The crew of large passenger jets use onboard weather radar to avoid any thunderstorms, so pilots of light aircraft should show equal respect for their destructive power!
In flight, you should stay at least 10nm away from a cumulonimbus, and preferably more than 20nm away.
Severe Turbulence Turbulence created in and around a cumulonimbus is so severe that proper control of a light aircraft can become almost impossible. This can lead to large, undesired changes in altitude & heading, as well as continuous buffeting. This exposes the airframe to heavy structural loads and can cause injury to occupants or aircraft damage.
Airframe Ice Thunderstorms contain very water droplets, both inside the cloud and falling from it as rain. Any time an aircraft is exposed to this where temperatures below 0°C exist, ice can be expected to form. A build-up of ice on the aircraft reduces performance and control, which only makes matters worse for a pilot who is already experiencing severe turbulence.
Hail Large hail can be encountered inside a thunderstorm or in the clear air underneath & beside it. Hail is usually only encountered for short periods of time but it can still cause severe airframe damage, with leading edges and windscreens sometimes being left battered with dents and holes.
Lightning Lightning is an electrical spark that flows through the air. If an aircraft is in the way, lightning will often flow through the aircraft. This can cause damage to aircraft electrical systems, render the magnetic compass useless and potentially start a fire if the lightning is forced to arc across parts of the airframe that are not well bonded.
Wind Shear A very sudden change of wind speed and direction at different heights can result in an instant loss of lift and airspeed, leading to an uncontrolled descent.
Microbursts Many thunderstorms have localised areas of very intense downdraughts, in addition to the main downdraught from the cell. These pockets of cold air, known as microbursts, can cause large changes in vertical and horizontal wind speeds. This has caused large airliners to crash in the past, so the dangers to us as light aircraft pilots should be obvious!
Tornadoes Tornadoes occur in very unstable atmospheres where there is intensive thunderstorm activity. They are funnel shaped clouds that touch the ground and can have wind speeds of 250 knots along their narrow path.
Waterspouts Two types of waterspouts exist – the first is essentially a small tornado over the ocean, where a cumulonimbus sucks water up through the centre of a funnel shaped cloud. The second is a very localised centre of low pressure, typically about 100ft in diameter with wind speeds of 30 to 50 knots. The low pressure lifts water up into the air to create a waterspout. They are usually short lived. Both types of waterspouts should be avoided by pilots.
At the private pilot level, you are generally expected to have an idea of the hazards associated with thunderstorms but not the intricacies of each. In other words, you should be able to recognise the above headings but not necessarily the details underneath each.
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