The Spiral Dive Conundrum

According to NTSB data, in the first decade of this century, over 40 percent of fixed-wing general aviation fatal accidents occurred because pilots lost control of their airplanes.

I find statistics like these mystifying. Why do people fumble the recovery from loss-of-control situations so often? After giving more than 2,500 hours of instruction, I haven’t noticed any particular trouble with it in training.

Perhaps that’s the problem: circumstances conspire to prevent accurate simulation of the scenario we’re trying to model. I’ve long harbored such suspicions, but could never really put my finger on exactly why. But in this month’s AOPA Pilot, Bruce Landsberg posits a theory that helps connect the dots:

Recovery from spiral dives, as presented in training, seems simple. Distract the trainee; place the aircraft into an incipient dive; have the trainee recover by immediately reducing power, rolling wings level, and returning to a level pitch attitude.

Unfortunately, this does not replicate reality. The trainee is primed to look for an unusual attitude, so distraction is absent. The recovery is started quickly for safety reasons, before the speed becomes a factor, so it’s a “baby” spiral — not its nasty big brother.

It’s difficult to induce vertigo under these circumstances, and true vertigo is a big distraction. In a well-developed spiral, the aircraft will quickly accelerate to well above trim airspeed.

As soon as the aircraft is rolled to level — assuming the pilot gets that far into recovery — it will seek trim speed. If cruise (and trim) airspeed is 150 knots and the pilot manages to get wings level at around 210 knots (and the maneuvering speed is 130 knots), there will be a pitch up as the aircraft seeks to regain trim speed. The pilot must push forward — firmly — to unload the aircraft structure.

Being so far above maneuvering speed, and possibly above redline, it’s not surprising that many inflight breakups follow a spiral. In some cases a trainee is told that since the aircraft is going down, they need to pull up. In a fully developed spiral, that’s exactly the wrong guidance! It’s going to be wings level and a push — if the aircraft continues to climb for a bit, getting away from Mother Earth is a great solution.

You’d think after 7,500 hours I’d have figured this out. But then, I’ve never been 50 or 60 knots beyond redline in a normal category airplane while trimmed for cruise.

As Bruce notes, the spiral dives we simulate in training are not like the ones encountered in real life. They can’t be, because we avoid exceeding Vne at all costs. It profits nobody if we cause an accident while providing the very training necessary to prevent one. Instructors are very much like doctors in that regard: “first, do no harm”.

So what’s the solution? Simulators? Unfortunately, even the most sophisticated Level D boxes — which cost millions (if not tens of millions) of dollars — can’t duplicate the loading a post-Vne spiral dive would generate. It seems to me that if the situation can’t be accurately modeled, we’re in no better of a position than with the baby-spirals we currently use in actual aircraft.

Regardless of where they’re held, these training events already lack the genuine surprise inherent in any real-world upset. When the instructor briefs a spiral dive recovery prior to the flight, you can bet your bottom dollar one might be in the offing.

Most pilots have never even been in a real spiral dive. These things are extremely dangerous. When I teach spins, I make a point of discussing and demonstrating the difference between spins and spiral dives. The primary difference, of course, is that spins are a stalled condition where excessive angle of attack and high drag keep airspeed low and stable. A spiral dive is an unstalled condition. Airflow over the wing is smooth, drag is low, and as a result the airspeed builds rapidly. Even to aerobatic airplanes, the spiral dive can be a fatally destructive event and I’ve seen people attempt a spin but not reach the critical AOA. The resulting flight path looks like a spin but is not.

Speaking of aerobatic airplanes, the latest trend is to utilize them for upset recovery training. This is a good thing, but spirals are a unique case. Aerobatic aircraft are better able to simulate the forces and sensations involved with a high-speed spiral dive, but the airframes aren’t like the ones we fly in instrument conditions. If you put 6g on an aerobatic aircraft, it won’t complain. The normal category ship, on the other hand, would be well beyond even the 50% safety factor of its 3.8g limit. The acro mount will also, among other things, feature larger and more responsive control surfaces, higher pitch and roll rates, lighter stick forces, and far less stability.

We can talk about a spiral dive all day long, but until you’ve seen one, I’m not sure the odds of recovery in a surprise situation are all that great, especially if vertigo is thrown into the mix.

