WestJet is first airline to take advantage of let-downs that provide accuracy by being tailored for specific users

Transport Canada has cleared WestJet to carry out flight management system (FMS) -guided airport approach procedures using area navigation (RNAV) capabilities certificated to record accuracy levels.

The airline, with its Next Generation Boeing 737 fleet, has been working with Seattle-based RNAV specialist Naverus to develop approved GPS satellite navigation-dependent approach procedures that can be flown to required navigation performance (RNP) standards better than 0.1nm (185m) lateral track tolerance.

WestJet has just begun flying into Kelowna in mountainous western Canada using the standard-fit 737NG FMS and navigation hardware to achieve the RNP standard. The airline expects to implement the procedure at 17 more Canadian airports, with Abbotsford probably the next.

The unique aspect of this programme, says Naverus's business development manager Stew Chaplin, is that Transport Canada has delegated the approach design task to Naverus working with Boeing and flight management computer (FMC) manufacturer Smiths Aerospace to ensure the procedure can be performed safely within the aircraft's and its systems' performance capability.

Clearing Naverus to do this work has enabled the procedures to be designed and submitted for clearance more quickly than Transport Canada's resources would allow, and Chaplin says Naverus expects to continue working with WestJet to design more than 90 RNP RNAV approaches into almost all 24 Canadian destinations that the airline serves.

WestJet's 737NGs have twin FMS and dual GPS sensors, which is normal - though not compulsory - for the type, but necessary for RNP. In addition, the Smiths FMCs have particular capabilities that make the RNP achievable to 0.1nm and provide greater flexibility in approach design, including the ability to fly fixed-radius arcs, says Chaplin.

Navigation input is from non-augmented GPS and the inertial navigation system. Flight dispatch includes a real-time update of GPS signal quality at the destination airport, which determines the RNP precision to which the aircraft can fly.

Head-up displays are not necessary, and the three-dimensional trajectory can be flown manually or by autopilot, with vertical trajectory defined by barometric vertical navigation and FMC-coded flight path constraints.



Source: Flight International