PILOT DECISION MAKINGLindell Wilson, WVFC CFI LindellWilson@PilotNow.com
Decision Making – Why do Airplanes crash?
Numerous studies have concluded that 70 to 80 percent of aviation accidents are due to human error (pilot error). However, human error is complex and accidents usually cannot be attributed to a single cause. Several studies suggest that aviation accidents are the result of numerous causes, but only the last few unsafe pilot actions trigger an accident.
The “Swiss Cheese” model of human factors developed by James Reason suggests four cascading levels contributing to human failure.1. Unsafe Acts
2. Preconditions for Unsafe Acts
3. Unsafe Supervision
4. Organizational Influences
Reason’s first level is Unsafe Acts of operators (pilots) which is the focus of most accident investigations. An example of Unsafe Acts might be a VFR only pilot entering instrument meteorological conditions.
The second level is Preconditions for Unsafe Acts. One example might be a mentally fatigued pilot who has Get-Home-Itis, becomes fixated on a problem, and/or loses situational awareness.
The third level is Unsafe Supervision. One example might be an inexperienced flight crew that is sent by company dispatch on a flight at night in bad weather.
The fourth level is Organizational Influences. One example might be a flight school that has insufficient or poorly designed pilot/aircraft checkout procedures which might allow unqualified/inexperienced pilots to fly.
Now, let’s look at a real life accident and try to determine where the Reason’s four levels might have played a role. See the notes (1, 2, 3, 4) corresponding to Reason’s four levels.
A family of four begins a flight from Indiana in a Cessna 182A to attend a weekend wedding in Michigan. The pilot was concerned about overall weight, so he carefully calculated the weight and balance, then added just enough fuel (1)and (2) to make the round-trip with 45 minutes reserve. The flight was planned VFR, so the pilot believed he would be well within the regulations and his personal minimums. The pilot had recently installed new fuel gages (2) during an avionics upgrade.
On the return leg, the weather in Michigan was excellent VFR but there were some cloud layers in Indiana. About halfway back to Indiana at 8500 feet, the pilot noticed a cloud layer ahead and decides on a slow descent to 6500 feet to fly below the layer. He wife comments that she is concerned about the “new” fuel gages as they show very little fuel remaining and there is still 40 minutes before arriving at our home airport. The pilot starts to become concerned whether he has enough fuel. Was there a fuel leak? Are the fuel caps on tight? The pilot notices some engine roughness which adds to his concern about possible fuel starvation.
The pilot then noticed a small grass strip below and decides to make a precautionary landing to check out the fuel and rough engine issues. The first approach was high and fast (1) and (2), so the pilot begins a go-around. On downwind the engine stops, the stall horn sounds, left wing drops suddenly, pilot recovers wings level, then lands 45 degrees to the runway. Unfortunately, the left wing touches first and in a nose low attitude causing the nose gear to shear off, the prop to dig into the ground, and the plane flips over on its back (1). Fortunately, the family of four survived with only slight injuries. The FAA, after exhausting other possibilities, concluded that carburetor icing was the problem, not fuel exhaustion. The pilot had not considered that pulling back on the throttle during the descent had contributed to carburetor ice formation.
Ops... Are there any levels (3) and (4)? Possibly, the pilot’s aircraft checkout, emergency procedures, and currency training?
Swiss Cheese - Dr. James Reason (1990), Scott Shappell and Douglas Wiegmann developed the Human Factors Analysis and Classification System (HFACS)