Estimated reading time 14 minutes, 58 seconds.
Photos by Anthony Pecchi
In a valley in the heart of the French Pyrenees mountain range, an Airtelis caravan and its technical assistance trucks settle on a flat stretch of land surrounded by rocky peaks. It’s the ideal spot to set up base camp for the renovation of a few miles of high voltage power line. On a site like this, an Airtelis Airbus H225 Super Puma, working alongside an RTE crew, can accumulate up to six flight hours every day.
The RTE Group is a subsidiary of EDF, the French national electricity production company, and is tasked with the management and maintenance of the country’s electrical transmission network. Airtelis is a further subsidiary of the RTE group, created in 2011 to offer its rotary-wing experience for external international customers, as well as to lease aircraft. For line maintenance, RTE uses its own fleet of light helicopters, mainly Airbus H125s and H135s, which are grouped together in the RTE helicopter works department (Services des Travaux Héliportés, or STH).
Heavier aircraft, such as the Airbus H215 and H225, have been brought together within Airtelis.
Airtelis’s H225s are distinguished at first glance by their blue and white livery, but above all by the attributes of the aerial worker with which they are equipped. Underneath the fuselage is a solid hook, allowing the aircraft to carry 10,470 pounds (4.75 tonnes) with a sling, while the cockpit is distinguished by bubble doors with large mirrors underneath the nose.
At the rear of the fuselage is a window installation used during cable unrolling activities. Through this window, an observer, lying on their stomach, has an amazing view of what’s going on underneath and behind the helicopter.
The two H225s, used by Airtelis for the last eight years, have each recorded just over 2,000 flight hours, mainly slinging or laying and removing cables.
“It’s a job that requires patience and precision,” said Frédéric Grandmougin, one of five RTE pilots qualified on the aircraft. Grandmougin is a former French Army and special forces helicopter pilot. Beside him is Jean-Claude Partiot, a former French Air Force helicopter pilot. The two men have a combined 22,000 hours of flight experience, and an intimate knowledge of the Super Puma aircraft family and aerial work.
In laying cables, the most spectacular work is done with an unwinder, which carries the reel and is hooked under a sling.
“The unwinder is slung 16 to 21 meters [50 to 70 feet] under the helicopter,” said Grandmougin. “It lightens as we progress, and we must be very careful with this gradual loss of mass so as not to see the load exceed an angle of 30 degrees from the vertical resultant, corrected for the attitude of the helicopter. The danger, by going beyond this angle, would be to no longer be able to release the device in an emergency, because the sling would remain blocked at the bottom of the hook.”
The control of this angle is ensured by the device, certified by Airbus Helicopters at the request of Airtelis. It consists of sensors, located on the hook, which send a signal reflecting the position of the sling. The hook angle is displayed on the aircraft’s multifunction display.
“When the specified limit is exceeded, a visual and audible indication warns us,” said Grandmougin. “Between 20 degrees and 25 degrees, we enter the ‘amber zone.’ Five degrees more, and we go into the red — immediate danger. [So] it is imperative to slow down and/or release tension on the unwinder.”
To minimize the risk of reaching this 30-degree angle, it is possible to generously ballast the unwinder with eight 90-pound (43-kilogram) weights. The aircraft also has cameras mounted under its fuselage: one pointed downwards to film the unwinder, the other oriented at 45 degrees to film the hook. The images are then displayed on a multifunction display in the cockpit.
Most line surveillance work in France is completed with RTE’s H125s. However, in urban areas, the twin-engine H135 is required for the enhanced safety of redundancy.
All lines, from 63,000V to 400,000V, are regularly inspected. The work is done systematically with a crew of three.
Richard Muriasco has been an RTE pilot for about 15 years, having begun his career in the Bell 47 as an agricultural application pilot. He then worked at Hélicoptères de France, SAF and then with Heli Inter in Guyana.
“The line survey is done by going up the cables at a speed of about 30 knots,” he told Vertical. “The pilot sits on the right, with a navigation aid operator on his left, closer to the powerline, who monitors vegetation, line crossings, obstacles and animals. Behind us, an operator registers all the faults that we find.
“A good inspection requires putting the cable ‘in the sky’ to see it well, and therefore flying lower than the electrical structure,” Muriasco continued. “If it is relatively easy to do with the … 400,000V [cable being high off the ground], you have to be extra careful with the 63,000V [cables] which are much closer to the ground and obstacles.”
