Aftermath: Basic Mistakes
The owner of the float-equipped Maule saw it crash. He was there to watch as his friend and a passenger arrived in the airplane. “I witnessed the airplane fly over the field,” he wrote, “and enter a downwind for a landing on Runway 4. As the plane turned from base to final, it banked at a very steep angle (est 75 degrees) and then continued to bank even steeper then went vertical from 50-60 feet altitude and within a second impacted, exploded and burned.”
The 42-year-old, 1,300-hour commercial pilot and his longtime girlfriend both perished in the accident, which the National Transportation Safety Board attributed to “the pilot’s inadequate airspeed and excessive bank angle while maneuvering for landing, which resulted in an aerodynamic stall.”
The scenario of the stall-spin while maneuvering in the traffic pattern is a classic one. It is, and has always been, so common that Leighton Collins devoted many pages to dissecting it in the chapter on “The Dangers of the Air” that he contributed to Stick and Rudder, Wolfgang Langewiesche’s ageless 1944 book on the art of flying. Collins gave a lot of attention to the misuse of the rudder, a control that played a larger role in 1944 than it does today. The rudder may or may not have had anything to do with the fate of this particular Maule — the GPS, which stores altitude, speed and ground track, does not, of course, reveal whether or not an airplane is in coordinated flight — but the mere shape of the ground track, and the testimony of several witnesses, provides sufficient evidence of the sequence of causes that led to the accident.
The pilot had approached the area from the east, first overflying the 2,000-foot turf runway and continuing some distance past it. He then turned back, crossing midfield, and making a left 270 onto the downwind leg. The second, west-to-east crossing of the field was at 860 feet above the ground, but the Maule began descending during the turn to the downwind. By the time it was established on the downwind leg, it was at just 310 feet agl.
Since a traffic pattern is normally flown at 1,000 feet above the runway, a pilot becomes accustomed to a certain relationship between wing, horizon and runway on the downwind leg: The line of sight from airplane to runway is so-and-so many degrees below the horizontal. If the airplane is very low on the downwind, an attempt to maintain that accustomed angle, or anything close to it, results in a downwind leg much closer to the runway than normal.
Regardless of altitude, however, the airplane will require the same amount of room to make the turns from downwind to final. When the Maule passed the approach end of Runway 4, it was about 700 feet laterally from the centerline. Its published stalling speed with full flap is 45 knots, which sounds conservative for an airplane with a gross-weight wing loading of less than 15 pounds per square foot. Assuming a pattern speed of 1.3 times the stalling speed — 59 knots — and 30-degree banked turns, a semicircular turn from downwind to final would require a little more than 1,000 feet. If you spent 10 seconds wings-level on base checking for traffic, your complete turn from downwind to final would use up 2,000 feet — about three times the space the pilot had given himself.
The witness report of a 75-degree bank angle prior to the stall has to be viewed skeptically. It’s difficult to judge the bank angle of a turning airplane, and 75 degrees is practically indistinguishable from vertical. It would be sufficient for an airplane to bank 45 degrees in the traffic pattern for it to look very steeply banked indeed.
According to the GPS record, the pilot began the downwind leg with a groundspeed of 48 knots. Of course, groundspeed and airspeed are not the same thing, but the fact that the downwind groundspeed was very close to the stalling speed implies that there cannot have been much wind.