Tuesday, July 6, 2010
Is Glass Safer?
Making sense of the NTSB glass-cockpit report
It’s important to look at how the study was conducted to confirm the soundness of the methodology used. We’ve all heard compelling results of studies or polls that later turn out to be proven wrong or erroneous. This often is caused by researchers using poor technique when inquiring into the subject at hand, or worse, making claims that go beyond what can logically be construed from collected data. Furthermore, if a study is comparing apples to oranges, it’s invalid.
A recent NTSB study concluded that glass-cockpit aircraft were no safer than conventional instrument aircraft. Their recommendation for training on specific equipment is necessary to realize the safety potential of glass cockpits.
Furthermore, the NTSB made no effort to ensure the compatibility of accident circumstances. Simply, they compared apples to oranges. Glass airplanes are generally flown farther than conventional aircraft, deal with different weather conditions, are typically flown by a different pilot cohort, and tend to be used less for instructional flights than round-dial types. Is it fair to compare fatality rates of aircraft flown in IMC versus those flown in VMC, then say, “Aha! Those airplanes that are flown in IMC are more dangerous”? Of course not. Numerous previous studies have shown that flying in IMC is inherently more deadly than in VMC.
The NTSB study looked at 2,848 conventional and 5,516 glass aircraft that were built from 2002 to 2006. There was a wide range of aircraft included in the study, but the big names were Cessna, Cirrus, Diamond and Piper. Then the accident rates of these aircraft from 2002 to 2008 were analyzed. A total of 141 accidents occurred in conventional aircraft and 125 in glass. So which is safer? On the surface, the conclusion is obvious—glass: There were 125 accidents among 5,516 glass airplanes versus 141 accidents among 2,848 conventional aircraft. Unfortunately, it’s not fair simply to just count accidents nor is it fair to calculate an accident-per-airframe ratio. Why? Because if 5,000 of those glass airplanes were sitting in the hangar the whole time, we might change our opinion on their safety. So, accident rates per 100,000 hours are calculated to level the playing field.
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