Trainers Compared

Diamond Katana and Cessna 172 lead the way in training pilots safely


How about a tip of the hat for the long-suffering flight instructor, a hardworking professional who gets neither the respect nor the pay he deserves. And considering the risks involved in teaching a ham-fisted neophyte to fly, we wonder how it is that many survive for long.

Is that a credit to raw skill or the clever design of the average primary trainer? A little of both, we suppose, but from time to time, were asked to rate training aircraft solely on safety records, good or bad.

In a joint research project with our sister publication, The Aviation Consumer, we launched an effort to assess the safety of different models of airplanes. In our first – and we hope not last – analysis, we measured the safety of the aircraft most commonly involved in primary training. In an effort to contain the size of this project, weve limited our investigation to mainstream models, including the Cessna 150/152, Cessna 172, Piper 140, Warrior and Tomahawk and, by special mention, the Diamond Katana, the only honestly new thing in flight training for the past two decades. Right up front, well tell you the winners: The Cessna 172 and the Katana. The venerable Cessna 172 has all the desired attributes of a good trainer but few of the faults and theres little doubt that it has faced the rigors of the crash-and-dash world of flight training and rarely been found wanting.

Considering that nearly 25,000 of all types are flying, the Cessna 172 may be the most risk-exposed airplane in the GA fleet. But more on that later. The Katana hasnt been afield as long but in its short history, it has done remarkably – yes, exceptionally – well at keeping pilots out of trouble and keeping them alive when they cross the line into uncontrolled flight.

How We Did This
As we noted time and again, aircraft safety comparisons are fraught with potential errors, traps and rabbit holes. Finding out about accidents is easy enough. In fact, now that the NTSB has a detailed and searchable Web site, its easier than ever.

Accuracy is a troubling issue, however, since the NTSB still miscodes data and misidentifies aircraft make and model occasionally. Further, we know by direct experience that some accidents never make it into the NTSB database. We can only hope that these oversights apply equally to all types and models. (For example, due to miscoding, it took some digging to find the U.S. Katana accidents.)

Were even less confident about the other critical element of the safety equation: The accident rate. In order to quantify apparent risk, the level of exposure must be known and this is traditionally given as units composed of 100,000 hours of flight time. A great idea in concept, not so great in the real world.

No one keeps accurate tally of GA flight hours by type, although the fleet total is estimated by both the FAA and the NTSB. The FAA last took a weak stab at hours flown through the use of its annual avionics surveys but these are of questionable accuracy and havent been done in more than five years.

For our accident rate estimates, we used two methods. First, we used the estimated hours flown by each model given in the Aircraft Bluebook Price Digest which, given the paucity of data in general, are accurate enough for our purposes here, in our view. But make no mistake, were sure theres a substantial margin of error; lacking reliable hours-flown data, we simply dont know what it is.

Second, we established a ratio between the number of accidents for each model and the number of those models carried in the FAA registry. Crude yes, but a reality check against what may be erroneous hours-flown totals. It stands to reason that if one model has the same number of stall/spin accidents as another model but far fewer exist in the FAA registry, thats a good indicator of relative risk.

For this safety study, we looked at accidents which occurred during the six-year period between 1993 and 1998, for which final NTSB accident reports are generally available. For the Katana, we used 1995 to 2000, checking both NTSB data and information provided by the manufacturer. In raw numbers, our actual rates dont necessarily match those done by other groups, such as AOPAs Air Safety Foundation because of variable model selection and flight hours calculations. But as we see it, the absolute rates are less critical than relative rates between models using the same methodology.

Accidents of a Type
If weve learned anything from years of poring, bleary-eyed, over NTSB accident reports, its this: Although theyre endlessly creative, pilots have only so many ways to prang airplanes. When fishing for the big numbers, accident categories break down into about 10 broad classifications, which weve listed in our charts. By far the leading cause – or should we say result – of training accidents is loss of control on the runway, following a bounce, a wing ding or loss of directional control. These usually terminate in the weeds short of the runway or off the overrun or amongst the hapless tiedown customers alongside the taxiways. They are rarely fatal but occasionally result in minor injuries.

Fully one-third – and a bit more for some models – off all light aircraft accidents fit into this category. Even among non-training aircraft, runway loss of control leads the list of accident causes.

Next up, it gets more complicated. For some models, the second leading cause is fuel exhaustion while for others its engine failures or engine-related incidents. But this varies widely. For example, only 7 percent of Cessna 172 accidents were caused by fuel exhaustion while 12 percent of Piper Warrior wrecks occurred after the pilot ran the tanks dry.