If someone asked me how to best prepare for a scenario of that ilk, I’d recommend not even trying to simulate it with full fidelity. Instead, I’d suggest 10-12 hours of basic aerobatic training. Familiarity and experience in all-attitude flying goes a long way toward keeping panic at bay, bringing a sense of been-there-done-that to the unexpected. The load factors will be familiar. Higher than normal control pressures and/or deflections required for recovery will be as well. And most of all, staving off tunnel vision may allow the wayward pilot to recognize the increasing airspeed and figure out what’s happening before it’s too late.

It’s not a perfect answer, but at the moment it might be the best we’ve got.

  8 comments for “The Spiral Dive Conundrum

  1. June 8, 2015 at 6:25 am

    I know technology solutions are unpopular given all the focus these days on returning to stick and rudder skills, but I’d like to know if the Garmin blue-button would command a safe recovery from a fully-developed spiral dive.

    • June 8, 2015 at 10:12 am

      Good question. I’ve always been impressed with Garmin autopilots. But any autopilot is only going to be as strong as the servos which physically power the flight controls. The GSA 28 which ships with G3X systems, for example, has a max torque setting which is configurable between 10 and 60 inch-pounds. It determines when the electronic slip clutch will begin to slip. This is so the pilot can overpower the AP if needed. While the level button is useful for some situations, I doubt it could recover from a high speed spiral dive without allowing the sort of destructive loading on the airframe that Landsberg was referencing. I could be wrong, of course, but based on my understanding of autopilot servo speed and toque limits, I wouldn’t put too much faith in it resolving a situation of this type.

  2. David
    June 8, 2015 at 10:15 am

    When I was in the US in 2014, doing my private-comercial, and even though I had a 1000hrs in Chile, the way they teach stalls is fine, but it seemed to me that I was being taught the perfect way to enter a stall and the perfect technique to exit it. Now even though this is probably a good way to teach someone who has never flown before and to try and ingrain the procedure of how to exit the stall, it seemed to be very programmed and the criticism seemed to be on doing exactly the maneuver that the instructor wanted, I guess that what I am getting at is that a spin or two would have been a better use of a students time, than endlessly repeating stalls. A spin really gets your attention, especially the first time, you really start to then appreciate how fast a plane can get away from you. I usually try and at least give my students one or two examples and then have them recover from one, its not in the program or on the exam…but I find that a demonstration at least doesn’t shortchange them.

    • June 9, 2015 at 1:00 am

      I suspect that the exacting way you were taught to perform stalls has to do with the fact that the Practical Test Standards lay out specific metrics for examiners to use in judging the maneuver. In other words, they wanted you to do them that way because that’s what you needed to do to pass the test.

      Did that make for the most valuable possible learning experience for you? Probably not. There’s always a conflict between teaching things the way they’ll need to be done on the practical test and exposing students to real-world scenarios. We try to combine the two, but as you noted, it’s not always easy or even possible.

      The problem is made worse by the high — and rising — cost of flying. As you probably know, instructors are under ever greater pressure to maximize the progress made for every hour of flying, because to do any less is to risk losing that student to the infamous 80% drop out rate. Talk about being caught between a rock and a hard place!

  3. June 8, 2015 at 12:54 pm

    Would a safe way to teach a spiral dive be to show the symptoms leading to it? Strikes me a pilot should be recovered from a spiral dive, spin, stall or whatever, before they are even in it.

    • June 8, 2015 at 1:43 pm

      Absolutely. An ounce of prevention is worth a pound of cure, as they say. The goal is to avoid unintentionally getting into any of those situations in the first place.

      You caught an important point with that last sentence: spins, stalls, spiral dives, and other abnormal situations needn’t be deadly if they’re caught and counteracted early on. The longer they are allowed to continue, the worse things get. The spin more fully develops, the stall loses more altitude, the spiral dive builds more and more airspeed.

      Prevention is the most desirable option. But it’s human nature to fear the unknown, and pilots flying around without practical exposure to spins and spiral dives are probably not terribly comfortable with the idea of dealing with one.

  4. June 8, 2015 at 2:28 pm

    One habit that served me well thus far was: if airspeed grows, idle the power. This conviction may be strong enough to overcome the vertigo, although that is to be proven yet (the vertigo I had so far all was of a rolling variety, making me to bank the airplane, but not forcing elevator movements). The result is that many instructors are not impressed with my stall recovery technique, but it served me well outside of the lessons.

    • June 9, 2015 at 12:48 am

      You’d think it would be intuitive to minimize engine power if the airspeed was rapidly increasing, but in real-world situations, the surprise, confusion, fixation, and/or paralysis that we find so difficult to simulate in training can make even the most basic tasks nearly impossible.

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