Monday, 19 March 2018
REDUCE STALLS AND SPINS WITH RIGHT-HAND TRAFFIC PATTERNS
Acknowledgements: Rod Machado‘s Aviation Learning Centre (https://rodmachado.com)
(Ed. Note: Thanks to Rod for permitting the use of some of his material as part of our blog!)
“This article isn't about changing the pilot. It's about changing the environment in which a pilot flies to reduce the risk of flight. One is completely unrelated to the other. Everyone knows someone who has stalled and spun when making right-hand patterns. That, however, is irrelevant if stalls and spins occur more often in left-hand patterns.
There are several aviation experiments underway which are attempting to find new and novel ways to reduce stall/spin accidents in the traffic pattern. One of these involves making a 180-degree circle–to–land approach in the hopes of eliminating a skidding turn onto final approach - a turn that could result in a spin should the airplane stall. Since I’ve already written about the impracticality of this idea I’ll say nothing more about it here, but I’m not one to criticise without offering an alternate and perhaps more practical way to reduce stall/spin accidents in the pattern.
My proposal is simple: Make right-hand traffic the standard pattern flown by pilots instead of left-hand traffic as recommended by the FAA. There’s a good “common sense” argument to be made about why flying right-hand patterns is actually safer.
But what about those airports where you can’t fly right traffic because of obstructions, environmental concerns, or noise abatement? Well, if right traffic isn’t practical for some reason, then you don’t fly right traffic. Period. In Spanish, we have a phrase for that: Tough Taco. We can’t always get what we want. All I’m saying is that, should my hypothesis be proven correct, we should make right patterns standard so that pilots will fly right traffic more often.
Let me explain. It turns out that today’s pilots tend to favour power-on approaches rather than power-off approaches. That’s because the FAA does not discourage general aviation pilots from flying small airplanes in a similar way to how airline pilots fly their larger airplanes (i.e., make long shallow stabilized power-on approaches). But flying power-on approaches means that small airplanes will have greater exposure to the left-yawing tendencies associated with torque, P-factor, and propeller slipstream.
As power and angle of attack increase, airplanes that are not properly flown are more likely to skid during left turns to final approach and slip during right turns to final approach. If you’ve cracked even one book on aerodynamics over the past decade, you’ll know that stalls while skidding are more likely to result in a spin than stalls that occur while slipping. Let’s look closer at the details.
Stalling from an Uncoordinated Left Turn onto Final Approach
· When pilots turn onto final approach from a left base leg, they tend to skid the airplane’s nose toward the inside of the turn because of improper control use. How so? Rolling out to the right without the proper use of right rudder yaws the airplane’s nose to the left, toward the inside of the turn. This is a skid.
· If the pilot overshoots the turn and pulls aft on the elevator control to compensate for the overshoot, he’ll have to hold right aileron to prevent the bank from increasing.
Using right aileron in either situation results in adverse yaw, pulling the airplane’s nose toward the inside of the turn. Should the airplane’s wings approach their critical angle of attack, the left wing (the wing inside the turn) will likely stall first, as left yaw pulls the left wing aft and slows it down slightly compared to the right wing. Therefore, its angle of attack is slightly larger than the right wing’s angle of attack. The airplane will roll to the left in the same direction the airplane was turning. The left yaw, in this instance, is exacerbated when power is used for the approach. Both the turn and the stalled left wing are acting in the same direction and often produce a quick spin entry to the left.
On the other hand, stalling and spinning from a right turn onto final approach is much less likely to result in a spin. Let me explain.
Stalling from an Uncoordinated Right Turn onto Final Approach
Turning right onto final approach from a right base leg results in the exact same amount of adverse yaw produced by the ailerons as compared to a left turn onto final approach. Failure to use rudder while rolling level from a right turn or holding left aileron to prevent a bank increase during a turn results in the nose yawing toward the inside of the turn to the right. This is the same skid that we just discussed, except that it occurs to the right, not the left.
The big difference here is how power affects the airplane. The use of power yaws the airplane to the left, especially at high power settings and high angles of attack. Therefore, in a right turn to final approach where the pilot fails to use rudder properly, power pulls the nose to the left.
In this instance:
· Should the airplane stall, it might stall in a right slipping turn where the outside left wing stalls first and the airplane wants to roll opposite to the direction of turn.
· Then again, if the power-induced left yaw and the adverse yaw to the right counteract each other, the airplane might stall in a more coordinated flight condition.
An airplane stalling in either condition is less likely to spin and more likely to simply pitch in a forward/downward direction as it would in a typical stall, without the extreme rolling and yawing motion of a spin entry.
Ultimately, flying a right-hand turn to final is likely to be less lethal for pilots who’ve lost, or never had, any significant degree of proficiency with their rudder pedals. I'm not saying that pilots can't spin out of a right, powered turn to final approach. Just that a spin out of a left, powered turn to final approach is more likely if pilots fail to use their flight controls properly.
Objection your Honour! No doubt you’re thinking that flying a right-hand traffic pattern from the left seat makes the runway harder to see on the downwind leg and when turning final approach. Well, I’ll bet that you’ve never complained about not being able to see the runway when flying right traffic from the left seat. Why? Because you’ll fly a slightly wider pattern to provide a view of the runway that pleases you. Problem solved! Flight controls can do many things to please a pilot.
In my opinion, the proper solution to prevent loss of control accidents (stalls and spins) in the traffic pattern is better training. Changing the behaviour of the pilot community, however, is a very difficult task. But, if flying left traffic makes stall/spin accidents more likely, then it makes sense to eliminate or reduce that condition if at all possible. The inventor, architect and futurist Richard Buckminster Fuller once suggested that he didn't try to change the way people behave. Instead, he found it to be more effective to change the environment in which people operate. Ultimately this results in people changing on their own. Perhaps we might substantially reduce pattern stall/spin accidents by changing the environment in which pilots fly, simply by changing the direction that pilots manoeuvre about the runway when landing”.