Rotex Helicopter AG was founded in Balzers, Liechtenstein, in 1997 with the objective of offering a professional service targeted specifically at medium-to-heavy load-lifting. During the company’s first ten years a single Kaman K-Max was its only machine and during that first decade it accumulated more than 14,000 flight hours, firmly establishing the reliability of the helicopter and the efficiency of the Rotex team. Rotex added a second K-Max in January 2007, and continuing growth in demand for the K-Max resulted in the addition of a third example in 2017. Rotex Helicopter has now amassed more than 45,000 flight hours on the type and has established itself as the European leader for helicopter transport of loads up to 6,000lbs. Although the company is based in Balzers, the helicopters are only ever ferried to the main base there for major maintenance – 100-hourly checks and above – due to the complex operation necessary to operate this unique type.


The single-seat K-Max was developed and manufactured in the USA by Kaman Aerospace Corp, exclusively for the load transport role. Weighing in at 5,070lb empty and with a 6,000lb payload, it is one of the few helicopters to boast a payload greater than its own weight. The synchronized (Flettner system) main rotors boast a lower-than-typical noise level (72DB) and generate reduced downdraft, which is both much more comfortable and safer for ground crews, especially during forestry work. The two geared rotors are mounted on a V-shaped shaft, with each set of blades rotating in opposite directions so their torques cancel each other out, increasing lift and eliminating the need for an anti-torque device. The type’s lack of a tail rotor results in reduced loss of performance at higher density altitude conditions, making the K-Max an exceptionally suitable platform for lifting at altitude and/or in high temperatures. Drift plays a role in yaw movement but what really changes direction is the angle of attack of one of the blades which varies according to the desired direction. Pitch is corrected by a horizontal stabilizer that is controlled by the collective position and controls the pitch attitude to stabilize the machine with the speed changes. This replaces the fixed stabilizer found on other types.

Power is supplied by a 1,825hp (1,341kW) Honeywell T53-17-A-1 turbine, limited to 1,520hp at takeoff and 1,370hp in flight to increase reliability and service life. Cruising speed is 100kts and the service ceiling is 15,000ft. The rotors on the 4.14m-tall aircraft each have a diameter of 14.70m and the machine’s overall length is 15.85m. It burns 320 liters of aviation kerosene each flight hour from its 831-liter internal fuel tank and its two-and-a-half-hour endurance gives it a maximum range of 480km.


Rotex K-Max operations span all of Europe, although the bulk of the work is conducted in Switzerland, Austria, Germany, Italy, and France. The steady expansion and evolution of the company’s operations over the years has resulted in a complex, efficiently choreographed logistical support system that continuously serves the three K-Maxes as they travel around the continent. Different contracts in Europe are sorted and studied to organize the most efficient route to get to the different sites without returning to the base. The machines and support teams follow one another from site to site and a complete work schedule is maintained for about three months ahead. While almost any another helicopter type can transport the teams and materials necessary for its mission itself, this is not possible with the single-seat K-Max due to its lack of internal capacity. This adds a huge organizational constraint because the helicopter never goes to a worksite without its ground crew. Landing areas must be a minimum of 25 meters square, and whether it is an aerodrome or an out-landing area, the established advance schedule facilitates mechanical service to meet the aircraft onsite to carry out minor checks and common maintenance. Valentin Molk, project manager at Rotex, elaborated on the need for the large support infrastructure, explaining, "For example, if the weather is unstable or if a customer wants the K-max to intervene but has not organized it in advance, we cannot go to the site as quickly and easily as a more conventional helicopter. Because the K-max does not return to base in the evening, our standard operating configuration includes a tanker truck, mini-buses for the crews and the equipment truck, not to mention the management of hotels to accommodate our crews. The logistics are enormous, and our teams travel about 100,000 km each year to follow the helicopter wherever it goes.” In order to meet these logistical needs, Rotex owns four JCB Fastrac forestry tractors, three tanker trucks ranging in capacity from 10,000 to 23,000 liters, three equipment vehicles and five staff vans. This range of vehicles allows each K-Max to constantly have a standard configuration of equipment at its disposal.