Although pilots seem to make sport of running out of gas, they dont kill themselves very often doing it. On average, fuel exhaustion accidents are fatal less than 10 percent of the time, although injuries from the minor to the serious are more common.

The significant killer in trainer accidents – at least expressed as a survival percentage – is VFR-into-IMC encounters. For obvious reasons, these almost always result in the loss of the aircraft and more than half of the time, they prove fatal to some or all the occupants.

Our research doesnt reveal any typical VFR-into-IMC scenario but there are common threads. One is the student pilot who ventures off on a marginal day, encounters weather and loses control of the airplane. Another is the freshly minted private pilot, sans instrument rating, who launches off on a trip, perhaps with the family aboard, and gets into both weather and trouble.

On a percentage basis, Cessna 172 VFR-into-IMC accidents dont appear any more or less fatal then among other types, but because they have more seats to fill and greater payload, the number of casualties tends to be higher.

This sheds some interesting light on the way in which airplanes are flown affects their accident rate. In pure trainer service, VFR-into-IMC accidents tend to be few because theyre rarely flown in bad weather and if the encounter is inadvertent, the instructor is usually instrument rated and able to handle it. That sort of incident never makes it into the NTSBs files. Thats evidently why VFR-into-IMC encounters account for a small percentage of Cessna 150/152 accidents. But Cessna 172s do both trainer duty and service as cross-country machines, so their exposure to VFR-into-IMC is greater.

Engine, Fuel
Fuel exhaustion continues to plague pilots at all levels of experience, including student and instructors flying trainers. Why this is so is one of the great puzzles of aviation training, since the FAA, flight schools and publications have written about the topic ad nauseam.

The typical fuel exhaustion accident? Engine stoppage and forced landing followed by a round of denial and insistence by the pilot that he had enough gas and that something must have gone wrong.

Usually it did, in the form of poor planning aided and abetted by strong winds and a failure to grasp the concept of leaning. What amazes us is the number of fuel exhaustion accidents that terminate a mere mile or two from the intended destination airport.

One of the more interesting findings in crunching this much data is the number of engine failures not related to fuel exhaustion or fuel contamination. These ranged from a low of 5 percent for the Piper Tomahawk to a high of 21 and 22 percent for the Piper Cherokee 140 and Warrior series respectively. You read that right: One in five of the 180 Cherokee 140 accidents we reviewed between 1993 and 1998 involved engine failures.

Not especially good odds, in our view, and food for thought when youre motoring over the Alleghenies at night in a rainstorm. The 140s stablemate, the Lycoming-powered Warrior, had a similarly poor engine reliability record, with cases of cylinder or valve-related engine failure.

What, exactly, is going on here? Worth noting is that a half-dozen of the 38 engine failure accidents we found were unknowns, suggesting possible carburetor icing or even poorly described fuel exhaustion.

Then again, with no reliable data to confirm them one way or another, who knows? But 28 were bona fide mechanical failures related to defective or failed parts or poor maintenance. Ten involved failure of a cylinder or exhaust valve, a pattern we didnt see in the other trainers, including those with Lycoming engines. (Only the Cessna 150 has a Continental engine.)

The Cherokee 140 has an odd landing light design with a gasket that can come loose and block the engines induction inlet. This has happened more than once. Last, three of the stoppages were caused by oil line ruptures or leaks.

Our advice: To improve the Cherokees engine reliability – especially those troublesome exhaust valves – change the oil frequently, lean aggressively and take valve wear inspection checks seriously. The trainer with the best engine reliability record was the Diamond Katana, with only two engine failures, one of which was operator induced by lack of oil. As noted in the sidebar, however, the Katanas population is too small to represent a fair comparison to either the Cessna 172 or the 150/152 series.

Carb Icing
When Cessna got back into the piston aircraft business in 1997, one of the many changes it made in the 172 and later the 182 was the elimination of carburetion in favor of fuel injection, the theory being that if there was no carburetor, there could be no carburetor icing. Our review of the Cessna 172Rs accident records suggest that Cessna was right on this count but taking the global view here, was carb icing really that big a problem in the older models? We dont think it was.

In the 172, for example, of 972 accidents between 1993 and 1998, 2 percent appeared to be caused by carburetor icing, although the true number may be higher because some accident reports cite unknown causes for engine failures. These may or may not be carburetor icing.

