Technique: The Accidental Stall

Has it happened to you?

August 1, 2008

The Piper Cherokee 140 was airborne, but it wasn’t happy. In ground effect all had seemed normal; symptoms only began appearing when the aircraft tried to climb. Any attempt to pitch up to a normal climb attitude was greeted by the flickering of the stall-warning light on the panel, and then buffeting. Efforts to accelerate by reducing pitch threatened to give back the precious few feet of altitude that had been gained.

Ahead, off the end of the disappearing runway, sat a small open-air restaurant. Its roof peak had never seemed this high before. The choices all seemed to add up to the same thing: pull the nose up and stall the aircraft onto the ground somewhere in the vicinity of that building. Push the nose down, idle power, and fly the aircraft onto the ground in about the same place. Not the way this flight lesson with a student pilot, her instructor, and her backseat-riding husband was supposed to begin.

The situation made no sense to the CFI, who had taken over flying and was busily scanning gauges for signs of trouble. Engine rpm was strong, the mags were on Both, and the flap configuration correct. Center of gravity and weight had been computed when the husband—owner of the aircraft—decided to ride along, but was within limits thanks to a partial fuel load. Fuel gauges: unreliable as usual, disregard. It was a warmish summer day but not too bad from a density altitude point of view. Still the airplane, never exactly a spritely performer but capable of this flight, behaved as if it had left the ground with iced-up wings.

As the picnic tables outside the seafood joint came into clear focus, acceleration began to show on the airspeed indicator. Ever so gently, it was possible to coax the ship up into a slight climb without reawakening the stall. Don’t try and turn just yet—just fly it out over the bay and be thankful for the lack of obstacles ahead. Apologies to the tourists munching their seafood baskets below, but, as the crew of a distressed Apollo moon mission famously commented, “We’ve got a problem....”

Turns out that the airplane’s disagreeable behavior had a simple cause, discovered in the subsequent debriefing. During the few minutes after the preflight inspection, while the instructor had walked back to the office to find a headset for the backseat-riding spouse, said spouse decided on impulse to top off the Piper’s fuel tanks from gas cans in his vehicle. The flight had gone out heavy.

Here’s something else you gotta believe: Had that aircraft fully stalled during takeoff, it would have had no resemblance to the departure stall scenarios that show up in conventional flight training or on checkrides. This was a sneaky setup—nothing like the grandiose, nose-high, power-on, barrel-over-the falls departure stalls students come to loathe during training. That’s one of the most dangerous facts about the accidental stall: it can be a stealthy thing, devoid of the usual aeronautical melodrama, the white-knuckled waiting, the big break, the dramatic down-pitching recovery.

Although this stall never got further along than the incipient stage, recovery could not be performed to mimic the assertive methods introduced during training. The envelope for successful recovery was that very thin slice of performance available that preserved most of the altitude achieved while still gaining some needed knots. And a word about stall-warning systems: what kind does your aircraft employ? An aural stall warning, rather than a tiny light might have saved a few seconds. That flickering light, only spotted in the corner of an eye, might have been missed until buffeting announced that it was too late.

If the accidental stall entry has a different personality than the typical training stall, its close relative, the accidental spin entry, can be equally hard to recognize. And considering that only flight instructor candidates, and pilots who opt for aerobatic or upset training, get polite introductions to spins, that’s food for thought for everyone else.

A choppy day provided a delicious opportunity to take Chuck—not the smoothest of pilots, with his stubborn tendency to over control—out to the practice area for some work on flight at minimum controllable airspeed. He wasn’t doing a bad job, bouncing along upwind at a groundspeed equal to that of the school buses visible below, except that his aileron inputs were rarely matched with coordinating stabs of rudder. An ATC call pointing out pop-up traffic demanded the flight instructor’s attention to starboard when a severe jolt banked and pitched the Cessna 152.

Never fear, Chuck was on the case! But his enthusiastic but uncoordinated aileron input just as the stall break occurred made a nice job of his first spin entry. Recovery from an incipient spin induced by turbulence and clumsiness under partial power has a different set of demands than when a more traditional list of ingredients are baked into the recipe by the pilot. Here too, don’t underestimate the surprise factor, and its effect of briefly inhibiting a correct diagnosis of the situation.

There must be many pilots out there who have come close to an accidental stall and don’t even know it happened to them. Any pilot who has ever made a casual estimate of a center of gravity position after loading, only to find the aircraft pitching up too much and too soon on takeoff, may have been a mere inch or two of CG moment arm away from an uncontrollable situation. There are other ways to come close to the edge. I have seen a pilot turn around to check on rear-seat passengers (or even attempt to calm a quarrelsome child) during a takeoff climb while still clutching the yoke, bringing the nose dangerously high and airspeed almost critically low. Ignoring nose-up trim and then adding abrupt, full power on a touch-and-go or a go-around can set the horn squawking and challenge a pilot to muscle the aircraft back into controlled flight.

Diverting a Cessna 172 to the nearest airport after an encounter with unforecast freezing rain seemed like a learning opportunity as the instrument student pilot lined up for his straight-in visual approach to Runway 35 in Manchester, New Hampshire (MHT) years ago. The goal was simple: keep your speed well up and make a no-flaps landing because there’s no telling what this thin, rough glaze of ice is doing to our wing. Readiness did not preclude a surprise when buffeting kicked in, at perhaps twice VS. That’s when you land fast and give silent thanks for that long runway ahead.

Focus here has been on how accidental stalls can bear no resemblance to traditional training stalls. But even the conventional stall has surprises. Raise the nose too much or relax mentally too soon during recovery from the stall entry that you have practiced (it is hoped) dozens of times and you could meet the secondary stall, often possessing all the surprise value and unpredictability of other accidental stalls.

Transitioning from a power-off stall recovery to a power-on spin entry, thanks to a surprise secondary stall, doesn’t add to a pilot’s confidence, but it is educational. Avoid the secondary stall by striking careful balance, on one hand observing the Practical Test Standards requirement to recover with a “minimum loss of altitude appropriate for the airplane” but on the other, not rushing.

Obviously most inadvertent stalls that become causal factors in mishaps start with sharp pull-ups on showboat takeoffs, or departing controlled flight during low-level maneuvering. Inadvertent is a better term for these stalls than accidental because a certain acceptance or defiance of risk is present. An accidental stall, conversely, usually has as its root cause distraction or an aerodynamic surprise (airframe ice, CG or loading errors, and turbulence to name a few).

Yes, there’s overlap between the two. That’s observable when a careful pilot is seduced by acquired overconfidence born of trimming the margins ever closer to the edge. He abandons caution when executing tricky maneuvers required in legitimate low-altitude operations. It’s spooky to see this pattern develop in someone you know, and it gets spookier when the pilot dismisses your distaste for it. Another overlap is the scenario of the cross-controlled stall that occurs when pilots resort to drastic measures to avoid overshooting a base-to-final turn on approach. It’s accidental—but it’s also inadvertent in that the control inputs are a reaction to a developing problem that should have sounded a different kind of alarm in the pilot’s brain.

Dan Namowitz is a pilot and flight instructor living in Maine.

Dan Namowitz

Dan Namowitz | Aviation Writer

Dan Namowitz is an aviation writer and flight instructor. He has been a pilot since 1985 and an instructor since 1990.