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US Airways advanced navigation: why RNP?


US AIRWAYS is one of a growing number of carriers that are preparing aircraft and flightcrews to benefit from NextGen's precision-based navigation procedures.

The Federal Aviation Administration notes that as of 10 March, 1,850 aircraft had been approved for RNP SAAAR/AR (special aircraft and aircrew authorisation required/authorisation required) procedures in the US national airspace system, compared with 1,000 aircraft in December 2010.

Aircraft operators wanting to enter the world of NextGen can now find guidance on the subject in the International Civil Aviation Organisation's PBN Manual, the European Aviation Safety Agency's AMC20-26 and the FAA Advisory Circular 90-101: Approval Guidance for RNP Procedures.

The operator's desired approach(es) must be designed, and its aircraft fitted with navigation equipment and certificated by a regulatory authority. A flight operational assessment is also required to demonstrate the capability of both aircraft and crew to fly the procedures.

The aircraft's navigation systems must be capable of using GPS or other multimode navigation receivers, an inertial reference system, a flight management system, and barometric altitude sensing equipment. Users should be able to create and follow, through the flight management system, a navigation trajectory through space, depict the aircraft's progression on the path, and have the monitoring and alerting capability to warn the crew of any degradation of required navigation precision.


New-production aircraft have built-in RNP capability. Older examples require upgrades. Aircraft downtime and costs for upgrades vary greatly depending on the software and hardware requirements. The bill could be as high as $1 million for a 15-year-old aircraft requiring a multimode receiver, GPS receiver or updated FMS, says Airbus.

Regulatory authorities generally design "public use" RNP approaches that are available to all carriers. To design a "special use" approach, an operator would seek the services of an RNP design firm such as Airbus's Quo Vadis subsidiary, GE PBN Services, Jeppesen or Honeywell GoDirect. US Airways has designed its own procedures, however. It uses Terminal Area Route Generation and Traffic Simulation software, also used by the FAA to design terminal airspace procedures.

US Airways' senior vice-president of flight operations, Ed Bular, says the RNP approaches will "allow use of precision RF [radius to fix] legs which can reduce distance flown, fly around obstacles and, in some cases, avoid noise-sensitive areas".

Bular adds: "It doesn't take much to create substantial savings. If we just save one mile on all of our mainline flights at Charlotte, we can save $1.7 million annually at $2.10 per gallon and reduce CO2 emissions by 3,000t. We have seen many RNP procedures reduce distance by more than one mile."

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