Runway designations

Runway designations change over time because the magnetic poles slowly drift on the Earth's surface and the magnetic bearing will change. Depending on the airport location and how much drift takes place, it may be necessary over time to change the runway designation. As runways are designated with headings rounded to the nearest 10 degrees, this will affect some runways more than others. For example, if the magnetic heading of a runway is 233 degrees, it would be designated Runway 23. If the magnetic heading changed downwards by 5 degrees to 228, the Runway would still be Runway 23. If on the other hand the original magnetic heading was 226 (Runway 23), and the heading decreased by only 2 degrees to 224, the runway should become Runway 22. Because the drift itself is quite slow, runway designation changes are uncommon, and not welcomed, as they require an accompanying change in aeronautical charts and descriptive documents. When runway designations do change, especially at major airports, it is often changed at night as taxiway signs need to be changed and the huge numbers at each end of the runway need to be repainted to the new runway designators. In July 2009 for example, London Stansted Airport in the United Kingdom changed its runway designations from 05/23 to 04/22 after dark.

Parallel Runway Designations

Situation

Several New Zealand aerodromes have parallel runways where there is a main sealed runway with a secondary parallel grass runway. The aerodromes include one main international aerodrome (Christchurch), a number of regional certificated aerodromes, and some unattended/non-certified aerodromes (eg Ardmore).

The Issue

ICAO Annex 14 requires that a runway designation marking shall be provided at the threshold of paved runways and recommends the same for unpaved runways. Annex 14 also states that, where provided, the designation marking shall consist of a two-digit number and, for parallel runways, be supplemented with a letter “L”, “R” or “C” (left, right or centre), as appropriate.

In New Zealand, not all parallel runways use the Annex 14 convention mainly due to one runway being sealed and the other grass. It has also become common practice to only mark the sealed runway at the threshold with the grass runway not having a specific runway designator marking. If the grass runway is marked, it does not generally include the supplementary “L”, “R” or “C”.

Airways New Zealand has noted that at several controlled aerodromes there has been inconsistent naming of parallel runways and consequently inconsistent use of radio phraseology when clearing an aircraft to land. At some aerodromes, the term “runway” is used for the sealed runway and “grass” for the parallel grass runway. The problem with this is that the grass strip is itself a “runway”, so it is open to misinterpretation. This is unsatisfactory from a human factors point of view and can lead to an incident. At other aerodromes the terms “seal” and “grass” are used.

The CAA Position

Parallel Runways with the Same Physical Surface

Aerodromes with parallel runways of the same physical surface must use the letter supplement “L”, “R” or “C” as appropriate. The aerodrome operators must ensure the correct runway designation marking including letter supplement is positioned at the threshold of each runway in accordance with Advisory Circular AC139-6 or AC139-7 as appropriate. Radio phraseology including the runway designator and letter supplement must be used by pilots and air traffic control (ATC), if applicable, in accordance with AC91-9.

Parallel Runways with Different Physical Surfaces

Aerodromes with parallel runways that clearly have different physical surfaces do not need to use the “L” or “R” letter supplement. This is dependent on the aerodrome layout, but if no letter supplement is used, then pilots and ATC radio phraseology must include the prefix "seal" or “grass” with the runway designator in accordance with AC91-9. The aerodrome operator should still ensure the correct runway designation marking is positioned at the threshold of each runway in accordance with Advisory Circular AC139-6 or AC139-7 as appropriate, but without the letter supplement. It is recognised that the marking of grass runways is difficult and a proposed change to the aerodrome Advisory Circulars will allow for different marking methods.

Part 172 – Air Traffic Control

To ensure a consistent and unambiguous service at aerodromes with parallel runways with different surfaces, ATC clearances are to include the prefix “seal” (RWY designator), or the prefix “grass” (RWY designator), as appropriate, in accordance with AC91-9. However, at aerodromes with one main sealed instrument runway, and a parallel much shorter grass runway, where the aircraft concerned can only use the sealed runway, the use of the prefix “seal” may be omitted.

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The following Advisory Circulars are being updated to reflect the CAA position:

AC139-6 Aerodrome Standards and Requirements: All aeroplanes conducting Air Transport Operations - All Aeroplanes above 5700 kg MCTOW

AC139-7 Aerodrome Standards and Requirements: Aeroplanes at or below 5700 kg MCTOW - Non Air Transport Operations