When landing helicopters in potential obscuration conditions, there are two techniques that have worked well for me over the years. Whether the rotor wash kicks up loose earth causing a brownout or snow causing a whiteout, the techniques used to mitigate the obscuration are alike. While best to avoid these conditions by having ground personnel pack the snow, wet down a dusty area or find another landing zone, there are ways to manage the risk.
Unless you have a wheeled helicopter and a surface for a safe run-on landing, you likely need to land with zero groundspeed. This can be done safely using one of these techniques, without the risk of losing visual references and basically becoming IMC in a hover.
The Shallow Approach
The shallow approach is my preferred method in flatter terrain and a large area without obstructions.
Before discussing the actual approach, the “rotor wash contact point” should be understood. This is the point where the rotor wash meets the ground, and where the obscuration is formed. Its position, relative to the aircraft, is a function of aircraft airspeed, tilt of the rotor disc, and surface winds. All these variables affect where on the ground the obscuration will be formed and where it will drift after being formed. For example, decreasing airspeed or moving the cyclic aft will move the rotor wash contact point closer and more beneath the aircraft. The pilot can control the position of the obscuration cloud, by managing airspeed and the fore/aft position of the rotor disc.
As the approach is made, allow the aircraft to gradually slow down as you near the landing area. Looking to the side, you will see the obscuration cloud catching up from behind as you slow. Allow the natural drag of the aircraft to be the cause of slowing, not aft cyclic. Any use of aft cyclic will quickly move rotor wash contact point, and thus the obscuration cloud, forward.
With practice it is possible to make a shallow approach to your precise landing spot without aft cyclic, resulting in a touchdown with the obscuration just reaching the mast area. One caveat is that you need to be sure of your touchdown area; this is not the time for a slope landing or to be unsure if it is a suitable landing area. The procedure is to touch down just as the groundspeed reaches zero, without ever having the rotor disc tilt aft of horizontal.
The wind can be beneficial or detrimental, so be sure to make the approach into the wind, even if just a few knots. A headwind will help keep the obscuration aft as long as possible, and help slow down the helicopter to a zero groundspeed without aft cyclic. If the wind is strong you may even be able to hover, keeping the cloud aft. If you need to slow a little quicker during the approach, use a little pedal to get out of trim and increase the drag. If I’m solo I will use the same pedal as the side I’m sitting on, to better see the obscuration cloud behind. If I have another person on board, I will use opposite pedal so that I can better see the landing area, having them watch the cloud.
For training purposes, I have flown over a snowy field at 50 feet and practiced moving the snowy obscuration cloud fore and aft, using the cyclic, but always keeping it behind. With practice you can position it and keep it exactly where you want as you make your approach. Think of it as flying two objects, the helicopter and the cloud.
The Steep Approach
This is a good technique when the area does not allow for a shallow approach, when unsure of the actual landing area, or when there is a hardpan of dirt or snow just below the loose stuff. This technique does require more aircraft performance than the shallow approach technique, and an extended period of time hovering out of ground effect. Realistically, I do this technique about 80 percent of the time, and the shallow technique about 20 percent.
Make a slow and steep approach to your landing area, keeping the descent rate less than 300 feet per minute; settling with power considerations. Terminate to a hover, typically between 20 and 100 feet, at the first sign of an obscuration forming on the surface. The height this occurs is a good indicator of how bad the obscuration potential is. (I had a rule of thumb flying EMS at night: anything more than 75 feet was unacceptable and I would opt for another LZ.) Hold the hover as the obscuration dissipates. If there is a hardpan under the loose dirt or snow, it will get better. Adjust your altitude as necessary to remain above and clear of the obscuration. In a no-wind condition, it may take a couple of minutes for the obscuration to dissipate.
If the obscuration dissipates and you think it safe to land, find an object very close to your landing spot to use as a visual reference, preferably just a few feet in front of you at the 2 to 3 o’clock position (sitting right side). A rock, bush, twig will work; anything that won’t blow away. If the rotor wash unexpectedly kicks up more dirt or snow during landing, this may be your only reference to control the helicopter.
Should you ever find yourself in instrument conditions in a hover from a brownout or whiteout, you basically have two not very good options. If still high above the ground, pull max power and hopefully fly out of it without losing control, or if close to the ground lower collective and hopefully land without rolling the helicopter. Be safe and remember: it’s better to use superior judgment, avoiding the necessity of superior skill.
(These views and opinions are my own and do not necessarily reflect the views of Era.)