Flight testing is under way at Honeywell in Phoenix, Arizona, to develop precision approach procedures for helicopters, using differential global positioning system (DGPS) guidance.

Honeywell has teamed with Sikorsky and Universal Avionics to help the US Federal Aviation Administration develop terminal procedures (TERPS), providing helicopter operators with greater flexibility than under existing rules, developed for fixed wing aircraft.

A Sikorsky S-76B, equipped with a Universal UNS-1 flight management system and VHF datalink receiver, is flying precision DGPS approaches using the Honeywell/Pelorus satellite landing system (SLS). The helicopter, equipped with a Honeywell four axis autopilot, has been flown on fully coupled automatic approaches, says Dwight Schaal, technical manager with Honeywell Business and Commuter Aviation Systems.

Schaal says that the FAA plans to develop TERPS standards for three helicopter specific precision approach categories: H1, for hand-flown approaches using raw DGPS data; H2, for manual approaches, using flight director guidance; and H3, for automatic approaches.

H1 will be equivalent to a Category 1 instrument landing system, he says. H3 will allow the helicopter to be flown hands off to a decision height of around 50ft, (17m) while decelerating automatically to 15kt (25km/h).

Helicopter operators must follow the same instrument landing procedures as those for fixed wing aircraft, severely limiting flexibility in low visibility. "DGPS gives us the first real opportunity to take advantage of the unique capabilities of a helicopter," says Sikorsky test pilot Nick Lappos.

Source: Flight International