Safety Check | Jan 01, 2018
Observer/Expectation Bias

Jim Crouch

A jumper puts on his rig, boards an airplane and exits the plane at 10,000 feet for a formation skydive with three other jumpers. Soon after the exit, one of his teammates points out that his chest strap is flapping in the wind. It is unthreaded and trailing uselessly behind his back. At deployment time, he manages to hold the two main lift webs together with his left hand and deploy with his right. He lands otherwise uneventfully. The jumper was sure that he checked his chest strap when he went through his multiple gear checks. So if he really checked his gear, what happened?

The likely explanation is observer/expectation bias. This jumper had put on his gear hundreds of times and checked his chest strap, leg straps and handles hundreds of times. His gear check became a thoughtless process, and his brain expected everything to be just as it had been for all those other gear checks. He was looking, but he did not really see. 

This type of error has led to all sorts of incidents in skydiving, as well as in aviation in general. In almost every case, the incident involved someone with a great deal of experience. Observer/expectation bias explains how two highly experienced pilots could land an airliner on the wrong runway or even at the wrong airport. Or how a very experienced rigger could make a fatal packing error to the reserve parachute system, even though the error is obvious in a simple gear check. Most of the time, the enemy is simple complacency and allowing our eyes to see what we think we should be seeing. However, we should always expect the unexpected and look carefully at our surroundings.

In dozens of instances, highly experienced jumpers missed seemingly obvious problems. The tandem skydiving industry has seen its share of accidents when experienced instructors missed an obvious problem such as a riser flip-through (a common problem with tandem main-canopy risers), a misrouted drogue release system or another glaring gear error. Even highly experienced tandem instructors have missed these problems during the gear check, walk to the airplane and climb to altitude, even when surrounded by other highly experienced instructors who could have caught the problem. In many cases, those who review the video after the fact and know what to look for find that the problem is in plain sight and obvious. 

A misrouted chest strap is probably the most common example of an error caused by jumpers who fall into the trap of observer/expectation bias. It does not take much for a jumper to fail to thread the chest strap through the friction adapter, and to the casual observer who is not really paying attention, the chest strap may still look like it is routed correctly. Each jumper expects that he has put his gear on correctly. 

Although it is a constant battle, skydivers must work toward eliminating errors caused by observer/expectation bias. If you are just going through the motions with your gear checks, get back to really paying attention! Take a few seconds to check your gear without any interruptions or distractions, to help you stay focused. Whether it is gear checks or any other part of skydiving, learn to look carefully so you can see what your eyes are really observing. 


Jim Crouch | D-16979

USPA Director of Safety & Training  

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