What do the airports in the Gastineau Channel, AK; Gunnison, CO; and Christchurch, New Zealand, have in common? They all have incredibly demanding approaches. Unless conditions are ceiling and visibility unlimited, pilots cannot fly into these airports without the aid of RNP ARs.
Of course, airports in less exotic locations also have approaches that can test a pilot’s stick-and-rudder skills. John Kernaghan, a Trenton, NJ-based member of the NBAA’s Domestic Operations Committee, said approaches to Runway 06/24 at Trenton-Mercer Airport (TTN) offer their own challenges.
“We helped build an approach from the south of the airport, keeping the entire approach course within Philly's airspace. Several business aviation operators and airlines use it today.”
John Kernaghan NBAA Domestic Operations Committee
“Fifteen or so years ago, the runway was only served by an instrument landing system [ILS] to Runway 06, and a higher minimums, straight-in approach to Runway 24,” Kernaghan said. “The problem was the airport literally sits on the border of Philadelphia’s and New York’s (at the time) terminal airspace. In order to fly an approach to Runway 24, you had to talk to Philly, then to New York and Philly again before Trenton tower (requiring a lot of coordination).” Or a pilot could perform “an ILS to Runway 06 and then circle to 24, which was a low, high-banking maneuver – often in low visibility and high winds. It reeked of hazards.”
Now, with the advent of RNP AR, Kernaghan said, “we helped build an approach from the south of the airport, keeping the entire approach course within Philly’s airspace. Several business aviation operators and airlines use it today. It’s a great use of an RNP AR approach.”
“RNP AR approaches require the highest level of performance and capabilities of our FMS integration with the GPS and IRU.”
Richard Boll II Chair of NBAA’s Flight Technologies Subcommittee of the Domestic Operations Committee
Yet, as effective as they are, RNP AR approaches aren’t for everyone.
“RNP AR approaches require the highest level of performance and capabilities of our flight management system integration with the GPS and inertial reference unit (IRU),” said Richard Boll II, who chairs the NBAA Domestic Operations Committee’s Flight Technologies Subcommittee. “Very few business aviation aircraft are properly equipped and crews sufficiently trained to fly these approaches as they are currently applied.”
Experts: FMS-Guided Visual Approach Technology Enhances Safety
Advanced-RNP Capability Is Emerging
But business aviation is nothing if not innovative. As more advanced systems make aircraft flight decks more capable, new approaches that can fully take advantage of these capabilities have also started to spring up.
One of them is the Advanced-RNP (A-RNP) capability, which, as Boll explained, is not really an “approach” as much as a set of enablers that are used with existing RNP approach procedures. For example, RNAV (GPS) approaches in the National Airspace System (NAS) provide additional benefits to capable aircraft. These aircraft include avionic/RNAV systems that meet the functional performance requirements for an RNP AR approach, but without the burden of aircraft certification, flight crew training and qualification, as well as nav-database verification.
“In short, with A-RNP applied to an RNAV (GPS) approach or to an ILS approach with RNP approach segments, we can obtain many benefits from RNP AR approaches without the burdens that come with that approach qualification,” Boll said. “It is important to understand that there is no ‘A-RNP approach;’ we only apply the A-RNP enablers to other approach types. This is a big area of confusion in the industry.”
“With A-RNP, operators don't have to jump through all of the equipage and qualification hoops required to get some of the major benefits of RNP AR.”
John Kernaghan NBAA Domestic Operations Committee
Comparing A-RNP With RNP AR
“With A-RNP, operators don’t have to jump through all of the equipage and qualification hoops required to get some of the major benefits of RNP AR,” Kernaghan said. “Basically, the only operational difference between A-RNP and RNP AR is: With A-RNP, you can fly a curved course to get to the final approach course. However, that final course must be a straight-in approach to the runway.”
Of course, flying curved paths are nothing for today’s avionics and flight crews. However, there are still some defining requirements for the aircraft.
