When the bell sounds


Dino Marcellino learns how helicopters are used in the Italian Alps to manage the threat of avalanches

The Alps span 745 miles (1,200km) of Italy’s territory and anyone in the area in winter must face a natural element that is both welcomed and poses a problem: snow.

As recent events have shown, major snowfalls in Alpine territory can be dangerous. Public safety is a priority for everyone in the Alps and especially for those managing public infrastructure, not least the managers of ski slopes.

Every year thousands of people go to the numerous ski areas and the many hundreds of square kilometres of snow-covered slopes in the region, and ski-slope managers therefore have great responsibility in ensuring the usability and safety of the slopes, especially when there is danger of a possible avalanche.

How to manage the danger?

The dangerous places where snow accumulates and could produce an avalanche are well-known and are usually always the same, so it is possible to put in place different forms of either passive or dynamic prevention. The best-known passive systems are the traditional avalanche barriers: nets, cruciform modules and rigid wooden or steel fencing that retain the snowpack at altitude and do not require specific management beyond routine maintenance.

Dynamic systems trigger an avalanche, which enables authorities to control the overall avalanche risk. Explosives are of course an effective dynamic system, but they require adequate safe storage, careful movement and trained technicians, so many managers of ski areas and institutions prefer to use exploders to create a controlled avalanche, and helicopters are indispensable for transporting these devices onto the slopes.

Gazex and O’BellX systems

The author spent four days in two different ski areas in northern Italy to see how helicopters are used to transport these systems. In one area, Cervinia-Matterhorn, two types of exploder were put in place: a fixed remote avalanche control system called Gazex and a removable type called O’BellX.

The Gazex device is mounted on a concrete base and uses a gaseous mixture of propane and oxygen inside open metal tubes connected to a gas storage plant, also placed at altitude by helicopter. When detonated, the Gazex device causes a shock wave of 3m3 (105ft3) volume, which creates an avalanche. The explosions are remotely controlled and take place above the snowpack; the system has complete autonomy for the entire winter season, enabling authorities to keep a large mountain face free of snow.

The removable O’BellX device explodes a mixture of hydrogen and oxygen inside an open cone and is also remotely controlled. This system can be installed and removed from the slopes by a helicopter long-line without ground assistance.

Flying in the mountains brings with it the challenge of difficult conditions, as shown by this photo of Pellissier Helicopters AS350B3 Ecureuil I-PHAX (msn 7828) operating in the Sestriere- Sauze d’Oulx dropping off a DaisyBell system.
All photos Dino Marcellino

Both the Gazex and O’BellX systems are available 24 hours a day in any weather conditions throughout the winter, with no limit to the number of shots; both can be installed in very inaccessible sites and ensure effective avalanche control, which reduces the likelihood of destructive avalanches.

For both devices, a concrete sole plate is built on the almost-vertical faces surrounding skislopes. Pipeline connections are built from the device to a gas unit. All material and workers must be transported by helicopter to the slopes, a job that requires experienced and specialised helicopter and ground teams.

Ecureuil in the mountains

An Airgreen Ecureuil AS350B3 was used on the first day of the author’s visit to Cervinia- Matterhorn, the crew consisting of pilot Alessandro Remine and technicians Edoardo Barberis and Lorenzo Olivo.

The day’s programme included flights up to the slopes taking materials and people to construct the Gazex and O’BellX systems, followed by other flights transporting roller conveyors for ski lift cables and positioning snow fan systems. Late in the afternoon the last rotations were flights to recover the workers at altitude.

Described like this, the work sounds simple, but it is in fact a very complex and demanding activity; at the end of the day the pilot has accumulated more than six hours of flight time and innumerable rotations.

The author experienced the rapid tempo of operations when, early in the morning, he was dropped off with the technicians on a ledge at an altitude of 11,318ft, practically with one foot in Switzerland and the other in Italy. From there the technicians went along a ridge and descended the slope to reach the installation point for the Gazex and O’BellX systems.

In just a few minutes of flight the helicopter had completed an impressive climb from the base camp in Cervinia village at 6,561ft in altitude. The author felt the height change, feeling uncomfortable because of the very low temperature and low oxygen and clumsy with the cameras, but the technicians were at ease and moved freely on the rocks.

In the meantime, Remine performed numerous rotations transporting components for installing the two systems. Each time a different load was deposited at the steep point of the slope.

A helicopter at work using a barycentric hook carrying loads of all sorts is fascinating to watch, even more so when that work takes place in the alpine environment with famous mountains such as the Matterhorn and Monte Rosa in the background.

