Eurocopter seeks OK for IFR approaches to hover

 - October 8, 2007, 7:02 AM

Eurocopter is making further strides toward its aim of certifying a helicopter to make IFR approaches to a hover, over a given point on the ground and at a defined height. By the end of this month, a second phase of flight tests involving a specially modified EC 155, currently under way near the OEM’s Marseille headquarters in southern France, will be complete. Then come the (arguably more challenging) tasks of writing up the reports and entering certification talks with the DGAC (France’s air regulatory authority), with a view to certification in 2007. However, the test results will come
as no surprise to DGAC: the regulator is actually partnering with Eurocopter and partially funding the program, as part of a European Commission environmental initiative known as Respect 2000.

The “hélicoptère tout-temps” (HTT or 24-hour helicopter) program was launched at the beginning of 2002. An EC 155 was equipped with a standard Eurocopter fully coupled autopilot, augmented by a new Sagem DGPS-driven card to enable it to perform steep (up to 10 degrees) approaches to a pre-determined hover height above a helipad at an airport or in a city center. Controlled by what is essentially an extra-powerful PC workstation, the system generates the three-dimensional information and symbology necessary both to prove the concept and to help the crew safely monitor the aircraft’s approach.

The third dimension is required because the pilot, carrying out a steep approach to an unfamiliar point on the ground, needs information about any obstacles (wires, masts and so on) in the area, as well as his or her position on the flight path. The bulk of the work on this part of the project was completed during the first flight-test phase in 2002. In part it included the integration of a Hellas laser radar, loaned by Eurocopter parent company EADS, from which raw data would be processed to an image projected onto a head-up display, thus allowing the pilot to keep watch outside the cockpit as the ground looms into view.

To be comfortable for passengers and crew, a 10-degree approach demands a low airspeed and relatively high rate of descent, so the autopilot algorithm needs to be carefully written to eliminate any risk of entering a vortex-ring state. These trials have been based on a speed of 30 knots–about the bottom limit for accurate pitot-static readings. Arresting that speed relatively quickly to zero places great demands on autopilot authority, to limits that only new-technology aircraft such as the fly-by-wire NH90, or fly-by-light EC 135 testbed, can currently provide.

This means it won’t be an entirely hands-off affair, according to project manager Daniel Bouheret. “For a conventional helicopter we expect the pilot to take control during the final 200 feet of the approach,” he said, “and modify the approach angle to perhaps 6.5 degrees before finally transitioning to the hover.”

At the start of the initial trials, the required degree of accuracy made it necessary to refine the signals using a ground station, meaning a differential GPS must be used. They were performed using an old, obsolescent Airbus DGPS ground installation. Later on, thanks to the loan of an EGNOS (European geostationary navigation overlay service) receiver from the European Space Agency (ESA), the team was able to replace the ground station. Since then, and throughout this second test series, it has used the EGNOS receiver exclusively.

Bouheret and his team can now deliver all the accuracy they need through the Inmarsat EGNOS system, whose satellite signals are corrected using ground stations positioned all around Europe (the European equivalent to WAAS). This system is now in place and in a test configuration–it is expected to be operational next year and to enter service in 2007, coinciding with a hoped-for certification of a production HTT.

Flight Tests Going Well

Bouheret takes up the story: “With the navigation system and DGPS installed, we made the first series of flight tests, as planned, between October 2002 and March 2003. We tested the flight management system functions, based on a three-dimensional route, and all automatic and manual control functions. It gave us good results all round, with the flight plan and approach path represented on the mission display and ground proximity color-coded relevant to the aircraft’s position.”

As well as DGAC input, every aspect of the trials was also assessed by a pilot from France’s CEV (Centre d’Essaie en Vol, or flight-test center) from nearby Istres. To the same extent as the Eurocopter pilots, he was in a position to suggest improvements. “During the second phase, with his help,” said Bouheret, “we also tested a new autopilot mode to allow the helicopter to make a fully automatic three-dimensional approach, all the way from cruising altitude to a hover at about 40 feet above the ground.”

Eurocopter also had a contract with ESA to install an EGNOS satellite receiver, which was demonstrated to agency officials at the La Fare airfield, near Marignane, on March 12 last year, the last day of the first flight phase.

After that, Eurocopter developed a new series of tests for the second flight-test phase, dedicated to the obstacle-warning system based on laser radar detection, with avoidance symbology developed by Eurocopter. “We also worked on the ground collision avoidance system that gives the pilot both audio and visual alerts,” noted Bouheret. “For the first phase we developed flight management functions and considered potential dangers all around the route using a 3-D database. For this phase we considered the actual space around the aircraft and its vector–like GPWS, but developed especially for the helicopter. Of course this is much more sensitive, and gives the pilot his final ‘pull up, pull up’ alert before hitting the ground.

“We also developed new symbology for the Thales HUD to provide the pilot with guidance information and specific obstacle warnings along the flight path. We were able to present HUD imaging through both infrared and an image intensification camera and can now display one or the other in the background to the HUD symbology, mainly during the landing phase. It is similar technology to some fixed-wing certified equipment but, as far as I know, this was the first time it was fitted to a helicopter. This was not fully demonstrated but tested in a ‘sphere’ fixed-base research and development simulator in Marignane, which is designed to help develop new control functions and enhance human-machine interfaces. When this was complete, we started flying again this past March.”

Further Testing for Night-flying Compatibility

Eurocopter successfully tested these navigation improvements and is currently engaged in a further assessment flight phase with a number of pilots. A night-flying program will test the night compatibility of the cockpit layout. Said Bouheret, “We have a DGAC contract to write the specification and define the equipment needed to provide all-weather capability in a production helicopter and to satisfy the DGAC, which has to done by the end of this year.”

To help pilots navigate, engineers have installed a “mouse” pointing device–a small trackball mounted to the rear of the center console–to enable either the pilot or copilot to move to different points on the map display and to alter the planned track, waypoints and so on. Most of the testing has been carried out using one pilot, with a safety pilot carried only for night flights.

“After our report is prepared, we will work to see how best to develop the equipment intended for the production version, within certification constraints,” said Bouheret. “In parallel, we will also work with the DGAC to develop the regulations required to certify this type of helicopter to fly IFR at low altitudes. Finally, we have to address
the international market, and for that the debate goes to ICAO. That’s where it gets difficult–the technical part is relatively straightforward in comparison. We will start the ICAO process about this time next year. I anticipate certification some three years from now and first customer deliveries before the end of 2007.”

Eurocopter said its HTT trials have been making steady progress for more than two years now. There is still a long way to go before 19-seat rotorcraft are in a position to replace 19-seat turboprops on hub-and-spoke airline operations, thus freeing up landing slots for jetliners. However, the technology is now in place and, in a novel departure, regulators and airport authorities are being let in on the secret, in time to consider them in future infrastructure pla