Description

Of all things which influence the safety of flight, the weather - the characteristics and behaviour of the Earth’s atmosphere - is the most uncertain and influential (either directly or indirectly).

Aviation Meteorology

The following can have a direct and indirect influence on flight safety (note: this list is not intended to be exhaustive):

• Turbulence associated with convective activity (for example, thunderstorms), terrain (for example, the movement of air masses over mountains), jet streams and the interaction between air masses (for example polar fronts and associated dynamics), can be significant enough to cause structural damage to aircraft.
• Icing: Ice Formation on Aircraft can alter the aerodynamic characteristics of an aircraft and cause damage to or loss of function of the engines and seriously affect the performance of an aircraft. The article Aircraft and In Flight Icing Risks discusses the commonly-encountered issues whilst high level ice crystal icing of turbine engines is a recently-identified and improperly understood phenomenon which occurs outside the normal icing envelope. Ice may form on aircraft whilst they are on the ground prior to flight and this must be removed and any further accretion on the airframe prevented by the Aircraft Ground De/Anti-Icing so that any aircraft is free of ice deposits at the point at which it gets airborne.
• Reduced visibility, associated with cloud, mist, fog, or sand storms, can make safe flight difficult or even impossible, even with the help of technology (Instrument Landing System (ILS), weather radar, synthetic vision systems, etc)
• Surface contamination; standing water, ice, or snow on take-off, landing and manoeuvre surfaces.
• Wind Velocity; near the ground, the influence of wind on directional control and Cross Wind Landings or take-offs can, if not dealt with effectively, lead to Runway Excursion.
• Precipitation; for example rain, hail, and snow affect aerodynamics and visibility.
• Lightning; a lightning strike can be very distressing to passengers (and crew!) but physical damage to an aircraft only very rarely threaten the safety of an aircraft. Of greater concern is the effect a lightning strike can have on avionics, particularly compass and air data systems, and in case of rear mounted jet engines, the potential for the transient airflow disturbance associated with lightning to cause engine shutdown on both Full Authority Digital Engine Control (FADEC) and non-FADEC engines because of their close spacing and exposure to the same airflow disturbance at the same time.

Many of the operational safety issues that are addressed within SKYbrary can be affected by weather:

• Runway Excursion: The indirect contribution of weather to runway surface state and the direct effect of crosswind component on directional control.
• Controlled Flight Into Terrain (CFIT): CFIT accidents often occur when an aircraft is in cloud or in reduced forward visibility, when the crew may be subject to extra workload, be distracted, or have reduced situational awareness associated with the weather conditions.
• Loss of Control: Commonly as a direct or indirect result of turbulence or windshear such as might be experienced in an unintentional excursion into active Cumulonimbus (Cb) clouds, or an encounter with a Microburst or because of exposure to In-Flight Icing which exceeds the capacity of the available or selected Aircraft Ice Protection Systems.

There are numerous specific mitigation strategies to maintain the safety of flight in certain types of weather. These may be technical, procedural, or navigation based, or all three, and it may be appropriate to re-route, delay or cancel a flight if no satisfactory mitigation is available. A common requirement is that all those associated with the safety of flight should have an understanding of meteorology appropriate to their operational role.

Organisation of Weather Knowledge on SKYbrary

The growing number of weather and environmental related articles on SKYbrary are organised into the following subject areas:

• In-Flight Icing
• Turbulence
• Volcanic Ash
• Weather Risk Management
• Weather Phenomena
• Cloud Formation
• Climatic Phenomena
• Atmosphere

Further Reading

• The theme of Hindsight 7 (EUROCONTROL's Safety Magazine) was Weather and contains a number of articles discussing hazards to aviation associated with weather phenomena.
• see also FAA "Lessons Learned from Transport Airplane Accidents": Inclement Weather / Icing