Conduct a safety drill, have your passenger yell out SWAY!!

I don't see the point of making rules about doing it only when stopped. Why bother at all?

You'll be subconsciously prepared to reach for the lever at every stop, because you know that these are the conditions under which someone is liable to initiate one of your "sway drills."

The load on the driver is greatly diminished at a stop as well. In a real sway situation, you'll be busy trying to keep control of the tow vehicle, mindful of any nearby obstacles and/or traffic. There's a lot more to do while moving.

Plus as grit dog stated earlier, sway events aren't sudden, unless you are not paying any attention at all.

I also agree that applying the trailer brakes when the trailer broke loose around that corner would have been detrimental.

Well I tried it, at a stop light with nobody in the car. I just kept my eyes on the intersection and made a stab for where I thought the brake controller was.

1st attempt...I smacked the lower dash, pulled my hand back and reached lower and...smacked the lower dash again. Took my eyes off the intersection to look and I was still about 4 inches too high. At least now I know to reach very low if I want to reach it.

In seriousness, following my sway thread, lol.
The point is, the more mentally prepared you can be for "probable" situations, the better you'll fair most of the time.

Like driving in inclement half winter weather.
I'm a regular user of the brake check when roads are wet, possibly icy. Or snow packed but maybe better, maybe worse traction.
Even easier when towing the sled trailer. Can just stab the trailer brakes and watch how it reacts in the rearview.

No need to grab the binders and drive 20mph when the first sno flake hits the window, but if you don't see spray off of other's tires, time to figure out how slickery it is before you find out the wrong way.

I see what you're saying Wild Bill 888. Though I don't think I hijacked the thread. But I did give too much information which allowed it to drift in a way I didn't expect. The thread is supposed to be about getting to the brake controller fast enough to stop a sway event. And not about what I should have done in the trailer losing traction event from the story.

The too much information is where I even related the story about the trailer sliding sideways on the corner. The event happened so fast that by the time I even thought about the brake controller the event was over. Whether the controller would be the correct action in this event is not really relevant.

The relevant part is that I didn't even think about the controller until the event was over. I've seen enough youtube videos and read enough posts on here about trailer sway that I know that sometimes it happens slow and builds, and sometimes it happens in an instant from the bow wave of a tractor trailer blowing by at 80 mph.

I found some of the replies to this post interesting. People talking about always being on the alert, or always scanning for danger, their trailer is set up correctly etc. When in fact stuff happens. We are all human and we all make mistakes. We take our eyes off the road to look at the speedometer, to look at the clock, to look in the rear view mirror at the face the kid in the back seat and scold him for bothering his sister. Maybe there was a death in the family and we're deep in thought driving 10 hours to circle the wagons. NOBODY, and I mean NOBODY looks at the road and scans their mirrors 100 percent of the time that they are behind the wheel.

So this is where this post comes in. Picture yourself deep in thought cruising down the road about 55 mph on a clear wind free day. You've been on the road for 3 hours and on the same straight stretch of road for about 45 minutes. You are lulled into a false sense of security as you're watching the road ahead for debris. Nothing is happening up ahead so you briefly turn your head to your wife to ask where she wants to stop for lunch. At that moment a tractor trailer that you hadn't noticed blows past you doing about 85 mph and the bow wave puts your trailer in a violent sway event. Or it's a windy day and you come out from a tunnel or from under an overpass and a huge gust of wind hits your setup from the side and starts a say event.

Is now the time that you want to think about where exactly is that brake controller lever? I guarantee you will not even want to take one hand off the wheel, let alone take your eyes off the road to look for that brake controller. Yes I'm talking about that brake controller that you haven't even put a finger on in the last 5 years because it is already setup the way you like it. My point is that when the event happens you may not have time to think, you may only have a second or two to react before the situation is unrecoverable. And that is why you should practice, or drill, or pretend, or whatever you want to call it, to get to that lever.

The idea of having someone yell sway was to startle you out of your sense of security and shock you into action like that burst of wind had just occurred. The idea of only doing this when stopped is so you don't accidentally flinch or slam on the brakes or something and wind up in an accident. If you don't want them to yell sway that's fine. Ask you wife to gently put her hand on your arm and say "Honey, the trailer is swaying"

It doesn't matter what the trigger is. What matters is how fast can you make a controlled grab at the brake controller lever. If you do not practice at least a few times; You're probably going to lose precious seconds in trying to pry your hands off the wheel and get to the lever.

It is a bit ironic that opnspaces hijacked his own post by including the word sway (dynamic instability) in his post. A careful reading of the opening post reveals that he is describing loss of traction on a curve.

Trailer tires are generally made of hard rubber for long life, and they tend to have a lower coefficient of friction than good car/pickup tires. That can be a good thing as you might prefer to have the trailer skid sideways a bit rather than roll over, but on old worn wet pavement traction may be a lot less than you think. The hard trailer tires will be the first to break loose, which is a lot better than the rear axle of the tow vehicle.

Reread all the comments with this in mind and you might come to a different conclusion.

Wild Bill 888 wrote:
Because it's a proven way to get the trailer back under control.

Great, link to the carefully controlled engineering tests that prove

Here you go Wild Bill, these people know way more than YOU and I about stopping a trailer sway event.

https://www.dexteraxle.com.au/what-is-dexter-sway-control/

We are all different as is our setups...

My rituals when towing...

Manually check and adjust the trailer brakes (no longer own, but borrow from buddies and church members) and my TV’s. Check and readjust the trailer brakes along the trip. Even rebuild their trailer brakes if it is worn to much. They like it when their trailer is returned in better shape, brake wise. If I cannot skid the brakes, pass on that trailer

Always check the trailer brakes before leaving by manually skidding and by using only the TV’s brake pedal (won’t skid, but know that works)

All along the trip, touch the TV brake pedal and feel the trailer brakes engage, which keeps them in their temp range.

Yes, I’m anal when it comes to braking...more important to me than go power. #1 is braking; #2 is handling (that includes staying within specifications); #3 go power, performance; everything else on my have to have

If your trailer is sliding and braking will send it over...then you are lost regardless what you do...

Clicky
Nothing else needs to be said

Because it's a proven way to get the trailer back under control.

Great, link to the carefully controlled engineering tests that prove the maximum possible cornering speed is with trailer brakes on. What engineering principle determines the optimum braking force? Sometimes it is helpful to consider extreme examples to understand what happens between those limits.

Case 1: Trailer tires are rotating freely with no braking at all. All of the force generated by the skidding tires is applied parallel to the axles pushing the trailer back into position with the maximum available force.

Case 2: Brakes locked, tires skidding like a hockey puck. the force generated by the tires is parallel to the skid marks. The Component of force parallel to the axle is small at small angles, increasing to 100% at 90 degrees of trailer rotation.

My guess is some people in this situation recovered despite applying the brakes and credited the recovery to their lightning fast reflexes.

There is another condition I’ll call Dynamic instability, where the trailer can start swinging side to side. This can happen on a straight dry road with maximum traction. Braking the trailer tires helps this condition by REDUCING the lateral force and speed.

I don't think you want to manually apply the trailer brakes in this situation of the trailer sliding sideways. Just off the throttle is best, possibly light braking.

I have actually never applied the trailer brakes manually.

The very last thing I need is a passenger yelling anything.