“As conceived by the International Civil Aviation Organization’s (ICAO) Flight Operations Panel and expressed in the ICAO Performance Based Navigation Manual, A-RNP allows operators of certain aircraft types to benefit from many of the features of the RNP AR approach,” Boll said. “For example: radius to fix (RF) legs, scalability on legs, parallel offsets, etc., in terminal environments where robust ATC radar surveillance is available. ATC radar substitutes for the need to equip with a backup navigation system like an IRU, so more aircraft can participate and benefit from features that have been only obtained through RNP AR approach. For example: the Denver International Airport (DEN) RNP AR approach supporting Established on RNP (EoR) operations.
“So, with A-RNP, RF legs with scalability can be added to the ILS and RNAV (GPS) approaches at DEN, and then a significant number of business aviation aircraft would be able to participate,” said Boll. “Basically, any aircraft that is RF-leg equipped could participate in these EoR procedures.” Non-EoR participating aircraft must extend farther out on the approach, expend more track miles, time and fuel before they land, compared to those that can remain on the EoR path, he said.
“These A-RNP enablers can be used at other locations as well,” Boll said. As an example, he mentioned New Jersey’s Teterboro Airport (TEB) ILS Runway 06 missed approach procedure. Boll said it may be possible to design a missed approach that avoids conflict with New York’s LaGuardia Airport (LGA) ILS Runway 13 approach. Currently, when in operation, the LGA Runway 13 ILS approach “effectively shuts down TEB for all but 10 minutes each hour.”
“A-RNP is intended to be used in major terminal airspace where robust ATC radar surveillance is available. Hybrid surveillance that uses GPS or ADS-B does not qualify.”
Richard Boll II Chair of NBAA’s Flight Technologies Subcommittee of the Domestic Operations Committe
A-RNP Isn’t RNP AR ‘Light’
While an approach using A-RNP offers many of the operational benefits of an RNP AR approach, both of our experts stressed that A-RNP is not a “light” version of a traditional RNP AR.
“A lot of people feel that A-RNP is slightly less capable than an RNP AR, but it is not that,” Boll said. “A-RNP is intended to be used in major terminal airspace where robust ATC radar surveillance is available. Hybrid surveillance that uses GPS or ADS-B does not qualify since these surveillance systems are affected by GPS loss, just like the aircraft’s navigation system would be.
“A-RNP requires a commitment from ATC to provide the monitoring part through the approach,” said Boll. “Again, it will get you to the final approach fix, and then it can be used from the missed approach point and beyond.”
“A-RNP is a tool that will allow different countries to develop simplified procedures that can get you into an airport where you typically could not get into without the help of radar and other services.”
John Kernaghan NBAA Domestic Operations Committee
As Kernaghan explained, it’s proving to be extremely beneficial because it provides enhanced capabilities without all the stringent requirements of RNP AR. The important part is that pilots know what their aircraft is capable of doing – radius to fix, scalability, offset, etc.
“It can greatly reduce track mileage while giving ATC the opportunity to put an aircraft on an approach from the other side of the airport so they don’t have to vector you to the final approach course. They can cut you loose, and you can fly a curved path into the final approach fix,” he said.
“It simply provides more functionality on an approach,” Kernaghan said. “As the NAV specs permeate through domestic and international approach building, A-RNP is a tool that will allow different countries to develop simplified procedures that can get you into an airport where you typically could not get into without the help of radar and other services.”
FAA Is Considering A-RNP Recommendations
The industry could start seeing more A-RNP enabled approaches in the near future, Boll said. The FAA’s Performance-Based Operations Aviation Rulemaking Committee (PARC) – a forum comprised of members of the aviation industry – submitted its recommendations for implementing A-RNP into the NAS two years ago. As of this writing, the FAA is reviewing those recommendations. “They were sound and easily achievable,” Boll said. “There will need to be buy-in and acceptance of responsibility for using ATC radar as a redundant navigation capability for GPS loss by ATC facilities that desire procedures using A-RNP. However, we do not see that as a roadblock.
“We are basically awaiting FAA’s acceptance of the PARC’s recommendation,” Boll said. “Once we have that, it is up to the ATC facilities, with industry collaboration, to begin implementing them at terminal locations.”
International Business Aviation Council Ltd.