Aftermath: Turbulence Encounter

Rough air was forecast, but the result wasn't.

Aftermath Artwork

Aftermath Artwork

Winter storms approach southern California from the Gulf of Alaska, the low center descending off the Pacific coast and then swinging inland to spend itself in Arizona and New Mexico. When the low is abeam Los Angeles southwest winds race across the coastal plain, leap over the San Gabriel Mountains and tumble head over heels, like frolicking children, into the desert beyond. Like frolicking children, they sometimes break things.

There was such a storm on the last day of winter in 2011. A Cessna P210N Silver Eagle — a pressurized 210 fitted with a Rolls-Royce turbine engine — left Santa Ana's John Wayne Airport around noon bound for Henderson, Nevada, with the pilot and her two young children aboard. The pilot had self-briefed — she liked to use aviationweather.gov — and had filed an IFR flight plan with a cruising altitude of 15,000 feet, an estimated time en route of 1:15, and three hours of fuel aboard.

Whether she saw the airmet for moderate turbulence and icing that had been issued around 8 o'clock that morning is unknown; most likely she did. About an hour before the flight Los Angeles Center broadcast an advisory warning of moderate to severe turbulence along her route; a second advisory was issued five minutes after takeoff. She may have missed these. Sixteen minutes after takeoff, Norton AFB radar passed on a pilot report of light rime icing at the Centurion's altitude, then 11,000 feet, but did not mention turbulence. The controller then advised all pilots to contact Flight Service for a hazardous weather advisory. Because she was waiting for a clearance to continue her climb, and possibly because she supposed that the weather advisory would repeat what she already knew about the forecast icing and turbulence, she apparently did not contact Flight Service. At any rate she did not leave Norton's frequency.

Norton handed the Centurion off to Joshua Approach, and Joshua issued the clearance to 15,000 feet. A little later the pilot, who reported that she had broken out of the clouds at 13,300 feet, had trouble copying a routing change and explained, after a silence of nearly a minute, that it was because she had encountered moderate turbulence. A couple of minutes later a fragmentary transmission came from the Centurion, and then radar contact was lost. Thirty-two minutes after takeoff, witnesses saw the Centurion descending vertically in a spin. It crashed in rough terrain 2 miles south of the Daggett airport. The wreckage was almost entirely consumed by fire.

Meteorological analysis after the fact suggested the Centurion could have encountered a phenomenon called a hydraulic jump or rotor. It occurs when fast-moving air pouring over a mountain ridge encounters and lifts a slower-moving air mass that tumbles over it like a wave breaking on a beach. Hydraulic jumps are sometimes visible as clear rifts in a mass of clouds; satellite photographs showed such a rift just south of Daggett at the time of the accident.

Despite the freakish and unpredictable weather, the National Transportation Safety Board attributed the accident to “the pilot's decision to conduct the flight into a region of reported moderate to severe turbulence and icing conditions, followed by a loss of airplane control and an aerodynamic spin from which the pilot did not recover.”

It is noteworthy that the pilot, not the weather, gets the blame. ­Controllers were aware that airplanes approaching and leaving Los Angeles had been experiencing “horrible” rides — ATC had begun trying to keep them higher than normal, above FL 200, to avoid the extremely rough air below 16,000 feet — but none of the controllers who handled the Centurion warned the pilot of anything ahead of her more menacing than a 10-mile stretch of “moderate precipitation.” Nor was there a placard on the P210's panel saying “Flight in moderate or greater turbulence is prohibited.”

NTSB report-writers are not required to possess degrees in philosophy, but they sometimes seem to have odd ideas about what constitutes a “cause.” The trouble with blaming pilot decision-making in cases like this is that many pilots were flying that day — there were more than 90 pilot reports of icing, turbulence and mountain wave activity with at least the potential for rotors in a 10-hour period bracketing the accident (and not all pilots who encounter rough air file a pilot report) — and no blame at all attaches to their having made exactly the same decision as the accident pilot did.

At any rate, the airplane did not break up in flight, and so we are left wondering why this particular turbulence encounter ended the way it did.

Evidently the airplane stalled and then spun. People who knew the pilot, including her pilot husband (they were both working on their commercial licenses; she had 1,000 hours, 400 in type), described her as conscientious about her flying and duly cautious about turbulence. But there was no indication that she had aerobatic training, had ever experienced a spin, or had any preparation, other than the rather tame “unusual attitudes” of the private ride, for a really violent upset. In fact, her husband reported that she typically hand-flew only 10 minutes of a flight; the rest of the time she just keyed instructions into the autopilot. She was not unusual; most modern pilots fly this way.

While it's possible that turbulence alone would cause an airplane flying at its maneuvering speed to stall and spin, it's easier to imagine a disoriented and panicking pilot doing so once extreme turbulence had tossed the airplane around. But what seemed to interest the NTSB more than how she got into the spin was why she did not get out of it.

The question itself betrays a certain naiveté. A pilot who normally flies by data entry and who finds herself in a developed spin is not at all likely to recover from it, in part because the experience is so unnatural, disorienting and, frankly, terrifying, and in part because airplanes like the P210 are not expected to spin and are not required to demonstrate spin recovery for certification, and therefore may not possess conventional and cooperative spin-recovery manners.

The NTSB, not satisfied, evidently, that recovery from the spin was unlikely on its face, focused some attention upon a bureaucratic aspect of the accident: the possible interactions of multiple STCs.

The P210 had been extensively modified. In addition to the turbine engine, it had gained three fuel tanks, deice boots and 26 inches of additional wingspan, and had lost a weather radar. The NTSB wondered, not without reason, whether the spinning characteristics of the airplane — unpublished, if not in fact unknown, in the first place — had been affected by significant changes in its moments of inertia, which govern both the way an airplane spins and the amount of aerodynamic correcting force needed to arrest a spin once one has developed.

What interested the NTSB was that the various modifications had been performed at different places and times and under STCs that themselves had been approved by different FAA regions, possibly without reciprocal consultation. There was no requirement that the turbine conversion, which included a supplemental fuel tank in the aft fuselage, demonstrate spin recovery, since there was no requirement that the P210 demonstrate it in the first place. Likewise for the Flint Aero wingspan-extending tip tanks. Implicit in the NTSB's discussion was the idea that the original P210 might, in fact, have been recoverable from a developed spin, the modified airplane with its higher moments of inertia might not, and no one knew or was required to find out.

To focus attention on certification is to overlook the larger context in which the pilot's decision to make the flight can be seen as the natural consequence of a sense that a boot-equipped pressurized turboprop is airplane enough to deal with anything short of severe icing or the heart of a thunderstorm. Many, perhaps most, pilots with that sort of equipment would have taken off that day; aviation would not exist if pilots balked at every possibility of icing or turbulence. We assume that we, and our airplanes, will be up to the challenge when and if it comes. Usually we are, but not always.

This article is based on the NTSB's report of the accident and is intended to bring the issues raised to our readers' attention. It is not intended to judge or to reach any definitive conclusions about the ability or capacity of any person, living or dead, or any aircraft or accessory.

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