Tuesday, July 6, 2010
Is Glass Safer?
Making sense of the NTSB glass-cockpit report
Keeping in mind that although incomplete hour estimates were used to come up with the following numbers, they do provide some insight into the safety of glass versus conventional airplanes (also note that the response rate was better for glass users, therefore, in theory, those numbers should be a better reflection of reality than conventional numbers). Between 2006 and 2007, the accident rate (per 100,000 flight hours) in glass was 3.71 and for conventional it was 3.77. So glass airplanes (or at least this group of them) were, overall, safer. However, the fatality rate says something different. Among glass aircraft, the fatality rate was 1.03 (per 100,000 flight hours), but the conventional cohort had a rate of 0.43. Before passing judgment, it’s important to determine if they’re comparing apples to apples.
The many advantages of glass come at a cost other than money: time. Time is required for training in order to develop proficiency.The NTSB identified several attributes concerning the way glass airplanes are flown, and by whom, that differ from round-dial aircraft. One is that glass airplanes are significantly more likely to be flown on an IFR flight plan and thus are logically more likely to encounter instrument meteorological conditions. Another is that glass airplanes are significantly more likely to be conducted on personal or business trips, while conventional tend to fly on a lot more instructional flights than glass types. The highest certificate held in glass is most likely to be a private, while in a conventional aircraft included in the study, there were many more student pilots in the mix. So from the start, you can see that the two groups that were evaluated aren’t at all comparable.
What’s the solution? Compare glass aircraft to other aircraft that are being operated in a similar manner. Looking to the 2009 Nall Report (that looks at the previous year’s stats), data can be extracted to use for a more reasonable assessment. Considering glass aircraft are used more for personal and business trips, it would be wise to compare glass accident rates to other aircraft flown on such trips. The general aviation fatality rate among personal and business flights was 1.89 overall versus that of glass which was 1.65. Not bad. The lethality of glass crashes, the likelihood you’ll die if you crash, was 31.2%. That sounds bad, but we need to put even this in perspective. Considering that glass airplanes are flown in instrument conditions more often, one would expect their lethality to be more similar to aircraft involved in accidents under those conditions than in general. The lethality for IMC accidents in 2008 was 75%. So the 31.2% for glass doesn’t look so appalling when the way the aircraft is normally flown is considered. Also, private pilots are involved in 50% of all accidents of which 52% are fatal. Student pilots, on the other hand, were involved in only 8% of accidents, of which 3% were fatal. Again, when considering most glass are flown by private pilots, one would expect a lethality rate higher than the entire accident population and more similar to that common among the type of pilots flying the aircraft.
What does all of this mean? First, the NTSB provides some great fodder for discussion. They conclude that we need better training for glass. I doubt anyone can disagree with that. But I truly believe that glass, in the hands of a competent, well-trained pilot, has the potential to make flying safer. A moving map with terrain and weather on it certainly can boost situational awareness. The NTSB report also purports that glass is somehow not as safe as similar make and model round-dial aircraft, primarily leaning on the fatality rate to make such a claim. Yet it’s hard to argue with the raw numbers that indicate glass aircraft are, in fact, safer than the average of general aviation and among aircraft flown under similar circumstances.
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