Thomas Marovich died on July 21, 2009 when he fell while performing routine helicopter rappelling proficiency training while assigned to the Backbone fire near Willow Creek, California. On October 2, 2009 the Occupational Safety and Health Administration (OSHA) issued “serious” and “willful” violation notices to the U. S. Forest Service for the incident.
The USFS has just released their Preliminary Aircraft Accident Investigation Report which was completed on October 19, 2009, and a Safety Action Plan dated February 1, 2010. The report is 63 pages long, but I will mention a few of the key points. [UPDATE 9-13-2011; the Lessons Learned Center removed the two reports from their site at the direction of the U. S. Forest Service, who said they were not intended to be released to the public. They replaced the two reports with the National Transportation Safety Board narrative.]
A proficiency rappel is required every 14 days to maintain technical competency. Marovich was in his first season rappelling and was about to make his 11th rappel.
Before the rappelling training, Marovich noticed that the Kong clip on his Tri-link was broken. The Kong Clip is used to center the “J” hook at the forward corner of the Tri-link. It is a nice piece of equipment to have, but is not essential. Kong clips are prone to breaking and are not popular. He sought assistance from a spotter trainee who replaced the Kong clip with an “O” ring, which was an authorized substitution. If I interpreted the report correctly, the “O” ring was installed incorrectly.
Here are some photos from the report showing for illustration purposes examples of a correct and then an incorrect installation of an “O” ring on a Tri-link.
Before the rappelling attempt, four people looked at or inspected Marovich’s rappelling gear: the spotter trainee who installed the “O” ring, Marovich, and in the helicopter a spotter, and another helitack crewperson who did a “buddy check”.
Marovich fell, unarrested, shortly after stepping out onto the helicopter skid. He was pronounced deceased about 30 minutes later.
The Human Factors section of the report, beginning on page 33, is particularly interesting. Written by Jim Saveland and Ivan Pupulidy, it discusses, along with other issues, the concept of not seeing elements in our visual field, or “blindness”.
Below are some quotes from that section:
A misconfigured harness is a very rare event. Wolfe et al. (2005) demonstrated that when a target is rare, participants are surprisingly poor at detecting it. The rarity of the target leads to “disturbingly inaccurate performance.” Rich et al. (2008) explored some of the possible mechanisms for why we miss rare targets, one of them being ending the visual search prematurely. Research in visual attention has also revealed several ways that people don’t see what is in their visual field. This is simply how the human visual system works.
Inattentional blindness is the “looked-but-failed-to-see” effect. It occurs when attention is focused on one aspect of a scene and overlooks an object that is prominent in the visual field and is well above sensory threshold.
Change blindness is a failure to notice that something is different from what it was. Large changes to a visual scene are very likely to go unnoticed if they occur during saccades (eye movements) because visual analysis is suppressed during that time.
Confirmation bias is a tendency to search for or interpret information in a way that confirms our preconceptions/expectations and to ignore, not look for, or undervalue what contradicts our preconceptions. Hollnagel (2004) states that this feature of human thinking (a strong tendency to look for confirming evidence) is an example of the Efficiency-Thoroughness Trade-Off (ETTO) principle. Klayman and Ha (1987) state that some confirmation bias results are due to over-application of a positive test strategy. A repeated review of an established condition (e.g. a correctly configured harness) reinforces the expectation that the system is in that specific configuration. This is an example of reinforcement through experience which leads one to miss potentially critical anomalies.
The existence of inattention and change blindness, as well as the influence of expectations on vision (confirmation bias), helps us make sense of this tragic event.