AN ALASKA AIRLINES Boeing 737-400 has been flown successfully on satellite-navigation (satnav)-based instrument approaches to a 300ft (90m) decision height at Juneau, Alaska without using any ground-based navigation aids.

The pioneering flight was undertaken by Boeing and Smiths Industries as a proof-of-concept demonstration to the US Federal Aviation Administration and Alaska Airlines. The ultimate aim is to certificate a new satnav instrument approach to Juneau.

Unlike previous tests with modified flight-management systems (FMS), there was no use of an instrument-landing or microwave-landing systems for lateral guidance.

For the tests, the aircraft's Smiths dual FMS was upgraded with new software. The two independent flight-management computers (FMCs) were provided with their own input from a Honeywell global-positioning-system (GPS) receiver. The tests proved that the system "...worked with a sufficient degree of accuracy that either system can get you in or out of there with safety", says Smiths Industries senior engineer, Dick Winkel.

No differential GPS (DGPS) ground station was used, the trials relying on overhead signals only.

The procedure was based on a required navigation performance (RNP) of 0.5km (0.3nm), and designed to be safely flown if the actual navigation performance (ANP) was equal to, or less than the RNP. The ANP was monitored by the FMCs. Several approaches were flown, including missed asymmetric approaches with one engine at flight idle to simulate one engine out.

Source: Flight International