The Dreaded Final Turn Stall
Early on the morning of June 12th, 2013, a Glasair SH-2F departed Montague airport in California. The purpose of the flight was to familiarize one of the two pilots with the handling characteristics of the aircraft prior to a potential sale. Total flight experience of the two pilots exceeded 7000 hours, however, less than an hour later the inverted wreckage was found in a field by local residents. There were no survivors. The official investigation would cite loss of control while maneuvering as the official cause. How could this have happened?
According to FAA statistics (FAA Safety Briefing June 2014), at least twenty-five percent of fatal general aviation (GA) accidents are the result of a loss of control, which continues to be the leading killer of GA pilots (that's you and me). Is this alarming statistic the result of a lack of training, lack of proficiency, or lack of awareness? In my opinion, it's all three. I still remember the look on my instructor's face and the hesitation in his voice when, about halfway through my private pilot training, I informed him that I wished to learn to recover from a spin. He showed me but I'm sure my grade book had a write-up similar to the phrase we used for USAF student pilots who did things that defied logic: NAFOD (No Apparent Fear of Death). It was not then and is not currently a required part of the private, commercial, or even airline transport pilot certification process. To be an instructor, you only have to receive a logbook signature saying you've recovered from spins left and right. This can be done in the widely used Cessna 172, which will stop spinning as soon as the controls are released. The end result is that many of us have never seen more than sixty degrees of bank or thirty degrees of pitch in an aircraft. We've never explored what happens when you over-bank a final turn and try to push the nose around with rudder or slip in towards a landing while getting too slow because we're fixated on the end of the runway. We've only heard, "Don't stall it in the final turn". Because there is no requirement for in-depth training in these supposedly dangerous areas, there is no flight training and very little academic time devoted to increasing awareness. There is no proficiency at recovering from the extremely unusual attitudes that can result from these excursions. However, your aircraft will be happy to show you these attitudes if you simply get distracted by the radio, another aircraft in the pattern, a checklist, or simply a challenging wind condition. It doesn't take much.
So, what does happen when we over-shoot final because of a tail wind in the final turn or simple miscalculation? Hopefully, the answer is a go-around. The other, unfortunately much too popular answer, is to bank and pull the stick or yoke in an attempt to get the nose tracking back around towards the runway. I'm guilty as charged and have done it, so I'm not throwing stones in a glass house. Our brains quickly rationalize that, "It's not a big overshoot so this won't be a problem". The accident statistics, however, beg to argue. Hopefully, your instructor showed you the over-banking tendency of most aircraft once you get beyond about thirty to forty-five degrees of bank. The aircraft wants to keep on "rolling, rolling, rolling, keep those wingtips rolling." Our little bit of extra bank quickly becomes more than we had planned. The excitement in the crowd begins to build!
Next, we apply back pressure to the stick or yoke in order to bring the nose around more quickly. This increases the angle of attack (AOA) which does increase lift but also dramatically increases drag, causing our airspeed to fall off, decreasing relative wind and further increasing AOA. If you have an AOA gauge, this becomes readily apparent. I wish all aircraft had AOA gauges but that's another subject entirely. What we do have is an airspeed indicator and what we'll notice, if we're paying attention, is that it begins to decrease rapidly as we load the wing. We'll also notice that as we approach the typical light GA aircraft seventeen degree stalling AOA, the airspeed will indicate a good bit higher than the stalls we've practiced in straight and level flight. It may quickly exceed our approach speed. The crowd is giddy with anticipation!
Were we to stall in this condition while in coordinated flight (with that pesky ball centered in the goal posts), we'd have a simple accelerated stall and the nose would pitch forward as it does in level flight. The problem we usually have is that we're either still rolling and slightly out of trim or we attempt to push the nose around with inside rudder, resulting in a skid. Now, we have all the ingredients necessary for the classic final turn spin and the crowd is in a frenzy of anticipation. Here's the testable portion: Stall + Yaw = Spin. Remember that. I won't be giving a test but your airplane might.
The problem with a skidding final turn is the airplane reaction at the stall. The airplane will give you little warning before it pops a surprise on you. Because of the skid, the inside wing will stall first and very rapidly. This, coupled with outside wing's lift, causes our airplane to rapidly roll into the turn. In fact, most of my clients find themselves almost inverted in the time it takes to say "Stall + Yaw = Spin". The nose points down and the windscreen is suddenly filled with nothing but ground. The crowd goes wild and it's complete mayhem. If this had been a real final turn at five hundred or less feet above the ground, our chances of surviving would be somewhere up there with our chances of getting hit by lightning while reclining in the command chair deep inside Cheyenne Mountain. Let's not go there, unless it's at altitude,
in an aerobatic certified airplane with a competent instructor aboard. At that point, it's a learning exercise and actually a lot of fun!
How do we avoid this scenario, thereby keeping our story off the list of unfortunate National Transportation Safety Board statistics? First, let's make a promise to ourselves to always go around if we're going to overshoot. Gas is cheap compared to funerals. If we find ourselves rushed, distracted in the pattern, unsure of the situation, or feeling something is just not right, then go around. Give yourself time and distance to assess the situation. Next, let's pledge to not do anything with our airplanes that they are not built to do. Let's also pledge to not do anything for which we've not been trained. Finally, let's promise ourselves not to do extremely questionable and probably illegal things such as low level impromptu airshows or rapid maneuvering without a few thousand feet of air under us. Our awareness and caution levels need to be at maximum as the distance between us and the ground approaches minimums.