As should be expected, the 150/152 fared much worse in this regard, with 5 percent of accidents caused by carburetor icing. Why would we expect it to be worse? The 172 is a dual-purpose machine, being used for both training and as an entry-level cruiser while the 150/152 is more devoted to pure training, thus its likely to spend more of its flight hours poking along at lower power settings or idle power, where carburetor icing is more likely.

What surprised us is how often carb icing turns up as a cause among airplanes where its traditionally not expected: Cherokees. In the Cherokee 140 and Warrior, carb icing appeared to be an accident cause in 2 to 3 percent of all the wrecks listed or about the same rate posted by the Cessna 172, a model known for its propensity to ice. Even the Tomahawk had a worse carburetor icing history than the Skyhawk.

Stalls and Spins
The flight training edifice has erected a veritable shrine to the task of stall/spin avoidance training, considering the flight time the typical student devotes to stall recognition and recovery. Does the training pay?

In our estimation, it probably does, since the classic stall/spin scenario isnt much of an accident factor when looked at globally. The manufacturers deserve some credit for this as well because although the trainers we examined here may not qualify as spin resistant they also arent especially spin prone. Spin prone means a tendency to easily enter into an inadvertent spin following a stall, not difficulty in recovering from a spin or a tendency to flatten.

Pipers PA-38 Tomahawk has a reputation for poor stall/spin characteristics but our review of the accident data suggests, surprisingly, that its not much worse in this regard than any of the Cessnas or the Cherokees.

Since the fleet sizes vary so markedly – there are a total of about 35,000 Cessna 150/152/172s in the fleet versus only 1200 or so Tomahawks – so does the potential exposure. In any case, stall/spins accounted for 4 percent of Tomahawk accidents, versus 3 percent of Cessna 172 and Cessna 150/152 accidents.

But thats not to suggest the Tomahawk has been unfairly maligned. When the accident review is expanded to include stall/mush incidents, the Tomahawk does noticeably worse than any other model, with some 15 percent of all accidents the result of stall/mush or sink. When stall/spin and stall mush are rolled together, nearly one in five (19 percent) Tomahawk accidents are caused by stall-related factors, which makes it the worst trainer in this regard. The Cherokee 140 runs a close second, with 13 percent of all its accidents caused by stall/spin or stall/mush. By comparison, at about 9 percent, the Cessnas seem to fare better in the stall/spin/mush category.

Tomahawk pilots typically get into trouble after rotation or on a go-around when the airplane is heavy and the density altitude is high. These are usually relatively low-speed, low-altitude encounters with runways and terrain and although they often produce injuries, we didnt find any fatalities caused by stall/mush incidents.

Rates Compared
As we noted, the two big winners are the Cessna 172 and the Diamond Katana. With an overall accident rate of 3.3 per 100,000 hours and a fatal rate of .54 per 100,000 hours, the Skyhawk is hard to beat. The same can be said of the Katana. The Warrior and Cherokee 140 are close seconds but have higher fatal rates.

The Katana has posted impressive safety figures that are probably even better than the 172. We say probably because were certain Diamond knows about and has told us about all Katana accidents. Were just as certain that NTSB figures dont include the entire picture for the 172 simply because of sheer numbers. Who knows how many accidents simply arent reported?

Pipers trainer workhorses – the Warrior and Cherokee 140 – are nearly the equal of the Skyhawk, but looking deeper reveals some weak points; a tendency toward engine failures as an accident cause and, in the 140, a higher incidence of stall/mush than in the Cessnas.

The Tomahawk has what we consider an awful stall/mush record, with one in five accidents due to that cause, not the spins that its supposedly notorious for getting into.

Finally, the Cessna 150/152 series, the airplanes that have likely taught more pilots to fly than any other type. Again, with their high overall and fatal accident rates, the 172 and Katana are more attractive as safe rides, in our view.

Rarely is safety the only criteria by which to measure a trainer but if that happens to be the case, the Skyhawk and Katana have the best safety record, in our estimation. Neither of the two have potentially nasty habits, an even temperament well borne out in the accident records.

Also With This Article
Click here to view “Rankings by Model.”
Click here to view “The Special Case of the Katana.”
Click here to view “New Skyhawks Are a Work in Progress.”
Click here to view “How Taildragger Trainers Stack Up.”
Click here to view the trainers reviewed.

-by Jane Garvey and Paul Bertorelli

Jane Garvey is a contributing editor and Paul Bertorelli is editor of The Aviation Consumer.


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