Precision helicopter guidance for cities and emergency support
Background & Objectives
A helicopter’s capability to operate to and from locations without landing aids, for example in medical evacuations or rescue missions, often makes them the only feasible method of transport. Compared to aircraft, weather conditions have a lower impact on helicopter operations and respective flight safety. For example, weather threats concerning wake vortex and windshear events are not as dangerous as they are for aircraft because the helicopter has better manoeuvrability at lower speed and will not stall because of airspeed. A weather radar is useful for avoiding thunderstorms but its warning or information are less critical than those for terrain or traffic. Airborne support to emergency medical services and search and rescue missions is often performed under bad weather conditions or at night, implying poor visibility and great danger. Due to the lack of performance of today’s onboard navigation system, a great number of missions have to be aborted causing loss of human life.
Currently, the Western European helicopter market for emergency and medical support (EMS) is served by 125 operators running around 450 helicopters. These have been supporting two distinct missions: transport from the scene of an accident to hospital and transportation between hospitals. Despite the fact that most of these helicopters are fitted with digital autopilots and are instrument-flight-rules certified, nearly all EMS operations are carried out under Visual Flight Rules (VFR), even in adverse weather conditions. This is due to the lack of helicopter-specific IFR procedures and the lack of a landing system suitable for helicopter instrument approaches.
HeliCity aims to fulfil a demand by developing and demonstrating a support system using EGNOS (and Galileo in the future) as the enabling technology for precise positioning with an adequate level of accuracy, integrity and improved positioning performance in terms of continuity.
HeliCity has identified a need for a secure, affordable positioning system that provides improved capabilities to helicopters and, more specifically, improved positioning system performances. Performance here is not only meant in terms of accuracy, but also of safety (integrity of the position) and continuity. GNSS, and in particular EGNOS and Galileo, are the candidates to answer this need. The concept proposed by the HeliCity project is to enhance flight safety by giving the crew the means to be aware of their surrounding environment and enable them to adopt a corrective action.
For helicopters, it is a means of enhancing operational possibilities for VFR flights especially under low visibility conditions during the approach and landing phases, even though always in VMC. This means that the HeliCity prototype will be a good way to help the pilot watch external threats and be aware of the surrounding geographical environment. IFR certification issues were largely beyond the scope of the HeliCity project. HeliCity evaluated the use of EGNOS on helicopters as part of an emerging solution to improve the ability of helicopters to fly in adverse meteorological conditions. To achieve the project objective, the team has integrated the HeliCity prototype – a GPS/SBAS receiver together with a cockpit display unit – on a helicopter.
The main goal of HeliCity was to develop and demonstrate a pre-operational system supporting enhanced positioning services aimed at helicopter VFR operations performed under adverse conditions and scenarios. The HeliCity system was based on the coupling of a high quality EGNOS receiver and a cockpit display unit which enabled the display of the helicopter position to the pilot. This system was evaluated in a sequence of flight trials which occurred in the Lisbon area in the summer of 2006. During these flight trials, both the performance and HMI improvements were evaluated.
Work performed & results
In order to assess both the analytical and operational aspects of the overall system, the HeliCity project set up an evaluation programme which relied on the performance of flight trials. The flight trials were conducted with the main purpose of evaluating the performance of EGNOS within a civil aviation context, expressed in terms of Required Navigation Performance parameters specified by ICAO. These parameters are accuracy, integrity, availability and continuity. The analytical evaluation was performed by comparing the helicopter positions obtained by the data logged by the onboard system with positions data resulting from using the CP-DGPS (Carrier Phase Differential GPS) method. Another important objective of these flight trials was to technically verify the system, proving its reliability and usability in real flight situations. To accomplish this objective, a simulated Helicopter emergency medical service mission was chosen to allow demonstrating the usefulness of the HeliCity system in missions where flights may occur in poor weather and low visibility conditions, always with the highest safety standards. The evaluation of the system’s operational aspects, such as usability and HMI improvements, was performed by interviewing the test pilot.