Honeywell last month gave the first flight demonstrations of an RNP (required navigation performance) approach being developed at Morristown Municipal Airport (MMU), located just a stone’s throw from the company’s global headquarters in New Jersey. Flown in a Honeywell Gulfstream G450, the procedure is significant for being among the first created for a general aviation airport and, Honeywell noted, will serve as the basis for RNP operational approval of its G450 and G550.
Honeywell has teamed with Gulfstream and Jeppesen on the project, which seeks to add an RNP SAAAR (special aircraft and aircrew and authorization required) approach featuring a gentle fix-to-radius (RF) turn to the final approach course to Morristown’s Runway 5. RNP procedures allow appropriately equipped aircraft to shoot complex, curved approaches with needle’s-eye accuracy to minimums thanks to the technique’s precise path-keeping capabilities. And because RNP uses GPS and airborne inertial sensors for navigating, ILS and VOR ground stations aren’t needed to develop new RNP procedures. Morristown has an ILS approach to Runway 23, but no precision approach to Runway 5.
A handful of airlines have started flying RNP procedures at a number of U.S. airports, but by and large such approaches have been slow to emerge. The FAA is eager for their broader acceptance and adoption by airlines and business jet operators, judging RNP to be one of the key elements of the so-called next-generation air transportation system. “RNP will probably be the basis for air navigation in the United States for the next 30 years,” said Chad Cundiff, Honeywell vice president for crew interface products. So far 46 RNP approaches are in use around the country. The FAA hopes new procedures can be created and approved at a rate of about 25 a year.
SAAAR Approval ‘Intimidating’
But gaining aircraft and crew approval to fly RNP procedures involves meeting a complicated set of prerequisites, including simulator training, MEL revisions, validation testing and even an RNP SAAAR approach monitoring program that requires operators to track each approach they fly and submit monthly reports to the FAA. Advisory Circular 90-101, the FAA document that deals with RNP operator approval, emerged two years ago, but so far not a single business jet operator has gone through the laborious process of gaining RNP SAAAR qualification. “Frankly, the AC is intimidating,” Cundiff said.
The PlaneView avionics system in the G450 and G550 today is capable of flying RNP procedures to 0.3-nm accuracy, which is the threshold where a SAAAR letter of authorization is required. New Version 6.1 and 7.1 FMS software due out next year from Honeywell will provide even greater accuracy, down to 0.1 nm. Additional hardware upgrades including inertial reference system upgrades might be needed, but these are not common to all aircraft, Cundiff added. To fly the more accurate 0.1 RNP procedures, which offer lower minimums, the RNP SAAAR approval will also be required.
Gulfstream plans to provide assistance to operators seeking RNP SAAAR qualification by helping them prepare their compliance package and create, monthly reports. Mike Mena, director of advanced cockpit programs for Gulfstream, said RNP 0.1 capability initially will be brought to the G450 and G550, and then eventually made available across its entire aircraft line, even down to the G150 and G200. For retrofit upgrades in the GII, III and IV, hardware upgrades including new flight management systems and glass displays will be required, he added.
Jeppesen has signed an agreement with the FAA making it eligible to serve as a third-party designer of RNP procedures. The Rnav (RNP) Z Rwy 5 approach to MMU is the first by Jeppesen to obtain the FAA’s green light for qualification. But the approach demonstrated last month isn’t the final version of the one that will eventually appear in Jepp approach plate books and FMS nav databases, noted Todd Krawczyk, director of airway manual services for Jeppesen. “We’ll coordinate with New York Center to come up with the precise ground track for the approach so that we’re integrating with their flows in a way that makes the most sense for them,” he said. “For now, we’re merely proving the basic concept for the Runway 5 approach.”
One major benefit of RNP is that it reduces noise over populated areas by providing continuous descents and consistent paths over the ground. The procedures are also expected to save fuel and reduce emissions, as well as provide ILS-like landing minimums at airports that don’t currently have precision approach capability.
During the RNP demo flight, Honeywell chief pilot Ronald Weight let the G450’s autopilot do the flying while he discussed the crew interface. Vertical and lateral path indicators are shown on the PFD exactly as they would be when flying an ILS approach. A small box on the display includes two critical values, labeled RNP and EPU. The RNP value shows the guaranteed guidance tolerance. The EPU (estimated position uncertainty) shows the value of the total system error.
The performance required to fly an RNP route is specified in nautical miles. RNP 0.3 implies that the total system error should be no greater than 0.3 nm 95 percent of the time. As long as the EPU number stays below the RNP value, the crew can continue the approach. As soon as the number goes out of tolerance, the pilots must execute a missed approach. “But that should almost never happen,” Weight said.