A number of key steps, including certification, are required to start using EGNOS-based landing procedures in aviation, the so-called LPV approaches. Two experts speak about these and other issues in the drive to put EGNOS to work for aviation.
Pierluigi Parente directs AgustaWestland activities supporting the development of ground and airspace infrastructure, to widen and improve the efficient use of helicopters. He contributes to analysis, research and evaluation and supports the development of rotorcraft satellite-based navigation. He also keeps track of regulatory changes with respect to infrastructure and rotorcraft operations.
Parente considers EGNOS a key source of added value, allowing general aviation aircraft and rotorcraft to operate in small airports, heliports and in remote locations (helipads) in unfavourable weather conditions with limited need for ground infrastructure.
Michael Erb is the managing director of the Aircraft Owners and Pilots Association (AOPA) in Germany. He started flying in 1992 as a private pilot and ultimately obtained his instrument rating and Commercial pilot's licence. He has flown SBAS approaches in the United States and has accumulated 500 piloting hours, mostly with Cirrus SR-20/22, Diamond DA40 and Cessna 172 aircraft.
Both Parente and Erb know what it takes to obtain EGNOS certification and both expect EGNOS to play a key role in ensuring safety and efficiency in general aviation, in spite of an evolving regulation and certification framework.
Different worlds: the European Union and the United States
Erb and Parente agree that EU and United States strongly differ in terms both of technological maturity and the certification process. Considering technological maturity, Parente says, “While in the United States' WAAS has been in service for almost 8 years, EGNOS was approved for aviation only in March 2011, and everything is very new here”.
As EGNOS entry into service for aviation was granted very recently, the use of EGNOS-based LPV approaches is still limited in the EU. As for the certification process, in the United States private owners can quite easily obtain certification for their own aircraft, while in the EU the role of manufacturers is more relevant, because a lot has to be done with relevant regulatory authorities (EASA).
The picture in United States
According to Dr. Erb, “Flying with SBAS approaches in the United States is not a big deal, while in Germany it is not possible yet to fly using EGNOS LPV approaches, because we still don’t have any. At the moment, in Germany, EGNOS can be utilised en-route and for Baro-VNAV approaches but it cannot be utilised for LPV approaches.”
In the US, the Federal Aviation Administration (FAA) foresees an owner-centred procedure. “In the States, the owner of an airplane or helicopter can contact a maintenance centre and ask for an SBAS-compatible update of the on-board avionics system. This action starts a quick certification process with the FAA that involves that nspecific aircraft. In some cases, the owner can get the certification to use SBAS”, says Eng. Parente.
This framework, combined with almost a decade of experience in managing WAAS procedures at the FAA, local airports and maintenance centres, results in a regulatory-friendly environment for owners and pilots. “In the US it is sufficient to have an aircraft equipped with a certified receiver for SBAS. Historically the most popular devices were Garmin 530 and 430 units, now replaced by the GTN750 and GTN650 models," Erb explains.
"The 530 and 430 are the most popular in the general aviation market, and when they have the 'W' versions, 530W and 430W, are certified for flying LPV approaches. You just need to have the certified receiver and follow the instructions on the manual. You don’t even require a flight instructor. You simply have to try the approach in good weather conditions first, before flying with bad weather."
Work in progress in the EU
In Europe, the approach is different: usually it is the manufacturer that pushes to certify its new equipment. According to Parente, this process approach has some advantages. "Once the process is complete," he says, "EGNOS certification is valid for the whole fleet of the certified model. At AgustaWestland, we are currently certifying the EGNOS-based LPV capabilities of our rotorcraft. Then the model, not one particular helicopter, will have airworthiness certification to perform LPV approaches.”
As the definition of requirements and certification processes by EASA is still in progress (for example, Acceptable Means of Compliance (AMC) 20-28 are still in the Notice of Proposed Amendment (NPA) phase), it is still difficult for individual owners to obtain EGNOS certification for their own aircraft.
