Time To React
Managing Terrain Clearance

 

If something goes wrong when flying close to terrain, there is not enough time to react to critical situations (collapses, surges, spirals, spins, etc.). Perhaps a reserve deployment could be a solution. With, but with low clearance, the ground might come into play before the reserve has time to open.

The source of flying events can have a correlation to terrain proximity. Rotors, thermal release points and terrain features can be the source of the event. From low altitudes, tricky events can happen swiftly, and it is easy to see that we could reduce incidents and accidents by better managing terrain clearance. In the worst case scenarios, if you need to toss your reserve, having some extra altitude could be the difference between a successful deployment and a terrible crash. Increased clearance from terrain will reduce the events, as well as provide time to react.

There are many factors involved in our decisions of how close we fly to the terrain. There is no one figure that applies to any site or pilot for how close this can be. If you are flying mid-day at a strong thermal site in relatively stronger winds and on a higher rated C or D class wing, you would be wise to use a much higher clearance. On such a tricky day, scratching might be removed from your flight to pad your safety. There are times when scratching is a good thing, but we need to include a wide range of relative factors to reduce terrain clearance. If we make terrain clearance one of our top priorities, I am sure this will help eliminate many accidents.

Factors that should be involved in decisions for how much clearance to maintain:

  • Weather
  • Time of Day

  • Type of Flying Site (Smooth Ridge Soaring vs Thermal Flying)

  • Crowded or Uncrowded Air

  • Wind Speed

  • Terrain Features

  • Pilot’s Skill Level

  • Class of Glider being flown

RIDGE SOARING – On a day with steady winds, experienced pilots will fly very close to the terrain at a coastal ridge soaring site. With smooth winds, the pilots can “scratch” close to the ridge or cliff-side, as long as they ensure not to get downwind of any mechanical turbulence trigger. Even a newer pilot with ridge soaring experience can fly relatively close to the terrain in such conditions.

In strong or cross winds, clearance needs to be increased. In strong winds, the mechanical turbulence will increase and carry further from triggers. When triggers are lower on a cliff or ridge, the rotor will carry further and have more pop than in lighter winds.
When the wind is cross, you have to adjust your picture of where the rotors will carry. In this scenario, it is wise to add some height or stay further upwind of the areas that the rotor may be directed. While ridge soaring, if you are near the rotor, you are also low enough that a reserve toss will not have enough height to work if you encounter a bad piece of rotor.

In addition, you will need the clearance, which will need adjustment between the upwind and downwind passes. On the upwind passes, ground speed will be lower, and this will make steering adjustments easier and allow for flying closer. On the downwind passes, ground speed will be much higher. With higher ground speed, the terrain comes at you much quicker, and you need more clearance from the terrain and steer with your eyes looking further ahead. You can use a “3 second rule” to make this point. When flying on the upwind pass, 3 seconds ahead will not be very far down the ridge, as your ground speed will be lower. On the downwind pass, the ground speed is much higher, so 3 seconds ahead will be much further.

Coastal ridge soaring sites have the wind blowing in smoothly over the water, and there is normally very little thermal influence to the air. As long as you fly upwind of the terrain features, you will have fewer problems with mechanical turbulence. Inland ridge soaring sites are not always the same in this regard. Your guard needs to consider subtle differences like this. In strong winds, a small terrain feature has greater potential to change how the air flows up the slope. Make sure to change your tolerance when conditions change.

MOUNTAINS AND THERMAL SOARING – In mountain conditions with thermals and more dynamic terrain (ridges, spines, canyons, trees, etc.), tolerances need to increase. Because of this, critical situations can happen more often and with more severity. With this in mind, more clearance is necessary.

In more active situations, where flying in thermals and or mountain terrain, increase both vertical and horizontal clearances to help you have an “out” should you encounter turbulence or sink. In general, the minimum would be 300 – 600 feet or more, both above and upwind of the ridge. Altitude above terrain is usually more of an estimate for most of us. So, this is more of a ballpark figure. In lighter conditions, flying closer than this will sometimes be necessary, but the point is to pad this as much as possible, and by doing so, you will have time to react when anything unexpected occurs.

Scratching is “flying closer to terrain and working hard to stay up or climb slowly”. The distance you pad yourself from the hill should be adjusted to the conditions. When flying mellow thermals in the later afternoon, you can work closer to a ridge, but you still need enough room should something unexpected come along. If you are going to scratch, figure 8 turns can be used instead of 360s. Figure 8s allow you to stay closer to the hill, because you avoid the downwind portion of the turn necessary in a 360. The severity of a collapse or wing event when on the downwind portion of the 360 has far more critical potential than having the same event while flying parallel to the hill or turning away from the hill while doing figure 8 passes. When your skills grow to XC type flying, scratching can often be necessary, but scratching should only be done in locations where there is a bailout if you do not have success.

A fairly common issue occurs when pilots that mainly fly coastal soaring sites visit thermal sites. These pilots tend to fly closer to terrain and have more comfort scratching in the mountains than they should. This is a mistake, thermals and mountain conditions have more variables and potential for turbulence in more places.

When your clearance is great enough to use 360s, make sure and plan clearance for the inside part of the turn when you will be closest to the hill. If the lift dissipates, or you exit the thermal or have a collapse, you need time to correct the wing. You also need to regain directional control. You could call this your- “just in case, space”.

There is no magical number that works for every pilot or level of glider. The point is to consider all the factors, so that you have the time to deal with wing events when they occur. Instead of being desperate to catch that nice thermal above the higher mountain spine, go and look for lift above lower spines or points. This will give you a lot more terrain clearance and make you less vulnerable.

One of the things that makes paragliding so tricky to package safety with is the huge number of variables that pilots need to manage. The factors that you manage as a pilot are diverse and dependent on skill levels, types of wings, weather and unexpected variables. One absolute that we can help our safety with is to keep enough time to react and deal with any event. Scratching skills are a great thing to have as a pilot. Scratching needs temper and adjustments for the variables present and changing on each flight. If you are going to scratch, you need to measure the risks carefully. As the saying goes, plan for the worst and hope for the best. The ending point here is that when flying near terrain, “plan for the worst”. If an event happens, you can then deal with the event and the “hope for the best” part.