Flying helicopters in the mountains is demanding on a pilot both from a physical point of view and piloting the machine to take account of the constant changes in temperature, pressure, oxygen and wind conditions. Flights must be adapted to the weather and terrain of the area.

An Ecureuil airlifts equipment and material to prepare the installation of the Gazex avalanche exploder system, pictured to the left.
Close co-operation is required between pilots and ground teams working on the mountains.

Flying in the mountains

Alessandro Pellissier, an AS350B3 Ecureuil pilot in the Sestriere-Sauze d’Oulx area, spoke about the challenges of flying helicopters in the mountains and triggering avalanches.

He told AIR International: “Here at the Sestriere and Sauze area we work at the maximum altitudes of around 9,842ft. In Valle d’Aosta, sometimes we reach 13,123ft. With 650kg of DaisyBell and the people on board weight management is critical. We divide the job into steps, little fuel on board, and at the same time try not to fly useless rotations so we don’t aggravate the costs to the customer.

“Some pilots work with the mirror, others with the bubble window. Everything can look white and grey. There are no landmarks, you cannot see if there are little elevations or depressions. Then clouds and sleet worsen the situation. It can be difficult to have the perception of distance from the slope, if you are too much tall or short. The DaisyBell’s laser system helps a lot, giving indication to the pilot on a dedicated display.

“After a snowfall often the wind rises, it is an element of nature with which you have to compete every day here in the mountains. Sometimes it is strong. Sometimes we are just below the ridge downwind; a wind that does not help you, indeed it crushes you. Other times we have only one possible approach, with the tailwind and crosswind.”

In addition, helicopter operators must also be responsive to the needs of the client and the job itself. A helicopter is an expensive machine and is paid for per flight minute, so it is necessary to maximise its potential to save time and money and satisfy the client.


Another helicopter in operation at Cervinia- Matterhorn was Kaman K-MAX HB-ZGK (c/n A94-0026) managed by the Swiss company Rotex Helicopter AG.

The K-MAX was developed specifically for air-work and optimised for external cargo load operations and is characterised by its intermeshing rotor and lone pilot. Despite its relatively small size, it is powerful and can lift 6,000lb (2,700kg), more than its empty weight. It is incredibly quiet, generates little downwash and is highly manoeuvrable. It is, however, expensive to operate, so it requires a perfect logistical organisation around it.

The K-MAX is used to transport the main one-piece metal module that forms the Gazex system’s exploders, which weighs 2,000kg (4,400lb). The Ecureuil, with its external load limit of 800kg (1,763lb), is used to transport the system’s smaller components plus accessories and workers.

The metal tube must be lifted by K-MAX at the correct angle for it to be coupled to the base and ensure the four concrete sole plate bolts are exactly connected to the four holes in the tube’s connection plate. The inclination tolerance is only two degrees, so everything is simulated on the ground using a crane before doing it for real. There is a detailed safety briefing for everyone involved: the crews of two helicopters and workers on the ground.

To put the materials in place the K-MAX hovers above the rocky ridge, using a 60m-long (196ft) line. The pilot stays in constant radio contact with the ground workers on the mountain below.

The main one-piece metal module of the Gazex system exploder weighs 4,400lb (2,000kg), hence the requirement for it to be airlifted to where it is needed.
A Gazex tube is airlifted into position by a K-MAX, the tube hanging on a 60m-long-line cable. The tube must be lifted at the correct angle to enable it to be coupled with the base, and the level of tolerance is only two degrees.

Thanks to the helicopter’s stability and the precision of its controls, coupling the Gazex and the concrete base was completed in a very short time. Immediately afterwards, the Ecureuil flew some rotations transporting the supports to secure the stability of the heavy tube.

The Ecureuil’s maximum weight of 750kg (1,653lb) makes it the right machine for the placement of the O’BellX system. A fixed foot bracket is anchored to a concrete sole plate. The bracket has stainless steel guide rails enabling the semi-permanent module to be positioned at the correct inclination.

The O’BellX system is fitted to its bracket just before the winter season by a single helicopter rotation and removed at the end of the season.

The pilot manages the module with the longline and must place it on the bracket’s guides, then check the stability and finally release the load. The pilot is alone in doing this work; no people are required on the ground. When the module needs to be removed the pilot must fly over it and, using the long-line, hook it and transport it down in the valley.

Triggering an avalanche

A third dynamic system for managing avalanches is in operation at an Italian ski-area on the border with France, and to find out more the author visited a helicopter base in the Sestriere-Sauze d’Oulx area on a very cold and windy mid-afternoon in February.

