Dave Salzman and his wife, Susanne, own D&S Aviation, an on-demand charter operation at Van Nuys Airport in Southern California. One of their popular offerings is called "Shimmering Lights," an hourlong sightseeing flight over the Los Angeles Basin at night.
Last November 12 was one of those rare and pristine evenings when the visibility was so good that it almost hurt the eyes to look that far. Dave Salzman was in command of N1195L, the Grumman Tiger won by David P. Lunt in Sporty’s Pilot Shop’s 1993 sweepstakes. Also on board were Salzman’s passengers, a father and his son for whom this flight was a birthday celebration.
Salzman had been cleared to enter a left traffic pattern for Runway 16L at Van Nuys Airport and was downwind, approaching a point abeam the tower at pattern altitude with the wing flaps retracted. The event happened so suddenly and so quickly that it was over almost as soon as it had begun. It was similar to what it might be like to drive an automobile at high speed from a smooth road directly into a high and perpendicular concrete curb without first having seen it.
"It was as though a cosmic sledgehammer had been swung mightily into the Tiger’s belly," Salzman said. "The jolt was so severe that my left arm, the one holding the control wheel, ached for days.
"And the noise was deafening. It sounded as though a .44-caliber Magnum had been fired in the cockpit," he added.
Strangely, the aircraft did not roll, pitch, or yaw. Nor had there been any noticeable altitude change, just a rapid up-and-down translation.
Salzman first thought that he had been hit from below (possibly by a helicopter) and was the victim of a midair collision. He was immediately concerned about the condition of his landing gear. He quickly called the tower and asked about other traffic. None had been reported. Perhaps, he thought, he had flown into some piece of falling space or aircraft debris.
The 6,000-hour ATP-certificated pilot then noticed that his left wing was buckled. He would learn later that the left wing spar and aileron were permanently deformed, and that the right wing root also was damaged. The jolt was so intense that the left and right aileron counterweights had been sheared from the structure. One fell through the roof of an apartment building and became lodged in the concrete floor; the other was never found.
The adult passenger saw the damaged wing and asked if they would be able to land. The Tiger appeared controllable, and Salzman did his best to assuage his passenger’s obvious and understandable anxiety. They landed safely moments later.
After deplaning, it became obvious that there had not been a midair collision. There were no collision or paint-transfer markings of any kind. Nor was there a report of any other aircraft having been involved in such an encounter.
Adding to these confusing circumstances was that the winds on the ground and aloft were virtually nonexistent, eliminating the possibility of destructive wind shear or turbulence. Also, structural failure was ruled out as a possibility because of the spanwise distribution and extent of damage.
Irrespective of the cause, those who inspected the aircraft were amazed that the airplane held together long enough to be flown to a safe landing. One engineer estimated that the Tiger had been exposed momentarily to 15 positive Gs. Others have re-duced that estimate by half. All agree, however, that the aircraft had been subjected to substantially more Gs than that for which it had been designed.
The mystery began to clear when it was discovered later that the Tiger’s position on the downwind leg of the Van Nuys Airport had been overflown only a moment or two earlier by a FedEx Airbus A–300 on an ILS or visual approach to nearby Burbank-Glendale-Pasadena Airport. The ILS approach to "Burbank" is perpendicular to the runways at Van Nuys, and the glideslope passes 600 to 800 feet above the downwind leg for Van Nuys’ Runway 16L.
It is well known that wingtip vortices descend behind an offending aircraft. Was Salzman’s traumatic experience the result of his having flown through the descending wake generated by the FedEx Airbus? To determine if this might be the case, I contacted George Greene, who is regarded by many of his colleagues as the world’s leading expert in wake turbulence. Greene, who now works for the FAA, was in charge of NASA’s extensive wake-turbulence research project for many years.
Lacking firsthand data and analysis, Greene was understandably reluctant to attribute the incident to wake turbulence. He did, however, describe a classic cross-track penetration of a wingtip vortex as being a startling event characterized by a significant bump and a loud bang. "Such events," he added, "are relatively rare, not nearly as common as follow-on [in-trail] events." The most likely time for a cross-track event is when a departing aircraft lifts off and climbs through the wake created by a heavy jet that had lifted off from a crossing runway.
It may never be known with certainty if Salzman’s experience was the result of a cross-track penetration, but given the dearth of contradictory evidence, it does appear that this was the case. It should serve as another wake-up call to the hazards of wake turbulence.
Related Articles
