Mountain Flying Awareness

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Mountain flying can open a fun and exciting world for a pilot! Gorgeous views, exposure to industry operations like heli skiing, confidence crossing ranges, or access to coveted airports are all attractive prospects. However, there are some important considerations in mountain flying, and it can be extremely hazardous if the pilot is unaware of the extra risks or fails to respect them.

The focus of this article is on high altitude and mountain flying awareness; tips for getting  through the terrain. Approach techniques to landing sites, landing site considerations, or maneuvering within mountain terrain are beyond our immediate scope and purpose.

We will divide mountain flying awareness into five categories: helicopter performance, environmental, physiological, navigation, and backcountry preparation.

Helicopter Performance

When planning a flight that will include mountain terrain, the performance capabilities of the machine is paramount! Although you may not be expecting an off-airport landing in a high altitude or mountain environment, it’s appropriate to understand your performance limitations in the event you need to make a precautionary landing to handle a warning light or other emergency. Even if you feel confident that you will be able to conduct an approach to an in-ground effect hover, planning for a power margin beyond what the IGE hover charts predict—up to and including OGE performance—is a more realistic power management plan. Uneven terrain, unpredictable winds, turbulence, and visual degradation like snow whiteout can all contribute to unexpected needs in hover performance.

Consider a temperature/altitude envelope or performance table in your performance planning to allow for changing conditions through the flight or unusual situations like an inversion layer. Typically, this is a table that includes changes in mass as fuel is burned, temperature, and altitude, so the pilot can make more appropriate power management decisions based on the most current information. This table requires careful preflight planning since the pilot will need to calculate fuel burn rate and predict changes in weight and balance, in addition to forecasted temperatures at different altitudes.

Once you’ve determined your power needs, be sure that your helicopter is up to the task! It’s easy to assume that bigger is better, and flying a larger twin engine helicopter translates to having “power for days.” In fact, most operators in high altitude and mountainous terrain choose smaller, single engine helicopters like the H125 or MD500 due to the gross weight to power ratio.

Environmental

Awareness of wind direction and speed is critical when flying in the mountains. Preflight planning and weather predictions are excellent for the prevailing winds in the area; however, the local, small picture wind conditions can change minute to minute. A pilot should consistently evaluate both prevailing (macro) and local (micro) winds by understanding how the air interacts with the surrounding terrain.

At the most basic level, the wind rises as it slopes upward with terrain; this is called the “windward” side. As the ground falls away, the wind also falls and comprises the “leeward” side. Knowing where these regions are is critical to mountain travel. Windward slopes on mountains have little turbulence and provide for favorable updrafts, which allow the helicopter to have positive power and lift. Flying on the leeward slope of a mountain is much more hazardous due to the increased turbulence, potential for rapid changes in speed and direction, and strong down drafts that could cause the helicopter to impact terrain. In general, the more rugged the terrain, the more turbulent the wind.

Be aware that air passing through tight valleys or saddles will increase rapidly in speed due to the Venturi effect. When crossing a ridge or saddle, fly at an angle between 20 and 45 degrees to the ridge. If cloud ceilings, wind conditions, and performance allow, maintain several hundred feet of altitude above the ridge to allow for options in maneuverability.

The mountains are extremely dynamic! Weather conditions, precipitation, and winds can change at any moment. Operations in mountain valleys can lead to entrapment, even if no clouds or fog are predicted. Before they roll in over your preferred escape route, locate several avenues for egress. Don’t assume that the weather in one valley is the same as what you may find over the next ridge. Research the terrain in your flight planning and strategize multiple routes to get you to where you need to be.

Physiological

A few physiological issues can arise while flying at the higher altitudes typically necessary to clear mountains. In addition, being surrounded by high peaks and deep valleys removes the presence of a horizon, which can disorient the pilot and crew and make it difficult to ascertain true distances, resulting in proximity miscalculations regardless of altitude. The addition of any other challenges like turbulence, visibility, or precipitation can further increase the risk of spatial disorientation.

Several studies show severe impairment due to hypoxia beginning as low as 9000’MSL. High altitude and increased exposure time have cumulative negative effects on cognition, decision making, memory, and motor skills. Hypoxia also has dangerous effects on eyesight, including the loss of depth perception, peripheral vision, and a reduced ability to focus. Since the body is compensating for the lack of oxygen, dehydration is also common at high altitude. If in a rescue/forced landing situation, or prolonged flight at higher altitudes, watch for symptoms such as decreased mental capacity, slow reaction times, circulatory problems, and vertigo. Often, physiological issues related to altitude can mask each other! For example, the symptoms of acute mountain sickness include headache, nausea, rapid heart rate, and reduced reaction times, all of which are also symptoms of dehydration.

Navigation

While flying over flat land, direct line of sight navigation or GPS navigation can be appropriate. Obstacles and rugged terrain, even small foothills, will pose threats along a route, and it is necessary for the pilot and crew to have a clear understanding of the visual references they may encounter to ensure a safe route from Point A to Point B when navigating in this way. By comparison, a direct line of sight route- aka “following the pink line”- would rarely be appropriate in the mountains. Flexibility and appropriate planning, complete with alternate routes for egress, is crucial. Consider the impacts that indirect navigation can have on fuel burn, weather conditions, terrain options, and limited communication reception- both radio and cell- when planning a route through the mountains. One way to create this flexibility in flight planning is to utilize enroute decision points (EDP) or enroute decision triggers (EDT) for critical places or components of the flight, such as a fuel source, expected deterioration in weather, questionable ceilings over a mountain pass, or estimated fuel burn to the next source. Developing your EDP/EDT’s in the preflight planning phase and being respectful of personal minimums along the route can help avoid the tendency to push on when facing poor weather, an aeromedical issue, or a limited fuel situation.

Backcountry Preparation

When risks of a flight operation increase, so should your preflight planning and emergency contingency options. This can include, but is not limited to, communication devices and tracking, survival equipment, supplemental oxygen, or equipment on your helicopter such as bear paws or auxiliary fuel tanks. Having survival gear on board and knowing how to use it is critical for operations in any remote environment, and especially mountains. Items to consider: satellite communication device, First Aid kit, emergency shelter, fire starter, signaling device, extra clothing, food, water, and/or a water purification and collection method. Emergency Locater Transmitters are not required for many helicopter operations, however, they are recommended.

Where do you store survival gear? Many survival situations may have been averted if some of the equipment- even warm layers or a basic first aid kit—was more accessible to the injured crew. If stored in a cowling or covered compartment, be sure all persons aboard are aware of their location. At the very least, having a few items on your person, such as a communication device (like an inReach or Spot) and access to warm layers, can make a big difference in an unanticipated or emergency landing.

Conclusion

Mountain flying, whether high altitude or not, can be very fatiguing due to the mental and physical management of winds and terrain, precarious weather conditions, hypoxia or other physiological concerns, and the added apprehension of flying, where every moment poses a new set of choices. Before embarking on a mountain flying adventure, receive proper training on route planning, mountain flying techniques, navigation, and backcountry survival. Acknowledging your limitations and those of your machine, and taking actions that set you up for success, is a way to demonstrate the respect that the mountains deserve. Happy flying!


Jessica Meiris
Pathfinder Aviation

Professional mountain guide, Helicopter Pilot, Safety Advocate

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