Mountain Flying for Helicopter Pilots: Essential Guidelines

Spotting the dangers and flying safely

The UK’s CAA has published (November 2024) a great Safety Sense leaflet on how to fly in the mountains, although it is aimed at light aviation generally. Helipaddy Premium customers can download the Helipaddy Helicopter Mountain Flying Guide for free at Mountain Flying which provides a deep dive for helicopter pilots.

Here is the CAA CAP3048 leaflet: https://helipaddy.com/wp-content/uploads/2024/11/cap3048-safety-sense-35-mountain-flying.pdf

The leaflet, while primarily aimed at powered fixed-wing aircraft, does include sections relevant to helicopter pilots or aspects of mountain flying that could impact them. Here are key points that specifically affect helicopter pilots or their operational considerations:

Wire Hazards:

Hidden Wires: Power lines and other wire obstructions pose significant risks, especially for helicopters, which may operate closer to terrain and at lower altitudes than fixed-wing aircraft. The leaflet advises identifying wire routes, looking for pylons on charts, and maintaining a safe separation from the valley floor and mountain sides to avoid these obstacles. Crossing wires safely often involves flying directly over supporting pylons, where visibility of the wires is clearer.

Terrain Clearance and Valley Flying:

Low-Level Flight Hazards: Helicopter pilots frequently operate in confined areas, which may limit options for escape. The leaflet suggests maintaining an escape route while navigating through valleys and advises flying along the right side to maximize visibility and reaction time. Limited maneuvering space in valleys can be particularly challenging for helicopters, requiring a safe altitude margin.

Reverse Course: For helicopters, the ability to reverse direction in valleys is crucial. The leaflet advises positioning the aircraft high and close to one side of the valley wall to optimise turning space, a maneuver helicopters may execute more flexibly than fixed-wing planes but still requires caution.

Aircraft Performance at High Altitudes:

Reduced Performance: High-altitude conditions reduce hover and climb performance for helicopters due to decreased air density. Helicopter pilots must be aware of how pressure and density altitude affect lift, which is critical for maintaining control in “hot and high” mountainous conditions.

Climb Gradient and Power Management: The leaflet addresses climb gradients, recommending Vx (maximum angle of climb) or Vy (best rate of climb) as appropriate. For helicopters, maintaining a balance between altitude and forward airspeed is essential to avoid settling with power in high-altitude operations.

Meteorology:

Mountain Waves, Downdrafts, and Rotors: These atmospheric conditions can lead to severe turbulence and rapid altitude changes, potentially overwhelming a helicopter’s climb capability, especially in strong downdrafts. The leaflet warns of downdrafts up to 3,000 ft/min, advising helicopters to maintain sufficient altitude and reduce airspeed to stay within safe limits when encountering these phenomena.

Lenticular Clouds and Fog: Fog forming in valleys and lenticular clouds at altitude require careful monitoring. Helicopters are particularly affected by sudden fog formation at lower altitudes, impacting visibility. The leaflet advises checking for weather variability over short distances and being prepared for abrupt IMC and to use GAFOR when available.

Navigation and Moving Maps:

Reliability of GNSS: The leaflet notes that GNSS signals may be unreliable in mountainous terrain, particularly in deep valleys where signal degradation can occur. For helicopters, often flying close to terrain, maintaining visual terrain reference is crucial, and they should use GNSS as a supplementary rather than primary navigation aid.

Human Factors and Hypoxia:

Hypoxia: Operating at higher altitudes for prolonged periods can lead to hypoxia. Helicopter pilots, who may not routinely fly at such heights, should use supplemental oxygen above 10,000 ft, monitor oxygen levels, and recognize hypoxia symptoms, as helicopter flights may also involve significant time at these altitudes in mountainous regions.

Emergency Planning:

Contingency Plans for Diversions and Landings: Due to their flexibility, helicopters are better equipped for emergency landings in varied terrain. However, the leaflet advises helicopter pilots to identify safe landing areas along routes, maintain sufficient fuel for diversions, and consider the extended flight time that may result from challenging terrain or weather.

These points emphasise the need for helicopter pilots to consider wires and other low-level obstacles, performance changes at altitude, meteorological risks unique to mountainous terrain, and careful navigation and planning to ensure safe mountain operations.