Hazards and hazardous conditions in flight

During flight, the pilot can see and avoid many hazardous weather phenomena. By circumnavigating hurricanes, thunderstorms and areas of forecast severe turbulence, the flight should proceed smoothly. Fortunately the cruising altitudes of modern jet aircraft place the aircraft above the level of many weather conditions for the cruise portion of the flight. However, there is one meteorological hazard known as clear air turbulence (CAT) that occurs at cruise altitude and which is very difficult to detect. CAT can cause sudden and severe turbulence. It is often encountered in area where is jet-stream activity. Flight crewmembers should keep their seat harnesses on at all times. Passengers are also advised to keep seatbelts on when seated. The people on board most likely to have a serious injury from CAT are the cabin crew, who remain unrestrained during most of the flight.

Lightning strikes can occur as a result of heaving to fly in areas where cumulonimbus clouds are present. Damage to the airframe, instruments, radio communications and even the pilot’s vision can occur. Again, circumnavigating thunderstorm areas is the best way of avoiding this hazard.

Airframe and engine icing are potential in-flight dangers. When the aircraft flies through super-cooled rain, sleet or snow, ice may form. Clear airframe icing is difficult to detect. Super-cooled water droplets (with temperature as low as 40°C) freeze upon impact with the aircraft and if this continues, layers of ice build up. Ice may form on any part of the aircraft, including the compressor blades. If this happens, ice may be ingested into the engine causing damage and possibly requiring engines to be shutdown. There are reports of layers of clear ice forming on aircraft up to 5 cm thick, and remaining undetected by flight crew. Even if an aircraft is equipped with a de-icing system, the melting ice can run back over the airframe and re-freeze on trailing edge surfaces, introducing another hazard.

With increasing pollution in the world’s largest cities, levels of smoke and haze (tiny particles that can be found suspended in the air, even at the highest altitudes) can greatly affect visibility and during flight, interfering with the engines. ’Slant visibility’ occur when a pilot’s ability to see through layers of haze is severely restricted. In this situation, while vertical visibility may remain acceptable, the pilot’s diagonal line of sight is significantly reduced. On approach or in the circuit, this phenomenon can be most apparent when the aircraft is preparing for landing. The particular combination of smoke and fog, know as smog, is becoming common in bigger cities, increasing the need for weather warnings in severe smog conditions. Ash emitted by active volcanoes in various locations around the world can also be extremely hazardous.

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