“In theory," explains Parente, "not only manufacturers can obtain EGNOS certification via a Supplemental Type Certificate (STC) procedure. But the approval of the technical design of the installation on their aircraft is not easily granted by EASA and it is definitely not cost-effective for the private owner”
The AugustaWestland experience
Parente provides a very clear overview of the key prerequisites necessary to enable a pilot to land with EGNOS, by using an approach with vertical guidance (LPV), also known as an APV SBAS approach, at a specific airport:
- The relevant flight procedures should be available in the airport or heliport: “For LPV approaches," he says, “you can think of these procedures as 'virtual rails' in the sky.”
- The necessary equipment needs to receive airworthiness certification by EASA or by the National Civil Authority. “Technical compliance of the aircraft's avionics should be certified and the aircraft itself must meet the required technical standards”, explains Parente.
- The operator should obtain the operational approval by national civil aviation authorities by showing that he is able to perform LPV approaches. “However”, suggests Eng. Parente. “You should consider that operational approval is required for precision approaches such as LPV, while the requirements for en-route usage of EGNOS are lower”.
In this process, the role of the rotorcraft manufacturer is of key importance: not only is it active in the operational and airworthiness certification process, but it develops flight procedures for experimental activity. The aim is to suggest improvements to relevant regulatory authorities, related in particular to rotorcraft flight procedure designs.
EGNOS benefits and the importance of building momentum
Erb and Parente are both certain that EGNOS can deliver huge benefits to general aviation. “With SBAS you have the opportunity to descend with vertical guidance right to the threshold of the runway, where there haven’t been any procedures before. You simply establish the proper path, like with an Instrument Landing System (ILS), and you fly down with a constant descent to the runway, which makes the flight much easier and much safer”, says Erb.
Parente explains, “Potorcraft instrument flight rules (IFR) operations are dependent upon weather conditions. Although there are many IFR-certified rotorcraft, there is an important limitation on their operations, as they are forced to use the navigation and approach procedures and facilities dedicated to fixed wing aircraft, therefore being penalized for the often incompatible flight profiles of the two categories.
"Today EGNOS provides a wide range of navigation and approach solutions, all based on the accurate satellite navigation capability. This can improve airport/heliport accessibility and rotorcraft integration without interfering with fixed-wing aircraft traffic.”
In this scenario, EGNOS, combined with ICAO design criteria for rotorcraft instrument approach procedures, is a key factor in the development of rotorcraft IFR capabilities and will be invaluable to rotorcraft operations, granting a high level of operational flexibility and flight safety.
“A huge advantage of EGNOS," Parente adds, "is that it allows precision approaches similar to ILS virtually everywhere, with a very limited need for ground infrastructure. This feature is what interests the most general aviation and rotorcraft operators. In Europe, in fact, there are a multitude of small airports that are not equipped with advanced radio navigation services, because they are too expensive.”
At the same time, both aircraft owners and manufacturers are important players in accelerating the process of diffusion of EGNOS-based certifications and procedures. “I’m sure," says Parente, "that European Regulatory Authorities are making good use of the know-how cumulated by manufacturers, in order to complete the definition of requirements and specifications.
"At the same time, pressure by pilots and aircraft owners to have EGNOS approaches available will drive more and more airports to create the necessary flight procedures, as happened eight years ago in the United States.”
Erb completely shares this view. “What is required now is to bring LPV procedures down to the runway. General aviation pilots are very interested in having these procedures published and are pushing for it, and we are seeing some movement. In France, Switzerland and in the Channel Islands, this has already been performed successfully. In the future, many others will come onboard, and I assume that in five years this will become a standard everywhere.”
1. ICAO Publications
2. ICAO Flight Procedures
3. EASA AMC 20-26 - Airworthiness Approval and Operational Criteria for RNP Authorisation Required (RNP AR) Operations
4. EASA AMC 20-27 - Airworthiness Approval and Operational Criteria for RNP APPROACH (RNP APCH) Operations Including APV BAROVNAV Operations