AS350 B3e course · Flying the Astar
Mountain and high-altitude flying
Wind, power margin and a way out
The essentials
Mountain flying is about three things: wind, power margin and an escape route.
Wind over terrain produces updrafts on the windward side and sink and turbulence on the lee. Density altitude reduces power exactly where you need it. And confined sites and pinnacles leave few ways out.
The Astar is very capable up high — which is why it gets taken to places where all three problems come together.
Reading the wind
Wind flowing over a ridge rises on the windward side and descends, often turbulently, on the lee. Approaches are made into wind on the windward side wherever possible, where you have lift and smoother air.
Clues: cloud, snow plumes, dust, trees, water, and how the aircraft behaves on a pass over the site.
Source 1
Up, down and round
Between the rising air on the windward face and the sinking air beyond the crest there is a dividing line, and it moves with the wind. On the windward side of it you have lift; past it, sink that can exceed what the aircraft can climb against.
On the lee, the air can roll over into turbulent eddies below the crest. Through passes and saddles the wind is squeezed and speeds up. And the stronger the wind, the stronger all of it.
Finding the wind on site
Clues on the ground tell you the general wind. The wind at the site you get from the aircraft: fly a circuit around it at a constant height and speed, and watch the groundspeed, the drift and the power needed on each leg.
Where you need more power to hold height, you're in sink. Where the aircraft is bumped, there's turbulence. The leg into wind with the least power is usually the approach.
Source 1
Reconnaissance
Look at a new site before committing: a high pass for the wind, the approach, the departure and an escape route, then a low pass for surface, slope and obstacles — especially wires.
Decide in advance the point at which you'll abandon the approach, and the direction you'll go when you do.
Source 1
Planning the approach
Into wind, on the windward side, and along the slope rather than straight at it where you can, so that turning away is always a turn downhill into clear air.
Pick a go-around point: past it you're committed to landing, before it you can still leave. Fly to the landing point itself, not to a hover high above it — a hover out of ground effect is the most power you can ask for.
Power on site
At altitude, the margin between power available and power required shrinks. Before committing to a pinnacle or a confined landing, check what power the hover will need compared with what you have — the charts and a power check on the way in.
Arriving with a margin is not the same as leaving with one: the departure may be downwind, or over an edge with no ground effect.
Checking power on the way in
Before the approach, know two numbers: the power the site will take — from the hover chart at the site's pressure altitude, temperature and your mass — and the power you have, where the FLI will reach its limit.
Then check it in the air near the site, at a safe height, before you're committed. If the aircraft needs more than the chart said, the chart was wrong about today. Up high the first limit may be temperature or gas-generator speed rather than torque — the FLI shows which.
Density altitude on the day
The chart is entered with the conditions at the site, not at the base you left. Sites are higher, and in the afternoon often warmer, than the morning's planning assumed.
Fuel burned gives you capacity back; cargo picked up takes it away. The worst moment of the flight is usually the heaviest departure from the highest, hottest site — plan for that one.
Source 2
Pinnacles and ridges
On a pinnacle there is no ground effect until you are over the pad, and nothing under you beforehand. As you slow you lose translational lift just as the ground falls away — the approach that needs the most power ends where it is least available.
Leaving, the escape is the edge itself: accelerate off and over it, trading height for airspeed, rather than trying to climb out of a hover.
Confined areas
Trees and walls make the wind swirl and can hide it entirely. The reconnaissance asks: is it big enough for the rotor and the tail, what's the surface, where are the wires, and which way out has the lowest obstacles into wind?
Getting in and out vertically means hovering out of ground effect. If the power isn't there for that, the site isn't there for you today. Watch the tail rotor in any turn in a clearing.
On which side of a ridge do you expect the smoothest air and lift?
Windward. The lee side has the sink and the turbulence.
What's the purpose of the high reconnaissance pass?
The high pass is for the big picture. The low pass is for the surface, slope and obstacles.
Departing a pinnacle with limited power, what's the priority?
Airspeed. Translational lift reduces the power needed; a climbing hover asks for the most.
Which conditions do you enter the hover chart with for a mountain landing?
The site's. It is usually higher and may be warmer than where you planned.
Sources
- Helicopter Flying Handbook (FAA-H-8083-21B) · FAA · Chapter 10, Advanced Flight Maneuvers
- Helicopter Flying Handbook (FAA-H-8083-21B) · FAA · Chapter 7, Helicopter Performance
- Aviation Investigation Report A04A0050 (AS350 B3) · Transportation Safety Board of Canada
- Helicopter Flying Handbook (FAA-H-8083-21B) · FAA · Chapter 11, Helicopter Emergencies and Hazards
Educational only. Not approved training material, and never a substitute for the Rotorcraft Flight Manual, an instructor, or your operator's procedures. Figures marked as manufacturer data or test results are not limitations. This content is a draft and has not yet been reviewed by an instructor.