Early in my search-and-rescue career, I found myself in a river valley as a copilot. We’d been called out for three stranded teenagers on the wrong side of a river, with rapids separating them from safety. It was a confined area in the Smith River Valley of Northern California.
Although a ropes team was set up, it was determined that our helicopter was the best option for the rescue using our hoist. After much deliberation, we decided to short-haul the survivors from one side of the river to the other. The main downside was that we’d have to conduct the hoist from around 100 feet (30 meters).
We set up in the valley and lowered our rescue swimmer to the survivors. Once they were ready, we began our first hoist. With the first survivor safely off the ground, we started our transition left across the river. Halfway through that transition, however, the sun popped out from behind a grove of trees and completely bloomed out the pilot’s side of the cockpit.
After a quick exchange of controls, I stopped the aircraft’s lateral movement to regain our bearings. Unfortunately, that action triggered a large pendulum below us. Not having briefed for this potential outcome — and lacking experience with this type of emergency at the time — we had the hoist operator reel in the cable and bring both the swimmer and the survivor into the cabin.
Anyone with experience dealing with pendulums knows that was not the ideal solution, and, as expected, it only caused a larger pendulum to develop. All of this unfolded in a confined area with two people on the hook. Somehow, with time and patience, the hoist operator was able to work the cable and bring both safely into the cabin. We then chose an alternate location to drop off the survivors and managed to recover the remaining two teenagers just before sunset.
There were two major lessons we took away from that rescue. First, dry runs are free. I flew the MH-65 Dolphin in the Coast Guard, and we often joked that we were at bingo every time we took off. In a fuel- and time-limited aircraft, it was easy to feel the pressure to rush a hoist. Looking back, we had both the time and the fuel to conduct a dry run across the river. Our MH-60 brethren in the Coast Guard do this routinely, performing a dry run before every hoist using a checklist they call RIPR (rotor wash, insertion point, power, and references). Take the time to ensure your bases are covered and that you’ve thought through every possible factor by running through the evolution before doing it live.
Second, it’s imperative to consider the potential effects of spins, pendulums, and oscillations — and how to counter them if they occur during your evolution. These emergencies tend to arise at the least convenient time and can seriously endanger both those on the hook and the aircraft itself. Let’s look at a few ways to combat each of these challenges individually.
When pendulums develop, the resulting swing beneath the aircraft can be dramatic and difficult to manage. Fortunately, there are a few simple ways to reduce that motion by controlling the aircraft itself. First, a small “up” command will exert a downward force on the hook, helping to stabilize the load and stop the swing. Similarly, a gentle forward or lateral movement will apply a side force that can also steady the load.
This, of course, requires sufficient room to maneuver and no lead line attached at the time — though a lead line can also help prevent a pendulum from developing in the first place. Be cautious with lateral movements, however, as stopping abruptly can actually amplify the swing. Either raise the device while moving laterally or ensure you stop smoothly to avoid reigniting a large pendulum.
In my experience, even a small pull of the collective — even when tight on power — was often enough to kill most pendulums. You can test this principle yourself by dangling a pen from a piece of string in your office. A quick upward movement will show how the physics work as advertised.
Had we had the presence of mind that day to call for an “up 10” or simply give the collective a slight pull, we could have quickly stabilized the swing and continued the traverse with the rescue swimmer and survivor.
Spins are a different animal. They’re caused by rotor wash interacting with the device on the hoist hook. A spin tends to intensify as the device moves through the turbulent flight zone (TFZ), which extends roughly from half to one rotor disc below the aircraft. In this zone, the rotor wash funnels tightly and exerts maximum force on the device, often causing the spin to worsen.
The best way to stop a spin is to get the device out of the TFZ. This is where lateral flight becomes your best friend. Gaining effective translational lift (ETL) moves the rotor wash behind the aircraft, taking the device out of that turbulent zone.
Lowering the device below the TFZ can also help slow the spin and allow you to reset. However, be cautious not to raise the device higher into the rotor wash, as that will only intensify the problem.
Using a lead line can often prevent spins from developing in the first place — if it’s positioned correctly on the device. The Coast Guard has even experimented with using carabiners and breakaway lines instead of attaching the lead line directly to the spinning hook. If a lead line is in use and a spin does develop, be mindful that any lateral movement could cause entanglement, endangering both the evolution and the aircraft.
Oscillations — large, circular swings of the device on the hook — are caused by a combination of aircraft motion and rotor wash. This blend of spins and pendulums can be countered in much the same way: by moving the device out of the TFZ and flying the aircraft laterally through ETL. This introduces a new stabilizing force on the device while also moving it out of the rotor wash, stopping the oscillation.
During one training evolution involving through-canopy hoisting in a small clearing, we had a rescue swimmer whose hood came untucked and unraveled. The loose hood caught the rotor wash and sent the swimmer into a large oscillation beneath the helicopter. It was a powerful reminder to always be mindful of your gear and how it might affect your ascent into the aircraft. In that case, the crew was able to use lateral flight to stop the oscillation, as lowering the swimmer back through the narrow canopy wasn’t an option.
As I gained more experience in the aircraft, I began to practice and teach these emergencies in a controlled environment to better understand the aircraft and how to respond effectively. It doesn’t take much experience to avoid the potentially disastrous consequences of being unprepared for these scenarios — just the willingness to practice, anticipate, and learn.