Above the village of Sauze d’Oulx, the base has a wooden chalet offering shelter and hospitality that serves as a meeting place for guests using the heli-skiing service. A large tent houses an AS350B3 Ecureuil and the necessary equipment for various types of work, as well as a mountain rescue service.

After the slopes close and skiers return home or to the hotel, the temperature drops quickly. It is time to go flying – which sounds strange, but in the next two hours the helicopter will be engaged in work that can only be done in the late afternoon or early morning when the lifts and slopes are deserted: triggering an avalanche.

Rotex Helicopter AG Kaman K-MAX HB-ZGK (c/n A94-0026) undergoing pre-flight checks in the Cervinia-Matterhorn area before lifting its cargo.
The K-MAX can lift 6,000lb (2,700kg), more than its empty weight, and is quiet, manoeuvrable and generates little downwash.
An AS350B3 Ecureuil with a DaisyBell. The avalanche caused by the detonation from the device can be seen on the slopes below.
An AS350B3 Ecureuil in the hover with a 60m-long line lifting the bracket and semi-permanent module for the O’BellX system at altitude.
The size of the DaisyBell system is apparent when pictured next to the AS350B3 Ecureuil that will carry it.

This is preventive work, undertaken to avoid dangerous accumulations of snow. It is carried out when snow cover exceeds 500mm (1.6ft) in depth by using an explosive gas system called the DaisyBell, transported by helicopter to areas where snow accumulation means a planned avalanche is required.

The DaisyBell, made from steel, is slung under the helicopter by a 60m-long cable. Two gas cylinders are installed on the external side of the device, one containing oxygen and one hydrogen. Two controls are installed in the helicopter cabin: one in front of the pilot and the other in the hands of the operator sitting in the left-hand seat. The entire system (bell, cylinders, mixers, accessories) weighs about 650kg (1,433lb).

With the helicopter hovering and the DaisyBell held at a height of between 5-10m (16-33ft) above a selected point, the mixers inside the bell are activated. Within five seconds they inject and mix the correct dose of the respective gases. The resulting ignition and explosion create a shockwave that travels at a speed of 2,200m/s (6,561ft/s), producing a very controlled blast which moves snow safely down a slope. When the DaisyBell is detonated, it does not generate shock or vibration on the helicopter.

Pilot Alessandro Pellissier explained the DaisyBell is capable of undertaking 40 consecutive shots, albeit with the limitation that after eight or nine shots the machine overheats, meaning they need to wait a moment to cool it, which is facilitated by the helicopter’s movement and winter temperatures.

Equipment and material for Gazex installation, including a gas storage tank, is air-lifted to altitude by an AS350B3 Ecureuil.
Airgreen Ecureuil AS350B3 I-AIRK (msn 3276) working at altitude with the Matterhorn in the background.z

With two controls fitted in the cabin operators can choose to select to inject only oxygen, which cleans the bell. A laser system detects the distance between the bell and the snowpack below, very important information for the pilot.

This controlled avalanche triggering is just one of the many tasks in the Alps for which helicopters are indispensable. This work continues year-round, in both winter and summer, year on year. A lot of people are engaged daily in this very exacting work, which requires expertise, technique, cleverness, adaptability and physical endurance. AI

In action

AIR International witnessed first-hand how the DaisyBell system clears snow.

Before flight the Ecureuil was ready on the landing pad, the technicians having installed the cylinders on the DaisyBell, verified the system and hooked the bell to the helicopter with a cable.

The manager of the skiing courses gives indications of where the avalanche triggering is needed. The first landing point is located on the Colle Basset, 7,942ft in altitude. After dropping off the DaisyBell the helicopter takes off to make a reconnaissance flight over the slopes and ridges to locate where snow had accumulated.

There was around 300mm (1ft) of fresh snow, low clouds and a light chilly breeze together with wind and a snowstorm generated by the rotor flux. In seconds the author’s glasses and camera are fogged and frozen, as well as fingers, despite the gloves.

The Ecureuil returns quickly and goes into the hover, hooking the DaisyBell and then flying away quickly. There is no time to lose. The helicopter climbs and approaches a slope at an altitude of about 9,200ft. Then it slows to the hover before the DaisyBell is detonated. A few seconds later, as the helicopter starts to fly away, beneath it a snow cloud grows, becoming ever-larger as it descends into the valley. The snow sweeps over the ski slopes; snowcats will be used to restore the tracks for skiers to enjoy the slopes safely the next day.

The operation is repeated several times in different places. With the poor visibility and an annoying drizzle persisting in the air, there was a clear realisation this is very hard work.