In winter, when the lines are well charged electrically and the ambient temperature is low, the inspection is done with an infrared camera: a damaged line heats up abnormally, creating hot spots that are easily visible in thermography.
“The entire network must be inspected for thermography at least once every three years, always with the same crew of three,” said Muriasco. Each pilot performs between 500 and 700 hours of line inspection flights every year.
Heli-Basket work on live lines is another essential activity for RTE, and perhaps even its core business. The Heli-Baskets are specially-designed cages suspended underneath the aircraft at the end of long cables, within which line technicians are carried. RTE has been using them for over 30 years for cable repair operations or to replace equipment.
These operations are flown with the H135 T3, which began to replace the Airbus AS355 N in RTE’s fleet in 2018. The last RTE twin-engine Twin Star still in service was due to be retired by the time this story is published. Occasionally, Airtelis H225s or AS332s can also be leased to fly Heli-Baskets.
Twin engines are essential for safety. With two engines, two pilots, two fitters, two radios for communication and double slinging, RTE doubles up wherever possible for greater safety.
“The performance requirement is greater for Heli-Basket work because we must be able to do better than hover and extract ourselves from cables on an engine,” explained Pierre-Yves Denis, a pilot with 20 years’ experience in aerial work. “The regulations require [us] to be able to display a rate of climb of 150 feet per minute on one engine to free oneself from cables, which always remain under tension.”
The Heli-Baskets weigh around 220 pounds (100 kilograms), and accompanied by two fully-equipped operators on board, they represent a load of about 770 to 880 lb. (350 to 400 kg). To ensure the required performance on one engine, the variable of adjustment is therefore fuel. The helicopters usually take off with very little range when the weather is hot, but a refueling truck is never far away.
As of February 2021, RTE’s H135s fly without a door, to provide the best possible downward visibility, but the company has ordered bubble doors for the type. A set of options, developed by Airbus Helicopters in the U.K., includes a double hook under the helicopter to improve safety in the event of an accidental release, as well as an anti-rotating system installed between the skids to prevents the Heli-Basket turning on itself.
“The helicopter-borne Heli-Baskets are never hooked to the cable on which we are working,” said Denis. “The technicians are seated or standing, depending on the Heli-Basket, and face a kind of balcony installed in front of them, which is used to lift the cable from below.”
“An advantage of the H135 is its rigid rotor, which makes it possible to have a very stable helicopter — which is very popular with technicians!”
It is the traction applied with the helicopter that stabilizes the Heli-Basket and the cable, Denis explained.
“Potentiometers show us precisely how much force is taken on by the cables, and a camera on each side of the cockpit allows the Heli-Basket to be properly centered,” he said. “The images are displayed on a screen, where information on the cable tension is also displayed. An advantage of the H135 is its rigid rotor, which makes it possible to have a very stable helicopter — which is very popular with technicians!”
Work with the Heli-Basket is done in teams of nine people, including two pilots in the helicopter: one for the actual piloting, the second for checking the parameters, the electrical environment and providing all the information necessary for the work. Four technicians, who work four or five weeks a year with Heli-Baskets, take turns working inside them in teams of two. A refueller, a mechanic and a site manager complete the team. With the Super Puma, the Heli-Baskets can accommodate four technicians in a deployable version. The work, however, is carried out with the power off on the powerline.
Marketing the know-how
Beyond its work in France, one of Airtelis’s missions is to market RTE’s know-how to other network operators in Europe. The company also leases its helicopters for work completely outside the electrical maintenance sector. For example, one of Airtelis’s H225s has spent several years working at the Cazaux Air Force base to help train H225M crews from the French Air Force.
Its work can also include emergency response operations. These could be classic firefighting missions with a Bambi Bucket (Airtelis began working with the French Sécurité Civile in 2016, and an aircraft was stationed in Corsica throughout the summer of 2020), or lesser-known missions relating to the nuclear rapid action force (FARN). FARN was established after the Fukushima disaster in Japan: it aims to provide the capability to rapidly move heavy equipment (electric generators, in particular) to a nuclear power plant that has experienced an incident.
A fourth axis of development for Airtelis is working as a consultant and providing training missions for other operators. Airtelis crews trained Chinese pilots in lifting operations, for example, and as of February 2021, negotiations were ongoing to train Hydro-Quebec technicians and other Canadian operators in Heli-Basket work on live lines.
For its capacity to offer a tailored service to suit its clients’ needs, and high-quality work performed with a mind always on the safest mode of operation, Airtelis now has an enviable reputation for excellence that extends well beyond the borders of its native France.