Flysafe - weather hazards

About 20 to 30% of worldwide air accidents are related to adverse weather conditions.

In Europe approximately 22% of air traffic flow management delays are due to bad weather. Such delays have a considerable cost for both airlines and users. The weather costs in Europe will be estimated within the project and a reduction of up to 40% in such costs will be sought through the new FLYSAFE systems. Besides this, airlines also have to pay significant insurance fees for injuries caused by adverse weather, especially turbulence - such costs could likewise be reduced.

Weather hazards will be addressed by work package 2 of the FLYSAFE project. Work here will develop the capability to provide data on all meteorological hazards, during all phases of flight, to the Next Generation Integrated Surveillance System to be designed within the project. Preceding this development, studies will be performed to quantify the sensitivity of the aircraft to the various hazards, including physical, engineering, operational and economic sensitivity.

This work package will also address institutional issues related to both the merging of European weather observation and forecast systems in order to provide integrated consistent information to the 'Single European Sky', and the allocation of frequencies between ground and aircraft for transmission of digital high-rate information. Finally, optimum use of weather information by all everyone in flight and on ground will be raised through co-ordination with concurrent integrated projects.

The key objective of FLYSAFE is to provide the pilot in real-time with the most recent and comprehensive information on adverse weather for the aircraft's immediate environment and flight ahead to the final destination. The meteorological phenomena of physical sensitivity are:

Wake vortex encounters close to the ground can lead to aircraft crashes and in cruise they are becoming more frequent with the development of reduced separation vertical minima (RVSM). The effect of wake vortices depends mainly on the weight of the aircraft creating them and the weight of the affected aircraft. In approach and landing for example, certain separation limits exist dictating the capacity at busy airports.

The transport and decay of wake vortices, on the other hand, which strongly affects the actual possible separation, depends on the particular weather conditions. As the prediction of terminal area wake vortices have been adequately covered by other EU projects, FLYSAFE will focus on the development of upper-level wake vortex forecasts and the combination of different tools to increase forecasting accuracy of wake vortex behaviour. Both RVSM and terminal area wake vortex forecasts will be covered.

CAT encounters are most dangerous as they cannot be sufficiently detected by current onboard sensors. The Met Office's nowcasting model WAFTAGE will be exploited to provide short-range forecasts of wind shear and other parameters of importance for predicting clear air turbulence.

As much CAT is caused by thunderstorms at lower level, the Weather Intelligence Management System will take predictions of thunderstorms as an input. A climatology of jet-stream induced clear air turbulence for the North Atlantic and North Pacific flight corridor will be established. The capability of medium-range weather forecast systems to forecast such induced CAT will be analysed and a long-range climatology of most probable regions of jet-induced CAT together with thresholds of weak, moderate and severe CAT events will be provided to the Weather Information Management System.

In-flight icing mainly affects the performance of the aircraft. Increased weight and a changed wing shape due to ice accretion adversely affecting the airflow around the wing can cause:

Besides that, ice deposition on small surface parts like propeller blades or the freezing up of sensors like the pitot tube can lead to significant problems, including loss of communication or wrong decisions due to spurious sensor values. Finally, ice induction into the engines can cause major damage to the aircraft, resulting in high repair costs or even fatal accidents. This component of the Weather Intelligence System will consider freezing rain and freezing drizzle as well as icing in convective and stratus clouds. Information on both the location and severity of the icing hazard will be provided with a spatial resolution of ~7 km for the cruising level and ~2 km for the airport terminal area.

In general, thunderstorms contain all of the weather phenomena mentioned above. They are considered a serious hazard. Though most aircraft are hardly affected by lightning strikes, the wind shear and turbulence can cause major stability and control problems. Due to the strong updraughts, supercooled liquid water and thus ice accretion can occur at levels normally considered unlikely to produce icing. Finally, hail can grow to sizes where it can seriously damage the aerofoil of an aircraft. The weather information system will provide information about thunderstorms for both en-route flights and the terminal area with the same spatial resolutions as the icing above, with input from various sources such as lightning detection tools and mapping systems.

Volcanic ash

Photo courtesy of Sigurjón Sindrason (sigurjon@ok.is)

Volcanic ash can seriously affect engine performance. Volcanic ash forecasts are currently provided within the Significant Weather Charts of the World Area Forecast Centre (WAFC). The hazard of volcanic ash will be covered within the routine weather data set, as will visibility and other mechanisms causing wind shear.

For further information relating to Met Office involvement in this project, please contact aviation@metoffice.gov.uk.