More Operators Gain Access to RNP AR Approaches

 - August 1, 2022, 3:19 PM

Now that more aircraft come from the factory with avionics suitable for flying the latest RNAV RNP instrument approach procedures that require special authorization, pilots and operators might wonder how they can gain access to these approaches.

RNP-AR offers significant benefits; at terrain-challenged airports where it is available, RNP-AR can allow a safe, comfortable arrival in much lower weather conditions versus having to divert to an alternate because the ordinary instrument approach has much higher minimums.

As more business jets come equipped for required navigation performance (RNP), the FAA has made it easier to take advantage of RNP-AR (authorization required) approaches, which require special pilot training and operator approval.

Many of the RNP-equipped jets have Honeywell NG flight management systems (FMS). Since 2007, Honeywell has offered a consultancy service to help operators gain RNP-AR approval, including the required letter of authorization (LOA), developing SOPs, checklists, and minimum equipment list (MEL) updates, and supporting nav database validation.

What makes RNP possible is the precision available from modern satellite navigation and augmentation systems. If an aircraft can fly a consistently narrow path, then an approach can be designed with sufficient obstacle clearance but to lower minimums and to runway ends that don’t accommodate traditional navaid-to-navaid or even waypoint-to-waypoint approaches. Missed approach procedures are equally able to follow more efficient paths, although aircraft are required to have inertial reference systems to provide a backup in case of GPS failure during a missed approach. These approaches require coupling to the autopilot.

As Honeywell explains in its RNP-AR video: “RNP-AR procedures are designed with a narrow linear obstacle containment area with only two times the required RNP with no secondary obstacle boundary and they may also include curved flight paths called RF legs in any segment of the procedure including the approach final segment.”

“This allows approaches to runways that historically haven’t had them due to obstacles or terrain,” said Jim Johnson, Honeywell senior manager, Flight Technical Services.

Examples of Honeywell-developed RNP-AR approaches include Aspen and Eagle, Colorado. At Aspen, the lowest Category C (which covers the typical business jets discussed here) minimums are 3,122 feet agl with a 6.59-degree glidepath. The RNP-AR approach offers a decision height of 537 feet and has a more comfortable 3.5-degree glidepath, which makes managing approach speed much easier. At Eagle, the decision height is 288 feet versus 1,790 feet.

“For Aspen, not only are the minimums much better,” Johnson said, “the glidepath is 3.5 degrees. The best approach today is a 6-degree glidepath. By nature that’s unstable. This provides a stable approach.”

Carey Miller, Honeywell senior technical sales manager, explained that during ice-inducing weather conditions, it’s much easier to keep power at a higher level to ensure proper heating of engine inlets and leading edges of flying surfaces with a less-steep glidepath.

More important, however, is that RNP-AR allows the design of approaches that guide the airplane to a low decision height right to the runway end at airports where the only alternative approach for using that runway would be a risky circling approach. At busy airports where non-RNP aircraft have to fly well away from the airport to slot into an approach procedure, RNP-AR-capable aircraft can be guided into shorter and more efficient approaches.

Southwest Airlines, for example, worked with the FAA to develop short-transition RNP-AR approaches to some Texas airports with three-mile RF legs to final, according to Johnson. “Otherwise you’re vectored seven miles out and seven miles in.”

Honeywell has been discussing with the Teterboro Users Group an RNP-AR approach to replace the risky ILS to Runway 6, circle to Runway 1 visual approach that is used in certain wind conditions. “We even put together a prototype and flew it,” he said, but although there is FAA interest, nothing further has developed. But this is a good example of how RNP-AR can help improve a risky approach.

There are about 400 RNP-AR approaches certified in the U.S., 50 outside the U.S., and Canada is working on 80-100 such approaches. Honeywell NG FMS-equipped jets certified for RNP-AR include the Gulfstream G450/G550, G500/G600, and G650; Embraer E170/E190; Hawker 4000; and Falcon 900EX EASy and 8X. Future certifications will include the Falcon 6X and 10X, Gulfstream G400/G700/G800, Pilatus PC24, and all new jets with Honeywell NG FMS.

“The majority of those approaches are FAA-developed,” Johnson said, but the Aspen and Eagle approaches were developed by Honeywell, working with an approved procedures developer, so these are private approaches available only for Honeywell database subscribers. One of the reasons these approaches aren’t available from the FAA is that they required an FAA exemption for higher missed approach climb gradients. At Aspen, the RNP-AR missed approach gradient is 452 feet/nm, well above the FAA’s 200 feet/nm standard. Not all business jets can meet the higher gradient,” he explained, and to be a publicly available RNP-AR approach, the majority of aircraft using it would have to be able to achieve that gradient.

To meet the requirements to fly RNP-AR approaches, operators can look to FAA Advisory Circular 90-101A. They will need to obtain a letter of authorization (LOA) under OpsSpec C-384. Of course, operators can do this process themselves, or work with Honeywell, which has long experience in RNP-AR approvals.

“It has become easier and more streamlined,” said Johnson. “We’ve done quite a few of these applications, and we have a good handle on what the FAA wants.” Honeywell can help an operator gain RNP-AR approval in about two to three months, he said.

The operator must have the LOA to gain access to the Honeywell nav database that contains the RNP-AR approaches. Once approved, the operator can fly RNP-AR procedures in the U.S. and internationally.

Pilots must undergo simulator training at FlightSafety International or CAE before the LOA will be issued. The approval allows the operator to use any of the RNP-AR approaches, including those outside the U.S. The only currency requirement is to fly at least two RNP-AR approaches during annual recurrent training. And one significant hump that used to deter business jet operators—the requirement to fly 100 approaches before gaining approval to fly to the lowest minimums—has been relaxed for business jet operators that don’t fly often to the same airports. Now the FAA requires approaches at 10 to 15 airports that the operator typically flies to, according to Honeywell.

Honeywell Flight Technical Services charges $10,295 per aircraft to help operators set up their procedures, checklists, and MELs then works with the FAA for the LOA. Once the LOA is issued, Honeywell provides the updated nav database with the RNP-AR procedures for an annual subscription fee of $6,496.