Air Berlin broadens use of RNP

Berlin
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Air Berlin plans to roll out required navigation performance (RNP) procedures to more airports and aircraft types as it begins to see the performance benefits offered by the technology.

The German carrier has configured around three-quarters of its almost 60-strong Boeing 737 fleet for the satellite-based approach and departure routings, and has been using the RNP authorisation-required (RNP-AR) system for flights to and from Innsbruck, Austria, since earlier this year.

Approval is also being sought to employ the technology - which allows curved precision approaches - at Salzburg airport from January, says Captain Marc Altenscheidt, head of Air Berlin's Boeing fleet. This will facilitate landings on the Alpine hub's runway 33 from the southeast via an S-shaped approach path between mountains of up to 9,850ft (3,000m).

Altenscheidt adds that the airline is also in discussions with Greece's Hellenic Civil Aviation Authority and Spanish air navigation service provider AENA to introduce RNP procedures for island destinations, which can be difficult to reach in marginal weather. Landings in Las Palmas, in Spain's Canary Islands, for example, require visual meteorological conditions for the final approach.

RNP allows an airline to mitigate the risk of delays or diversions, but can also create other benefits, such as lower noise and fuel consumption.

Innsbruck's runway 26 is set up with a localiser and distance measuring equipment (DME) for instrument approaches. Due to mountains peaking around 9,000ft east of the airport - the site sits at an elevation of 1,900ft - the localiser course (254°) is offset from the runway heading (259°), with pilots having to make a 5° right turn around 1.5nm from the runway threshold.

The descent begins at an altitude of 9,500ft around 19nm from the runway, with aircraft following a 3.7° glide profile. While the respective data is stored in the aircraft's flight management system, Altenscheidt says that pilots nevertheless need to actively manage the descent.

The steeper approach necessitates early extension of flaps and landing gear which, in turn, lead to higher noise and fuel consumption as more power is required from the engines.

While visibility needs to be at least 3,700m for such a localiser/DME approach, the cloud base must not be lower than 3,400ft. Decision height is 1,500ft.

If the pilots cannot see the runway at that point - around 3.4nm from the threshold - they have to initiate a missed approach procedure with a 200° left turn and climb out of the valley in the opposite direction.

The alternative RNP procedure, allows an aircraft to follow a more northerly track (246°) along the river Inn valley, whereby aircraft turn onto the runway heading 3.7nm from the threshold. This follows a 3.5° glide path, which allows extending flaps and landing gear closer to the airport.

For a missed approach, pilots can continue flying westbound through the valley and make a 215° left turn at higher altitude, before climbing out of the valley in opposite direction. The cloud ceiling during RNP approaches can be as low as 2,600ft, while visibility is reduced to 2,400m.

For RNP departures, the visibility can be as low as 300m, with no limitation in terms of cloud base. This gives RNP-authorised airlines an advantage over carriers operating under conventional regulations, which require visibility of at least 1,500m and a 3,400ft cloud ceiling.

RNP operations for runway 08, for which there is currently only a visual approach procedure, is being assessed by Austro Control.

Air Berlin has so far equipped only its new 737s with the necessary FMS software module and navigational database, which need to be validated by the regulator for each individual airport. As the airline's Airbus A320s are currently not deployed on routes to Innsbruck and Salzburg, the modification and crew training was not necessary. However, Altenscheidt says that the airline is evaluating the possibility of extending RNP operations to its A320 fleet.