Probable Cause #66: If I Had A Hammer

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By Joseph E. Burnside | November 10, 2008

This article originally appeared in Aviation Safety, Aug. 2006.

Probable Cause

There's an old saying: "When the only tool you have is a hammer, everything looks like a nail." In other words, when resources are few, people tend to use the only ones available to them, even if they're inappropriate and have the potential to create as many problems as they solve. Just as it is in carpentry, so it is in aviation. For example, you wouldn't use a Learjet for aerial application work. And a fixed-gear, wheel-equipped airplane is only good for one water landing -- the ensuing takeoff attempt won't be successful. Some readers have visited grief upon me for suggesting in these pages that a lower-powered airplane isn't a good choice for serious cross-country flying. My opinion was forged several years ago after finding a 160-hp Skyhawk that wouldn't maintain altitude in a relatively benign mountain-wave condition. Since then, I've sat on the ground for an extra day while ferrying similar airplanes, waiting for strong winds over mountains to subside. Even when flying better-equipped, more-powerful rides, I've postponed and canceled flights because I didn't think the airplane was up to the task. Sometimes, the pilot isn't up to the task either, but that's another story for another day. To me, the bottom line is that the pilot must decide whether the airplane is capable of handling the planned flight. When the weather's good, the load is light and the terrain is hospitable, even the least-capable airplane might be OK. But add in one or two operational challenges, and things can get out of hand quickly. Here's one example.

Background

Cessna 172

On Aug. 9, 2004, at approximately 1715 Mountain time, a Cessna 172P was destroyed when it impacted mountainous terrain while maneuvering near Monarch Pass, Monarch Crest, Colo. A post-crash fire ensued. Both pilots aboard were fatally injured. Visual conditions prevailed for the cross-country flight, which originated at Montrose, Colo., at 1525, and was en route to McCook, Neb. The airplane and its two pilots were based in the Pittsburgh, Penn., area. Two tourists, hiking near the Continental Divide, heard an airplane approaching. One of the tourists turned and saw an airplane "at eye level, maybe 100 yards away, coming towards me. Then the plane seemed stationary in flight, the engine skipped, [the airplane] took a hard right-hand turn, as I faced the plane, then the tail went straight up over the wing and it went straight down. Instantly into flames." The other tourist saw the airplane "come up [the] mountain [pass], [it] tried to turn around and went straight down." One of the tourists hitched a ride to a nearby ski resort to report the accident. Weather data recorded by the Salida Mountain remote AWOS facility (MYP), approximately one mile east of the accident site, at 1711 local time included calm winds, clear skies and a temperature of 17 degrees C. The altimeter setting was 30.79 inches of mercury. At 1755 local time, weather observed at the Gunnison Airport (GUC) AWOS, 20 miles west of the accident site, included wind from 320 degrees at 16 knots with gusts to 20 knots, clear skies, a temperature of 27 degrees C and an altimeter setting of 30.39 inches of mercury. The accident site was located at 38 degrees, 29.925 minutes north latitude and 106 degrees, 20.347 minutes west longitude. Terrain at the accident site has an elevation of 11,418 feet msl. The Continental Divide's summit, toward which the airplane was flying, is at an elevation of 11,530 feet msl.

Investigation

Sectional chart of vicinity of accident site.

The airplane was aligned on a magnetic heading of 114 degrees, and impacted perpendicular to the mountain. From the airplane, the uphill and downhill slopes measured +24 degrees (45 percent) and -37 degrees (75 percent), respectively. All major components of the airplane were accounted for at the accident site. The descending propeller blade was bent slightly forward, and the ascending blade was twisted and curled aft. Both blades bore 90-degree chordwise scratches on the cambered surfaces, particularly at the tips. Flight-control continuity was established. The flap actuator was not extended. The elevator trim actuator was extended 1.1 inches, which equates to the flaps being up and the elevator trim being five degrees tab down (elevator up). Using the weather observed at the MYP remote AWOS facility, the density altitude was computed to be an estimated 14,300 feet msl. According to the 1984 Cessna 172P Skyhawk "Information Manual," the airplane's service ceiling is 13,000 feet.

Probable Cause

The National Transportation Safety Board determined the probable cause(s) of this accident to include "the pilot's failure to maintain airspeed which resulted in a stall, and his decision to conduct flight beyond the performance capability of the aircraft. A contributing factor was the high density altitude, and an inadvertent stall." Cessna's Model 172 is a great airplane and celebrated its 50th anniversary in 2006. But -- just like any other airplane -- it has its limitations. When one flies an airplane beyond its limitations, one becomes a test pilot. In this instance, the two pilots had coaxed their Skyhawk to a density altitude some 10 percent above its service ceiling, defined as the altitude at which the airplane's rate of climb is at or below 100 fpm, even though the altimeter would have read almost 1500 feet less. The trip being flown by the two pilots had them covering a great deal of territory over a short time and visiting several high-altitude airports. But the two were, essentially, flat-land pilots who, perhaps until this trip, had never dealt with high density-altitude flight operations. It's likely they had never had a Skyhawk at or near its service ceiling. Some of my most memorable flights -- the good and the bad kind -- have involved Skyhawks. And I wouldn't hesitate to jump in one tomorrow, all things being equal. But it's not a good airplane for heavy, high and hot work, or for long cross-countries. Before launching into the wild blue yonder, take a moment to consider whether the airplane you're planning to use is the correct tool to use for the planned flight.
More accident analyses are available in AVweb's Probable Cause Index. And for monthly articles about safety, including accident reports like this one, subscribe to AVweb's sister publication, Aviation Safety.

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