Honeywell offers Bendix/King avionics for TPs, light and medium jets with RNP futures

Availability of RNP terminal ops to all GA pilots means better access and safer, easier-to-fly approaches.

By Woody McClendon
ATP/Helo. Challenger 604, Bell 222/412, Eurocopter AS350B3

RNP-equipped aircraft can now access the tight corridor along the Potomac River that serves DCA.

Aviation technology is moving at a pace never before seen. For over 50 years the VOR/ILS system has guided pilots to the runway through sleet and rain times during which we learned to pay attention to its quirks which could kill us.

Early area navigation (RNAV) systems using VOR and DME were excellent tools for more flexible navigation. When GPS arrived it brought new versatility and accuracy that made VOR seem clumsy by comparison, its faults-line-of-sight signal, rigid position fixing and large areas of no coverage now more apparent.

GPS approaches were easier to fly, and soon became the norm at many airports, especially in larger jets with flight management systems (FMSs) with their programmed approach data. The push for a more efficient airspace system produced specific efforts to reduce the size of the "box" around each airplane via tighter position fixing, particularly in terminal airspace.

The accuracy of GPS-the chosen system on which the new airspace would be based was less than what was needed. Engineers developed a method of augmenting the base GPS signal to increase its accuracy significantly, and called it the Wide Area Augmentation System (WAAS) or, in Europe, European Geostationary Navigation Overlay Service (EGNOS).

With the rapid advances in GPS technology and onboard avionics that enabled aircraft to fly in "tighter" boxes with a high degree of accuracy and reliability, the concept of required navigation performance (RNP) came to the fore.

RNP and WAAS opened the door to a whole new era of pinpoint navigation, and better access to airports surrounded by dangerous terrain or jammed together in urban airspace. So far, more than 1000 WAAS enabled LPV approaches and almost 150 RNP approaches have been generated, approved and filed in the Jeppesen database.

Operator guidelines to implement RNP in their operations were also published. This new technology called required navigation performance, special aircraft and aircrew authorization required (RNP SAAAR)-was chronicled recently (Pro Pilot Feb 2009, pp 80-83) when Honeywell demonstrated it in its Gulfstream G550.

The airplane flew a precision path through the mountains, arriving at PSP (Palm Springs CA) from a direction that previously required a circling procedure threaded into a narrow valley. In the course of the demonstration, Honeywell described other RNP arrivals and departures through complex airspace which would reduce separation and also increase traffic.

Having seen "the newest thing," we wondered how it would trickle down to the rest of the airplane population the midsize and smaller jets and turboprops that are not equipped with high end FMS and inertial reference systems (IRS).

Honeywell VP Crew Interface Products Chad Cundiff describes the company's program to support that market, noting that the Bendix/ King Apex Edge and Honeywell Primus Apex "are well suited to serve the needs of GA operators."

FAA's new advisory circular AC90-105 defines an operational structure for RNP-based terminal operations using the less stringent RNP tolerances typical of the Primus Apex system. RNP SAAAR operations were first defined in AC90-101, intended for aircraft that were suitably equipped for the highest levels of RNP accuracy-RNP values in the 0.3-0.1 range.

Terminal procedures developed under AC90-101 offer the maximum benefit of this technology, feeding aircraft through tightly defined airspace corridors constrained by terrain, as well as major airports in close proximity to one another.

Aircraft not equipped for RNP SAAAR navigation do not have access to these procedures. Still, in between those aircraft equipped with the barest essentials for navigation and RNP SAAAR equipped aircraft a wide spectrum of aircraft are operating with some form of FMS and GPS. AC90-105 will define RNP operations for those aircraft.


RNP approach plate for PSP (Palm Springs CA) requires dual FMSs, dual autopilot, at least one inertial reference unit (IRU) and 2 pilots trained to SAAAR standards. While this procedure will not be available to lesser equipped aircraft, others will soon be in place that will accommodate turboprops and smaller jets.

The spectrum of RNP operations as defined in AC90-101 (and now AC90-105) spans 4 levels. The most advanced is less than RNP 0.3-the least, RNP 0.3 with much simpler equipped aircraft. The most advanced requires dual FMSs, dual autopilots, dual GPS receivers and at least one IRS-the least requires a single GPS receiver and a single FMS, no autopilot and no flight director.

Clearly, aircraft equipped with the latter will have access to the fewest RNP-based operations-however, once the RNP-based airspace system is fully defined, they will have some access to that airspace.

New RNP SAAAR procedures are being added to the system every day, driven by operators' needs for better access to destinations like ASE (Aspen CO), SUN (Hailey ID) and TEB (Teterboro NJ)-the first 2 constrained by mountainous terrain, the third by heavily congested airspace. Operations under AC90-105 will require in most cases a separate group of approaches.

RNP SAAAR makes abundant use of radius-to-fix (RF) segments-curved flightpaths that thread challenging terrain or airspace restrictions between 2 defined fixes. The least sophisticated level of AC90-105, labeled "basic," cannot track RF legs, limiting access to RNP approaches using them.

In the "advanced" level in AC90-105, some maneuvers using RF legs are permitted, allowing appropriately equipped operators access to a broader spectrum of RNP approaches.

What, then, can operators of non-SAAAR-equipped aircraft expect from avionics vendors so they have access to some RNP-defined airspace? When will it be available? And at what cost? Cundiff says, "Honeywell already has available GPS and FMS products that will allow operators access to the 'basic' level (Appendix 1, AC90-105).

And we're working on enhanced products that will serve the needs of operators wishing to be approved for the 'advanced' level (Appendix 5, AC90-105)." He continues, "Also, in a manner similar to our Go Direct Services with RNP SAAAR, Honeywell will offer technical assistance to our customers in configuring their aircraft to comply with AC90-105, and in securing approval to operate in the RNP environment."

Apex Edge series consists of 2 main components-the KFD840 primary flight display (PFD) and the KSN770 multifunction display (MFD). Both are large flat-panel displays featuring brightly-colored, near-3D images of terrain, data in graphic formats, systems management advisories, navigational situation and warning functions.



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