February 1, 1991
SETH B. GOLBEY
If asked to speculate, most pilots would probably guess that landing and takeoff accidents account for the bulk of mishaps in conventional-gear (tailwheel) airplanes. They would be correct but would probably be surprised to learn that pilots of tricycle-gear airplanes run afoul of the laws of physics during landing to a greater degree than conventional-gear pilots.
Fueled by that irony, we went looking for more. We gathered, courtesy of the AOPA Air Safety Foundation's Emil Buehler Center for Aviation Safety database, information on 6,968 tricycle-gear and 4,302 conventional-gear single-engine airplane accidents that took place between 1982 and 1988. The causes of the accidents were broadly separated into mechanical/maintenance-related, pilot-related, and other/undetermined. The mechanical set was subgrouped according to aircraft system; the pilot set, by phase of flight. While we did not undertake the rigorous examination of each accident that would be required to draw profound conclusions, we did find a few more surprises and some food for thought.
Our main conclusions were that, first, conventional-gear airplanes experience a significantly higher rate of mechanical/maintenance-related accidents than tricycle-gear airplanes. Particularly noteworthy was the number of accidents resulting from airframe and control system failures in conventional airplanes. Second, we confirmed that, while conventional airplanes suffer relatively more takeoff accidents, tricycle airplanes have a worse record of landing accidents. Third, conventional airplanes have a disproportionately high incidence of accidents while maneuvering at low altitudes. Let's look at the numbers.
The initial statistical comparison of the groups reveals nothing special: 15.7 percent of the tricycle-gear accidents in our study group resulted in fatalities, while 14.3 percent of the conventional-gear accidents did.
While mechanical/maintenance factors accounted for less than 9 percent of accidents in tricycle-gear airplanes, they were involved in more than 15 percent of the conventional-gear accidents. In both groups, almost half of these accidents were attributed to the powerplant/propeller system. For conventional-gear airplanes, the fuel system and the landing gear/brakes/wheel system came in second and third; for tricycle-gear airplanes, that relation was reversed. But where electrical/ignition system and oil system problems just about tied for fourth place in tricycle-gear accidents, control system or airframe failures stood out as the fourth most frequent mechanical cause of accidents in conventional-gear airplanes. In fact, the rate, while admittedly very low, was almost three times higher than for tricycle-gear airplanes.
Turning to pilot-related accident causes, we find that, indeed, landing hard, long, short, or otherwise badly accounted for almost 30 percent of all accidents in tricycle-gear airplanes and almost 23 percent of all accidents in conventional-gear airplanes. Among the "otherwise" part, loss of directional or other control, particularly during crosswind or gusting conditions, was responsible for almost half the landing mishaps in conventional-gear airplanes but only a bit over a quarter of tricycle-gear landing accidents. On the other hand, 30 percent of the landing accidents in tricycle-gear airplanes were attributed to hard landings, but only 12 percent of the conventional-gear landing accidents involved hard landings. Of the hard landing accidents, 22 percent led to gear collapse or failure in tricycle-gear airplanes but only 9 percent in conventional-gear airplanes. Improper flares and botched recoveries from hard landings were other leading causes of hard landing accidents in both groups.
The next most frequent pilot-related accident category was the takeoff and initial climb segment, accounting for just over 13 percent of total tricycle-gear accidents and just over 18 percent of total conventional-gear accidents. Again, loss of directional or other control, especially with crosswind or gusty conditions, was the leading cause of takeoff accidents in both groups, responsible for almost 22 percent of the takeoff accidents in conventional-gear and almost 18 percent of the takeoff accidents in tricycle- gear airplanes. Other significant causes in both groups included poor field conditions, failure to maintain proper airspeed leading to a stall after takeoff, and engine stoppage due to fuel contamination or selection of an empty tank.
The next most frequent pilot-related accident cause in tricycle-gear airplanes was running out of gas — more than 9 percent of all accidents (conventional-gear pilots ran out of gas only half as frequently), but the next most frequent accident scenario for conventional-gear pilots — at an attention-getting 16.6 percent of all accidents — was maneuvering/low-level flight, a regime accounting for only 6 percent of tricycle-gear accidents. And the vast majority of these accidents (almost 43 percent) occurred when a low-flying taildragger collided with obstacles, terrain, or water. Low- altitude stalls, spins, or loss of control, often associated with "buzzing," were also significant causes. The same accident causes were present in similar proportions for tricycle-gear airplanes (e.g., 40 percent of low-level accidents resulted from collision with obstacles, terrain, or water), but in much smaller numbers. (One possible partial explanation for the preponderance of conventional-gear accidents in this category is that conventional airplanes, on average, have a smaller range between normal cruise and stall speeds — which leaves the pilot less margin for error when low and slow.)
One more anomaly: Almost 5 percent of the total tricycle-gear accidents resulted from weather encounters during cruising flight — usually continued VFR flight into deteriorating weather or instrument meteorological conditions. Conventional-gear pilots had only a third as many accidents related to scud-running and other weather factors.
The final category of accident causes — other/undetermined — accounted for just over 9 percent of the tricycle-gear accidents and just under 10 percent of the conventional-gear accidents (there was only 0.4 percent difference between the groups). In both groups, the most frequently cited instance was a power loss that occurred for undetermined reasons.
Some of the "other" accidents can be regarded as highly unusual, sometimes bordering on the bizarre — "fertilizer dust in cockpit ignited," "parachutist fell off wing at altitude too low for chute to open...ground handler caught in banner during pickup...passenger inadvertently opened door, fell out of aircraft," "crashed during unauthorized flight by nonpilot," "aircraft stolen, damaged/sabotaged, off-airport landing, drug related," "improper maneuver by glider pilot caused tow pilot to lose control," and the chilling "aircraft disappeared during flight."
What broad conclusions can be drawn from the accident record? From a mechanical/maintenance standpoint, we might observe that conventional-gear airplanes are, as a group, generally older than tricycle-gear airplanes. While usually mechanically simpler, they are no less dependent on meticulous maintenance as they age. The evidence suggests it is worthwhile to devote extra attention to inspections of conventional-gear airplanes, from preflights to annuals, and to be particularly sensitive to any signals that the engine might be in declining health. Corrosion is of particular concern in older airplanes.
From the occurrences of accidents involving banner and glider towing and crop-dusting, we are reminded that a large proportion of conventional-gear airplanes work for a living, often in less than optimum circumstances from a safety aspect. Moreover, because they are more frequently based at short, rough, soft, or unprepared landing areas, conventional-gear airplanes are often exposed to greater operational risks than many tricycle-gear airplanes.
Clearly, pilot proficiency is of key importance. Although a smaller proportion of accidents in conventional-gear airplanes are pilot-related, compared to tricycle-gear airplanes, the emphasis on proficiency, recurrency training, and development of sound judgment and decision-making skills cannot be overemphasized.
Dr. Jonathan Sackier talks about allergies.
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