anti-icing boots dont work very well. Why take the risk? The most conservative decision is to wait until the weather clears enough to make the flight.

Structural Integrity
You may not think youd ever consider flying an aircraft with suspect structural integrity, but some pilots have knowingly been pressured into it. The pilot of one Pitts S1S had voiced concern about the airplanes wing because of flutter he had experienced during recent flights, but he flew an airshow anyway.

The pilot initiated his first maneuver, a double snap roll. A videotape of the maneuver showed a deformation of the lower left wing within seconds. This was followed by a failure of the left outboard portion of the upper wing, which displaced against the empennage.

The audience watched in horror as the aircraft fell to the ground. If you have any doubt at all about the structural integrity of an aircraft, keep it on the ground.

Soft Fields
Several years ago, I landed on a friends Montana ranch after looking for some lost cattle. I chose to land in his hay field adjacent to where he was cutting hay. I had walked that field earlier in the morning admiring the condition of the grass and chasing some bulls.

The field was well irrigated that summer because of an abundance of winter snow, so the grass was slightly long and the ground was slightly wet. When I landed, I touched down softly and tried to get a feel for the ground before retarding the power fully.

The drag of the grass was fairly pronounced, so I decided to go land on a field that was on a slanted hillside. It received no irrigation so I assumed it would be drier ground. Additionally, his cattle had grazed the hillside so the grass was shorter.

Even so, the underlying soil was much softer than I had realized. I managed to taxi the aircraft over to some drier, harder ground using more power than normal while antelope sprinted around the aircraft.

When I look back at this decision, I was lucky that the ground wasnt softer. Ive written about the hazards of landing on unimproved strips and many of those lessons were learned from experience. Its very important to inspect the condition of a soft field before you land. Many back-country pilots will inspect the strip by doing a high recon of the strip first, and then doing a low recon. In the back country, that may be the best you can do.

However, under most normal general aviation operations, you should inspect the field first by physically walking around on the airstrip before operating on the strip.

The hazards are frequently very difficult to distinguish from the air. It may be tempting to land on that airstrip that looks like something Tiger Woods may use for putting practice without checking it out first. In your last 99 soft field landings you may have encountered no unseen or unanticipated problems, but Murphys Law is hiding in that tall grass. It may contain tall wet grass, hidden soft spots in the ground or hidden rocks.

In this situation, frame your decision-making this way. The most conservative action is to land on a nearby paved airstrip, grab the courtesy car and check out this airstrip.

One of the methods that sailplanes use to remain airborne is to circle in rising currents of hot air, or what sailplane pilots call thermalling. Soaring is very challenging, and often sailplane pilots find themselves getting close to the ground when trying to find another thermal.

Its tempting to try circling in a possible thermal to try to climb out. Unfortunately, soaring has a very high rate of stall/spin accidents, and low altitude thermalling is a prime environment for this to happen due to several factors.

Ive heard some pilots talk about thermalling at 100 feet. Imagine making 45-degree banked turns just 100 feet above the ground in a gusty thermal. No thank you.

A general guideline in soaring that applies equally well to a simulated emergency landing in a powered aircraft is to have three possible landing fields in your mind when you are above 3,000 feet agl. As you descend, narrow that to two fields. Once you pass through 1,000 feet AGL, you are committed to landing on your prime choice. There have been enough accidents where the pilot changed his mind at the last minute and was too close to the ground, causing the aircraft to stall/spin.

Making steep turns close to the ground is definitely not safe, whether thermalling in a sailplane or flying a pattern. For a sailplane, the safest course of action will normally be to execute a landing in the field, take off the wings, put the sailplane into a trailer and haul it back to the airport for another flight.

Part 91 flying should be fun and useful, but it shouldnt give you ulcers. If you arent certain you can safely accomplish the flight operation, then take the most conservative action. If youve been given tight vectors behind a 757 or heavy airliner, take the most conservative action and back off. If youve received a forecast of marginal weather that you or your aircraft cant handle, take the most conservative action and wait for better weather.

If an inoperative aircraft component is needed for the safety of a particular flight, get it fixed. If the runway is icy, choose a runway with less ice. If the crosswind is more than you are comfortable with, go land on a runway where the crosswind is less.

Remember there is a lot of truth to the statement that you would rather be on the ground wishing you were flying than in the air wishing you were on the ground.

-Pat Veillette

Pat Veillette is an aviation safety researcher who flies Part 121 cargo jets in his spare time.


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