Not a member? Join today. Already a member? Please login for an enhanced experience. Login Now
Menu

Margin for errorMargin for error

By David Jack Kenny

Perhaps the most distressing aviation accidents are those where a lapse in judgment or airmanship claims not only the life of the pilot, but those of passengers who had trusted their futures to his or her expertise. To make matters worse, a pilot’s nearest and dearest are among those most likely to extend that trust.

On the morning of July 6, 2014, a 180-horsepower Piper Arrow (PA-28R-180) crashed into a mountainside on the edge of a ravine near Lake Elsinore in Southern California. The ensuing post-crash fire was hot enough that the engine’s accessory gears were found jammed by molten aluminum. Lost in the accident were the 49-year-old, 3,400-hour private pilot and his two sons-in-law, both of whom were anticipating the births of their first children.

No one saw the actual impact, but two witnesses watched the sequence leading up to it and one provided a video recording. They described the airplane as “really, really low” and “extremely low,” respectively, as it completed a turn and started up the hillside. The one closer to the scene saw the Arrow make a hard left turn banked at about 45 degrees; as it did so, he heard the whir of the hydraulic system and saw the landing gear extend. After levelling off it barely cleared the power lines across the street from the parking lot where the witness stood. A plume of smoke arose about five seconds after it passed out of sight. The video footage shows the airplane entering the turn with the gear retracted and rolling out with it extended.

The Piper Arrow was designed with an innovative back-up system to prevent accidental gear-up landings.  A secondary pitot-static mast on the left side of the fuselage captures a combination of airspeed and propwash. When ram pressure drops below a threshold consistent with idle power at an airspeed below 105 mph, the gear deploy automatically. The system can be fooled, most notoriously if the sensor’s ram port ices over. Certain aircraft attitudes such as pitching up too steeply during the climbing portion of a lazy eight can also blank enough airflow to trigger gear extension at cruise power. To prevent this, the system also includes an override lever; while engaged, it disables the back-up extender.

The NTSB investigators concluded that the automatic gear extension activated during the turn, and the additional drag with the gear down degraded the airplane’s performance until it could not outclimb the terrain. Given that there was no rational reason for the pilot to have extended the gear deliberately, and that the design of the selector switch makes it difficult to move accidentally, it seems likely that the back-up extender did deploy, though this would not normally happen in a 45-degree bank at cruise power without an exaggerated nose-up pitch. There’s no question, though, that the rate of climb with the gear down would have been no better than marginal. Its owners find that the 180-hp Arrow offers an attractive compromise between speed and economy, but the aircraft's climb performance is sluggish at best. Loaded with three grown men at a density altitude of about 4,440 feet, it couldn’t have done much more than maintain altitude until it picked its feet back up.

Since automatic extension is accompanied by both the gear horn and the gear-in-transit annunciator on the panel, it’s not clear why the pilot didn’t engage the override. The airplane’s history—and the pilot's own—provide one possible hint. His last medical certificate, obtained about seven weeks before the accident, listed no flight time in the preceding six months. Seven weeks earlier was also about the time he began flying the Arrow again after five years of inactivity, during which time it received an engine overhaul and extensive airframe inspection. After its annual was signed off and the engine broken in, he told a friend that the Arrow was “flying better than ever before.” Whether he took the trouble to refresh his understanding of the airplane’s systems, however, hasn’t been reported.

On occasion, focus on the specifics of the accident chain can draw attention away from the most central issues. In this case, the crucial question isn’t why the gear deployed, but why an experienced pilot chose to take his daughters’ husbands—the fathers of his grandchildren—over the hills at an altitude where even clearing power lines might come into question, and where an unexpected event that would be trivial at altitude could put the aircraft into immediate peril. If there’s any good answer, it’s not obvious.