BA trials precision navigation at Heathrow

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British Airways (BA) has commenced trials of a new approach procedure at London Heathrow Airport designed to explore the benefits of increased navigation accuracy and more-efficient descent manoeuvres.

During the six-month trial, BA long-haul Boeing 747 and 777 aircraft arriving before 06:00 will be given the opportunity to fly precision area navigation (P-RNAV) flight-paths and conduct a continuous-descent approach. Virgin Atlantic is also preparing to take part in the tests.

P-RNAV is a more precise variation of the ‘basic’ area navigation (B-RNAV) capability required of all aircraft operating within European airspace. B-RNAV enables an aircraft to follow a particular flight path to within a lateral accuracy of 5nm (9.2km) for 95% of the time. P-RNAV increases the lateral accuracy to just 1nm (1.85km).

Better flight-path tracking accuracy would allow airlines to operate more efficient approach and departure routes. This, in turn, would reduce noise footprints and emission levels in the vicinity of the airport. Eurocontrol is also keen to drive the introduction of P-RNAV procedures in terminal airspace because it will generate consistency in procedure design and execution, and a resulting safety benefit.

Use of P-RNAV at Heathrow will be combined with the introduction of continuous-descent approaches, a technique which allows aircraft to descend into the airport approach stream in a single, continuous manoeuvre.

Under normal operating procedures, a Heathrow-bound aircraft would be released from the holding pattern at a height of around 7,000ft; the subsequent descent would typically bring it over central London at about 3,000-4,000ft.

But aircraft using a continuous-descent approach would effectively be able to maintain a higher altitude during the earlier segments of their descent – cutting down noise – while the overall flight path would be more direct.

A spokesman for UK airspace authority National Air Traffic Services (NATS), which is helping to manage the trial, says: “It will reduce the fuel and noise penalty – but also the radio communication workload.

“If you’re following a complex approach there is a lot of dialogue between the air traffic controllers and the aircraft. In traffic capacity terms you can be constrained as much by the amount of instruction time on the radio as by the airspace itself.”

The trial will encompass off-peak BA flights arriving at Heathrow via the Lambourne holding point to the northeast of the airport; this is the normal routing for long-haul services arriving from the Middle East and Asia-Pacific regions.

A spokeswoman for BA says that the 747 and 777 aircraft involved in the tests are already equipped to carry out the procedure, so the only investment being made is in preparatory simulation and procedural training. Navigation will be undertaken using the aircraft flight management system (FMS).

BA air traffic management project manager for area navigation (RNAV) Kevin O’Sullivan says that procedures for the P-RNAV approach have been drawn up by the CAA’s Directorate of Airspace Policy, and adds: “These are coded into the normal navigation database as a procedure – like the standard arrivals and standard departures – using the FMS.”

O’Sullivan says that the aircraft achieves its navigation accuracy for P-RNAV using DME/DME input. Other navigation data – for example, from VOR/DME navaids or Global Positioning System satellites – can be used for P-RNAV and even an inertial reference system (IRS) can maintain the accuracy for a short time, although O’Sullivan says: “We could use the IRS but it drifts a fair bit; it’s not used as a primary source.”

While the P-RNAV trial will take care of the intermediate approach stage, he says that BA is “looking to get together” with NATS to examine even tighter navigation accuracy for final approach – taking the navigation tolerance down to just 0.3nm. If the plan takes shape an operational trial, probably on approaches into London Gatwick, could take place in six months to a year.