Flying the K-Max

Qualifying on the K-Max requires training flights in a different aircraft type, as there is no dual-seat training option for the K1200. Kaman Aerospace operates a K-Max pilot training center in Connecticut, USA, where ground and simulator training are followed by approximately four hours of flight training in the Huskie H43; the only other helicopter type equipped with the same type of rotor system as the K-Max.

Around seven hours of solo flying in the K-Max follow the Huskie training to complete a pilot’s K-Max validation. ‘Beat’ is one of Rotex’s K1200 pilots, flying the K-Max about 75% of the time and spending the remaining 25% flying the AS350 Squirrel for another company. His total of 3,700 flying hours now includes 600hrs on the K-Max.

He explained that he started slowly, getting to grips with the K-max by doing some simple load carrying and not exceeding two flight hours per day because of the fatigue. “The K-Max has no hydraulic aid for the controls, so the piloting is very tiring compared to a B3. You need a good grip on the cyclic and the effect of the pedals is very limited due to the absence of a tail rotor. If you force the controls it doesn't work, you can't force the K-max to do something it doesn't want to. It can become a real drag when it's windy, you can do a 180 before you can stabilize your machine and lift your load,” he described. "Beginning in the K-Max can be very hard, crossing the Alps alone at 11,500ft in the wind is particularly stressful and challenging, because you can't fly the K-Max with two fingers. Everything vibrates a lot and it's a totally different way of piloting than the rest. You have to adapt to the K-Max and not to constrain it, understand how it works, how it reacts. Once this is understood, however, it is a magnificent machine,” he summed up.

Logging Operations

In Switzerland, supporting and slinging logged trees is a daily mission for the K-Max. The activity accounts for about 70% of their work. This activity is one of Beat’s favorite missions with the K-Max as he says it is the most successful in terms of organization with the operators on the ground. It consists of clearing forests inaccessible to forestry tractors or removing trees that threaten infrastructure in locations where conventional felling is not possible. "The view of the loads is great,” he enthused, when explaining his opinion of the K-Max and his preference for tree-cutting work. “We have an armrest that we place under our shoulder to reach the collective and relieve the rest of the body when lifting. The available power is great too, of course, but what I like most is that K-max work is real teamwork. We spend the week together, the evenings at the hotel, and we live very beautiful moments when the operation goes well. Forestry is a complex operation to organize and is very intense. All the positions are very important so when it goes perfectly, it's great." For tree cutting, a dozen operators on the ground are composed of loggers, climbers and ground operators, divided into three teams. The climber must hang a sling in the tree and evaluate the weight. He then decides whether to cut the tree in several sections or to cut it entirely, trying to average two tonnes per lift to give the pilot room to maneuver, with the pilot announcing the weight of each load on the radio after every lift to give the ground crews a more accurate indication.

Tree cutting is usually done before winter as the trees are drier, reducing their weight, and because the leaves on the trees are falling which enhances pilot visibility. Once the tree is ready, an operator hooks the sling to the K-Max’s hook, and the pilot puts it under tension for the cut. This is the most delicate part of the operation, as too much tension makes it very dangerous for the logger who risks being hit by the tree. An operator is therefore responsible for always having a visual on the tree to warn his colleagues if danger is imminent. Insufficient tension, on the other hand, can cause the saw to get stuck under the tree or the tree to fall on the logger. At the time of the cut the state of the tree is still unknown, it could be internally rotten and dislocate at the time of lifting, or could also be weakened and split along its length. To limit the risk of splitting, the Rotex teams cut the tree in two stages. The usual sling is approximately 75 to 80m long and with about 20 to 40m of that length fixed to the trees. The electric hook brings the average total length to around 80 to 100m with 55m the actual distance below the helicopter.

The seven missions that Rotex typically flies include logging, special skidding, a hydraulic wood grapple, load transports, assembly/disassembly of installations, firefighting and humanitarian aid. The company now employs eight pilots, five project managers, and thirty flight assistants, loggers and climbers. The aircraft can lift around 550 tons per day and during its 25 years of operations, Rotex’s K-Maxes have lifted some 1,550,000 tons of material and completed about 800,000 rotations, during approximately 28,000 interventions for about 2,700 clients. These numbers show that Rotex’s far-sighted decision to build a company and operation focusing on a very specific niche market segment has proved highly successful, with a high probability of long-term stability and continued growth.