Notices to Airmen (NOTAM)

Photo: Mercedes Benz

Figure 18.2 Snow clearance

18.31 Wheel Braking On Wet Runways. The inherent friction characteristics of a runway surface deteriorate only slowly over a period of time, but the friction of a runway surface and thus the braking action can vary significantly over a short period in wet conditions depending on the actual depth of water on the runway. Also, long term (six monthly) seasonal variations in friction value may exist. The consequence of combination of these factors is that no meaningful operational benefit can be derived from continually measuring the friction value of a runway in wet conditions. In the context of these paragraphs a ‘wet runway’ covers a range of conditions from ‘Damp’ to ‘Flooded’ as described below. It does not include ice or runways contaminated with snow, slush, or water associated with slush. Paved runways of 1200 m and longer at civil aerodromes licensed for public use have been calibrated, to ensure that the friction characteristics of a runway surface are of a quality to provide good braking action in wet conditions. The presence of water on a runway will be reported on R/T using the following descriptions:

Aeronautical Information Service (AIS) 18

(AIS) Service Information Aeronautical 18

18.32 Interpretation. When a runway is reported as ‘DAMP’ or ‘WET’ pilots may assume that an acceptable level of runway wheel braking friction is available. When a runway is reported as having ‘WATER PATCHES’ or being ‘FLOODED’ braking may be affected by aquaplaning and appropriate operational adjustments should be considered. “Water patches” will be used if at least 25% of the runway length is covered with standing water. When a runway is notified as liable to be slippery when wet, take-offs or landings in wet conditions should only be considered when the distances available equal or exceed those required for a very slippery or icy runway as determined from information in the aeroplane’s Flight Manual. At military aerodromes in the UK, runway surface conditions will be described in plain language, and, where a braking action measuring device has been used, braking action will be described as good, medium or poor.

ASHTAM

18.33Purpose. Volcanic ash cloud presents a significant hazard to turbine engine aeroplanes. Timely warning of the presence of ash clouds or the possibility of an ash cloud existing is vital to safe operations in areas where volcanic activity is common. Information concerning an operationally significant change in volcanic activity, a volcanic eruption and/or volcanic ash cloud is reported by means of an ASHTAM.

18.34Description. The ASHTAM provides information on the status of activity of a volcano when a change in its activity is, or is expected to be of operational significance. This information is provided using the volcano level of alert colour code. In the event of a volcanic eruption producing ash cloud of operational significance, the ASHTAM also provides information on the location, extent and movement of the ash cloud and the air routes and flight levels affected. The maximum period of validity of an ASHTAM is 24 hours. A new ASHTAM must be issued whenever there is a change in the alert level.