The Czech company Primoco UAV SE has been successfully expanding its high added value applications for its UAV. One of the ways to use the aircraft is for flight calibrations and inspections of airport radio security, i.e. radio navigation systems such as VOR, ILS, DME or military TACAN, but also optical elements such as VASI, PAPI and other means used to ensure the precise approach of aircraft. These devices must undergo periodic calibration to verify that their characteristics comply with the required standards. Until now, the most common aircraft used for this activity were specially modified aircraft, often based on the Cessna Citation or Beechcraft King Air types. However, in recent years, the trend has been towards cheaper platforms and increased availability of calibration, so calibration service providers are trying to find new and more efficient ways to perform calibration. Unmanned aircraft, of course, represent one of the very promising avenues of development. The Czech unmanned aircraft One 150 not only offers excellent payload capacity, a footprint for special equipment and on-board power grid capacity, but is also built in accordance with the requirements of the latest European regulations based on EU Regulations 945/2019 and 947/2019.
Last year, Primoco UAV started cooperation with the world’s leading provider of calibration technology, Norwegian Special Mission (NSM). Although the collaboration was dramatically affected by travel restrictions preventing experts from both companies from physically meeting, the integration of the calibration equipment into the aircraft was conceptually completed last year and the first flight tests were conducted. The whole concept consists of a modular fitting (antennas, wiring, UNIFIS calibration unit and Trimble precision navigation unit) to the UAV, which is completely identical to the equipment carried by manned calibration aircraft, and can theoretically be shared between platforms. The main difference lies in the fact that in the case of a unmanned aircraft, the data is not evaluated by a specialist on board, but on the ground at the control station or anywhere else in the world (the unmanned aircraft is equipped with remote access technologies, so the specialist does not actually need to be at the calibration site at all). If the receiving system is identical to manned aircraft, the evaluation software and outputs are identical. Therefore, the customer is practically unable to know from which source the data confirming the parameters of his radio equipment originate. In addition, if a unmanned aircraft is used, the cost of flying the aircraft and the stay of part of the crew is eliminated, as the calibration specialist does not need to be on site.
The One 150 aircraft used for calibration was in a new configuration. To reduce the risk in case of an emergency, it was equipped with a ballistic rescue system from the Czech company Galaxy GRS. In this weight category, this unmanned aircraft is the only one with a similar system. It can be activated manually or automatically according to the set parameters, and it was tested over the Písek airport before its live deployment. During the Icelandic flights, experimentation with the reflecting surface of the calibration system antennas on the sides of the fuselage was expected. Therefore, the aircraft was fitted with a copper conductive foil. It was planned to place it in different places, but the first configuration has already shown sufficient signal reflectivity and will therefore become part of the general production (the foil will be inside the fuselage).
Standard Flight Activity
After a series of initial tests at the factory airport in Písek and VOR flights in the area agreed by both cooperating companies, it was necessary to perform the most challenging part of the tests – the calibration flights of the ILS system. Both companies were extremely interested in carrying them out in the Czech Republic, but the responsible entities did not have the will to support such a project other than verbally. The choice therefore fell on Iceland for several reasons. First of all, the conditions in the chosen period were definitely not ideal in terms of weather conditions, and the flight verification was therefore conducted in conditions corresponding to the actual deployment and it was possible to verify the accuracy of the aircraft even when compensating for wind gusts and not only in a calm environment. Furthermore, Icelandic air traffic control ISAVIA decided to perform a check calibration with the piloted aircraft and to make all the data available to the Norwegian company. These come from the same UNIFIS series device and thus the same reporting value of the compared data sets is clearly demonstrated. Last but not least, the Icelandic Aviation Authority Samgöngustofa was able to fully approve the SORA specific risk assessment according to the new European regulations for unmanned aircraft. The routes therefore ran directly in the required trajectories, regardless of the population density of the area below, as the authority recognised the high safety of the unmanned aircraft.
The OK-X053Z One 150 was brought to Iceland in a van from Denmark on a ferry. The Primoco UAV team was responsible for its layout and on-site preparation, while the calibration equipment on board was handled by a representative from NSM. A flight briefing was scheduled for the morning of 23 August 2021 with representatives of all stakeholders to discuss safety procedures. In the afternoon, after 2 pm, the Czech unmanned aircraft left the ground for the first time and started its flight activity. This consisted of ILS descent trajectory raids and overflights between calibration flights. During the calibration of the descent, the Czech aircraft was located up to 30 km from the airport and at altitudes over 3,000 ft. The maximum speed achieved on several flights was 100 kts (185 km/h), but many flights had strong headwinds of up to 25 kts. Despite this, all missions were flown in three days with a total flight time of 10 hours. And it should be added that the unmanned aircraft required no more than a visual and electronic check and refuelling at all times. The first flight shift was also marked by the verification of communication with the air traffic controller, when the pilot of the aircraft was constantly in radio contact with the tower. As they gradually gained experience, the controllers allowed themselves not to interrupt the unmanned aircraft’s flight activity in case of the arrival of other aircraft and, on the contrary, to guide them to landing even in the situation when the unmanned aircraft was moving around the airport with the transponder switched on. Again, using the same ADSB-Out transponder functionality as standard manned machines and the ability to operate safely in the common airspace was verified in practice.
The calibration parameters obtained by the One 150 UAV represent, according to the analyses to date, a solution fully corresponding to the accuracy of the piloted machines. More manufacturers of calibration systems are showing interest in unmanned aircraft as the future of the industry is clearly very much linked to UAVs. However, in contrast to multicopters with a limited payload capacity, the One 150 type offers the use of calibration equipment identical to the piloted types and therefore with the same data conclusiveness. That the future is unmanned is evidenced, for example, by statements by Australian, Spanish or Dutch air traffic control, which no longer envisage manned aircraft for calibration in the longer term. Today, the Czech-Norwegian solution represents the only unmanned aircraft in the world capable of offering both compliance with regulatory requirements for the aircraft itself and calibration results identical to manned aircraft.