A few weeks ago, Flight School Business reported an oddity that popped out of an analysis of accidents in late-model examples of several current primary trainers: Cessna 172s suffered more landing accidents than single-engine Diamonds or fixed-gear Cherokees, thanks almost entirely to a much higher number of arrival stalls and other hard landings. The pattern was consistent enough to be credible despite relatively small numbers of accidents in the two low-wing models.
The data behind that finding was limited to airplanes manufactured during the past 10 years, but included all levels of pilot certification and all types of flights. Since then, the Air Safety Institute has gone at this from another angle. An ongoing analysis of instructional accidents treats primary training separately from advanced instruction and distinguishes between dual lessons and solos. Accidents on solo flights by pilots working toward advanced certificates are hard to identify, but the record of primary instruction is fairly complete.
To no one’s great surprise, the airplanes that show up most often in primary instruction’s accident record are the ones most widely used: the 172, with a total of 518 accidents between 2002 and 2011; the two-seat Cessna 150 and 152, which saw a combined 252 accidents over the same 10-year period; and (again) the fixed-gear PA-28 series, with 144 accidents during that time. (Only 24 instructional accidents occurred in the two single-engine Diamond models, but the total number of DA20s and DA40s registered in the United States is barely 5 percent of the number of either Skyhawks or Cherokees.)
None of this tells us much about the actual risk of training in these airplanes. Figures on the numbers actively flown are sparse, and there’s no reliable data on how many are used for transportation versus teaching or how many hours they’re flown. The 172 is the only one still being built in quantity; production of the 152 ended in 1985, and the General Aviation Manufacturers Association reported that Skyhawk deliveries in 2012 alone (140) outnumbered total Cherokee production over the past five years combined (124). However, comparing the number of accidents on student solos to the number during dual instruction could provide a useful benchmark. The assumption here is that a competent CFI ought to be able to fly any of these with equivalent margins of safety. If you also assume that it’s equally easy for the instructor to take control of each, and that there are no consistent differences in the kinds of students who train in them or the locations or environments in which they’re flown, then you can think of the number of accidents during dual lessons as representing the irreducible minimum risk. Comparing that to the number on student solos may say something about how forgiving—or challenging—different models are for inexperienced pilots.
The results are a bit surprising. The 144 accidents in PA-28s during primary training included 54 during dual flights and 90 on student solos, a ratio of 1.67 solo accidents per dual. Grouping the 150 and 152 together, there were 83 accidents in dual instruction and 169 on solo flights for a ratio of 2.04. And the 525 accidents in 172s break down as 125 during dual and 393 on student solos, a ratio of 3.14. So students soloing the most popular high-wing four-seater of 150 to 180 horsepower had almost double the excess risk of students flying the most popular low-wing four-seater of 140 to 180 horsepower.
As we’ve seen before, the most common type of instructional accident—and far and away the most common on student solos—is the bad landing. Landing smacks accounted for 41 percent of the Cherokee accidents, exactly half of all training accidents in 150s and 152s, and 60 percent of those in Skyhawks. Moreover, the solo-to-dual ratio is 3.5 in PA-28s, 6.1 in 172s, and a whopping 8.7 in the two-seat Cessnas. Skyhawks also saw 4.4 takeoff accidents on student solos for every one during dual; the ratio was only 1.6 for their smaller cousins and just 0.6 in Cherokees.
So far we’ve treated the Cessna 150s and 152s as equivalent, but that’s not quite true, either. It turns out that the number of landing accidents on dual flights was almost equal—six in 150s, seven in 152s—but the number during solos was not. Eighty-five of 113 solo landing accidents occurred in 152s, meaning that the solo-to-dual ratio jumped from 4.7 in the older model to 12.1 in the “improved” version. Reducing flap travel from 40 to 30 degrees did achieve its goal of reducing susceptibility to accidents during go-arounds—eight of 12 in 150s were on student solos compared to just two of four in 152s—but apparently also made the airplane significantly harder to land.
Of course, these are all tricycle-gear models. Since they’re widely seen as harder to land, relatively few students learn to fly in taildraggers these days. But does the extra finesse required translate into more training accidents? Stay tuned!