Stall/spin and ground reference maneuvers

I agree, there are multiple inputs to the pilot. The trick is prioritizing them and not getting distracted. I'm probably not any better at it than you; it's more likely that my instructors taught me somewhat differently.

On downwind I concentrate on airspeed, variometer rate, and traffic scan (I'll note the position of the runway as part of my traffic scan). When the runway disappears I'll wait an appropriate amount of time (judged from how fast I moved down the runway), take a quick look for traffic, runway position and turn roll out reference, and then (and only then) initiate my turn to base. During the 5 seconds I'm turning I'm looking directly forward over the nose, paying attention only to airspeed, yaw string and bank angle. The bank angle I always try to use is 45 degrees, while auxiliary inputs are slipstream noise, one or two glances at the ASI, the appearance of the rollout reference, and the imagined voice of my instructor chanting "airspeed, yaw string" over and over.

On the base leg I again concentrate on airspeed, variometer rate, and traffic scan (again noting the runway position as part of my traffic scan). At the appropriate position (judged from how fast the runway extended centerline is approaching, I initiate my turn to final. During the 5 seconds I'm turning I'm again looking directly forward over the nose, paying attention only to airspeed, yaw string and bank angle. Again the bank angle I always try to use is 45 degrees, while auxiliary inputs are slipstream noise, one or two glances at the ASI, the appearance of the runway, and the imagined voice of my instructor chanting "airspeed, yaw string" over and over.

Until a few months ago when I read about "pivot height" on this board, I had never known that the wing tip direction could reverse direction during a turn depending on your height. I assure you that's not from lack of experience on my part, it's just that I never look at the ground when I'm low and turning.

I also agree with you that the numbers of stall/spin accidents are appalling. As a community we need to try to reduce them. I just don't know if making people aware of peripheral vision changes is the way forward. Isn't it better to get them to focus only on what matters for the few seconds that are needed in a low altitude turn?

-John, Q3

On Tuesday, March 4, 2014 9:54:01 AM UTC-5, wrote:
On Tuesday, March 4, 2014 5:34:09 AM UTC-8, John Carlyle wrote:

Just because you perceive something doesn't mean that you have to pay attention to it. The most important things in a pattern turn (or low altitude thermalling) are perfectly coordinated turns and proper airspeed. Scans for traffic and feeling for lift are fine, but who cares what the ground does?



One does look at the airport when initiating the turn from base to final, but once the turn starts all you need to do for the next 5 seconds is look over the nose for pitch, yaw and bank. The airport will appear when you need it without having to search for it.



Well, it's a human in the loop feedback control system with multiple inputs - visual, inertial and some auditory. If you are making a low turn from base to final you may initiate the turn while looking away from the yaw string and airspeed because the runway is off to the side and you are trying to set a turn rate to put you in-line with the runway on final. At the same time your peripheral vision at this altitude is now subtly telling you that you are over-banked/under-ruddered because you are below the pivotal height where the turning cues of the wing against the background reverse. You aren't used to this peripheral cue and may not be aware of how it affects your overall perception of attitude and coordination and how that feeds back into the control system.

You may be better at it than I am, but I can't just take a snapshot to the side before initiating the turn to final and then look ahead to the yaw string and airspeed without ever looking out to the runway again and expect to end up both pointed at and in-line with the runway heading. I tend to scan back and forth. It only takes a moment of being over-ruddered to generate a spin, particularly if you are at low speed (and an approach into an airport in a mountain valley can make you fly too nose-high if you are not paying proper attention).

Is any of this good and proper airmanship - well no. But that is a little beside the point. The fact is that over the past 20 years 39% of fatal glider accidents and 36% of all glider fatalities have been due to stall/spin. That's 43 dead glider pilots and passengers, or slightly more than two per year. It is the leading cause of death while flying gliders. We must be doing something (or some things) wrong. My thought is if we are all aware that our perception from peripheral vision changes (and which way those changes work) we all may be in a slightly better position to resist the subconscious urge to do the wrong thing at just the wrong time.

9B