Fliegen im Gebirge

Flying in summer and mountains – what you need to bear in mind!

Editorial team

13.08.2025

Last week, Fliegermagazin published an article on a final report by the SUST. The sad outcome: a flight over the Alps ended fatally for the three occupants. Last weekend, two paragliders also died in accidents in the Swiss mountains. The article goes on to say: “Flying in the mountains is challenging. Accidents happen time and time again because pilots overestimate the capabilities of their aircraft. Even locals and experienced pilots are not immune to this.”

Flying tactics in the mountains – better too high

A flight in the mountains must be well prepared. Forget about flying in a straight line over the Alps and through the mountains. Conditions in the mountains are completely different from those in the Swiss Plateau. The airspace is smaller, the wind and weather conditions are more challenging, and air traffic with gliders, motorized aircraft, helicopters, and paragliders is more varied and intense, especially on weekends. This means that pilots need to be fully focused. A detailed briefing is therefore essential to ensure that you have the necessary capacity to fly safely. The points to be observed have already been covered in the article Briefing, flight tactics and crossing passes. In brief, these are:

Never fly into a valley unless you are at least 1000 feet (or 2000 feet in windy conditions) above the pass behind you at the entrance to the valley.
Also, do not fly in the middle of the valley, but on one side or the other so that you always have enough space for a possible turn around. As a rule, this will be the right side of the valley, unless there are downdrafts there; be careful here, as you may encounter oncoming traffic on your side of the valley! See & avoid is therefore very important when flying on the left side of the valley!
Always cross the pass at a 45-degree angle from the side so that you can easily turn back into the open valley if you can’t continue behind it. Keep an eye on the variometer and altimeter as you approach the pass. If your altitude suddenly drops, it’s the right time to turn back and try again.

Source: Runwaymap.com

Density altitude, climb performance, and control behavior

Some like it hot…aircraft do not! Hot air temperatures mean lower air density. In short, this means less lift and less performance. All pilots learn during their training that serious flight preparation includes calculating the takeoff distance. This is especially true in summer: in addition to a significant increase in the takeoff distance, the climb rate also decreases massively. Poor climb performance must be anticipated in flight planning, especially when flying over aviation obstacles or mountain ranges. Once in flight, it is (usually) too late.

Hot temperatures not only have a significant impact on engine performance during takeoff or cruise flight, but also on the flight and control characteristics of an aircraft during landing. Warm air is thinner, so the wing generates less lift at the same speed. To achieve the same lift, the aircraft must be flown at a higher approach speed. Control response can be sluggish, especially in slow flight shortly before touchdown. Pilots often have to apply greater rudder deflections to achieve the same control effect.

Source: UBC ATSC 113 – Density altitude, Determine “density altitude” and explain why pilots use it

Warm air turbulence during landing – the invisible danger

Flights can be turbulent, especially in summer. Most of the time, we just get shaken around a bit. Why is that? On sunny days, the ground heats up unevenly, with dark surfaces (asphalt, fields, rocks) warming the air more. When the warm air gains enough lift, it separates from the ground as a thermal bubble and rises. This rise can occur very suddenly.

Thermals: rising warm air – the natural lift in the troposphere – MeteoSchweiz

When approaching the short final – an already critical phase of flight – detaching warm air bubbles can pose a real danger, especially at low altitudes. This is because speed and energy are low during this phase and, depending on the situation, there is little time to compensate for the flight attitude.

How can this danger be minimized? If sweat is running down your back in the cockpit due to the hot summer temperatures, it is advisable to postpone your flight until the morning or evening. This is because the thermals are weaker at these times of day. If you don’t want to miss out on the experience, you should increase your approach speed slightly in turbulent conditions (safety margin) and be prepared for sudden wind changes or warm air bubbles. In addition, in strong thermal conditions, choose a runway with a clear approach and few heat surfaces on final approach, if possible.

Source: Michael F.H. Krutina, Schematic representation of the separation and ascent of a heated air parcel.

“The mountains are higher in winter”

Editorial team

16.01.2024

Snow-covered mountains have a fascinating and attractive effect. On a day like today, there is nothing more beautiful for pilots than a flight over the white Alpine landscape. But we should not be dazzled by all this white beauty. Flying over high mountains and especially over ridges has its pitfalls and involves a number of risks, both in winter and in summer.

“The mountains are higher in winter”. That’s an old aviation saying. What does that mean? Cold air is denser than warm air. In relation to the pressure surfaces, their height therefore changes with the temperature. However, the altimeter in the airplane is not able to react to the temperature, which is why there are differences between the displayed altitude and the actual altitude. So remember: the difference is four percent of the altitude for every 10° deviation from the standard temperature, i.e. minus for cold air and plus for warm air.

The following points also apply when flying in the mountains:

Mountain crossings should not be carried out above a closed cloud cover. The high altitudes required and the associated sharp drop in engine power could lead to unexpected flight conditions under instrument meteorological conditions (IMC) between invisible mountain peaks.
Vertical air currents are much stronger in the mountains than in the lowlands. Passes should therefore be approached with a safety bank of at least 1000 ft AGL (300 m) and from the side in such a way that a return turn can be made without danger if the terrain behind the pass is obscured by clouds.
A pass should not be crossed in a climb, but horizontally or in a descent with sufficient airspeed to be able to fly through downwind zones quickly.
Pilots with little experience in mountain flying are advised to refrain from crossing the Alps or to abort the crossing in good time:
a) in foehn conditions;
b) in the event of a weather report: “Alps in the clouds”;
c) if thunderstorms are observed;
d) in case of shower activity (also in summer);
e) if the cloud base is too low over the passes.
Last but not least: For Alpine crossings, it is recommended to file an ATC flight plan and to carry a portable ELT (emergency transmitter) (SAR 1, SAR 2).

The Swiss Powered Aircraft Association illustrates this important aspect in an article from “Safer Flying” from 2015, which is still relevant today. The video “Flying in the mountains” also provides you with further valuable information on what you need to bear in mind when flying in the Alps.

#aviation #avsafety #winterweather #flightplanning #flightoperations #aviationgeek #weareGA #pilots #flying #generalaviation #airoperation #SafetyCulture