Avionics News February 2012 - 38

RETROFITTING FOR RNP
Continued from page 37

ment database and paper charts used for RNP operations and FAA approval of initial and recurrent training for pilots. Bob Lamond, National Business Aviation Association air traffic services director, estimates the cost of authorization – not including the avionics – at $90,000 per airplane. The process can take six-to-10 months to complete. The FAA doesn’t concern itself with dollar costs, but using an experienced RNP consultant can speed the process of assembling more than 300 pages of documentation in a typical application for authorization. The FAA declined to comment on the required page count. Obviously, the cost in terms of both time and dollars puts it beyond the range of all but the largest business jet operators – just 20 have achieved FAA RNP-AR authorization. To date, those operators are all flying Gulfstreams or Boeing Business Jets (executive variant of the B-737), but according to the FAA, applications also are currently being processed for Cessna and Dassault operators. RNP for the Little Guys The disconnect between the FAA’s goals for broad use of RNP in the U.S. airspace (part of an overall move to “performance-based navigation”) and the cost and complexity of the authorization process has caused a great deal of confusion. Both Lamond and Steinbicker said this is a result of a misunderstanding. RNPAR approaches are only intended for the most extreme cases and are comparable to instrument landing system
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category-II and III approaches, which carry similar restrictions. This leads to a natural question. If RNP-AR is equivalent to a categoryII/III ILS, what is the equivalent to a generic cat-I ILS flown regularly by operators in everything from airliners down to light piston singles? The answer from Bill Stone, Garmin avionics product manager: “Most people don’t realize general aviation is way ahead of commercial and military operators – GPS/WAAS sensors have

standard, and will not require authorization, beyond what is in the aircraft flight manual or supplement, according to Steinbicker. Steinbicker and Stone disagreed about what equipment would be required to fly an RNP-1 approach with RF. According to Steinbicker, the FAA expects any aircraft flying an approach with RF legs to have a flight director or roll-steering autopilot, as required by AC 20-138B. Stone countered it should be possible to hand-fly a

...To fly an RNP-1 procedure, the avionics, aircraft and pilot are required to maintain aircraft position within one nautical mile of the desired track 95 percent of the time, and, at all times, the pilot must be informed whether or not the avionics and aircraft are achieving the goal.

been demonstrated to meet RNP-0.3 requirements. In fact, an approach to LVP minimums is actually an RNP-0.3 procedure.” The FAA’s Steinbicker confirmed GPS with WAAS does indeed provide the monitoring and alerting functions required for RNP operations. What differentiates an RNAV(GPS) approach to WAAS-enabled LPV minimums from a true RNP approach is the absence of any radius-to-fix capability. But, Steinbicker said this may change. The FAA is investigating the possibility of adding RF to selected approach and departure procedures (possibly including some missed approaches) “where beneficial.” Those procedures would be to an RNP-1

curved approach path, and he added that Garmin is currently supporting research to demonstrate whether or not this works. Stone believes RF-enabled curved approach paths could offer a significant benefit in complex airspace, mentioning Hawthorne, Calif., White Plains, N.Y., and Frederick, Md., as examples. “If it turns out to be easy to fly, then it will be widely used,” Stone said. But, he expressed concern about the requirement to have a flight director. Stone isn’t the only one concerned about equipment requirements. Andy McDowell, director of airspace and airport services for Jeppesen, which is an FAA-approved RNP application con-

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Avionics News February 2012

Table of Contents for the Digital Edition of Avionics News February 2012