Atmospheric Effects on Flight Review 1 ATC Chapter 7

Aim To review atmospheric effect on flight

Objectives State the correct procedure for taxiing in strong winds Define wind shear and state its effect on flight characteristics Define the different types of turbulence and state their effect on flight characteristics

1. Taxiing Taxiing Incorrect taxi technique in strong winds can lead to the aircraft becoming uncontrollable and in the worst case scenario flipping, spinning or skidding resulting in damage to the aircraft or passengers

1. Taxiing Taxiing When taxiing with a head wind the control column should be held backwards and into wind

Remember “Climb into, Dive away from” 1. Taxiing Taxiing When taxiing with a tailwind the control column should be held forwards and away from wind Remember “Climb into, Dive away from”

2. Wind Shear Wind Shear Wind shear is a rapid change in wind speed or direction The most dangerous phase of flight to encounter wind shear is during take-off or landing where the aircraft is low and slow Incorrect recovery technique results in a number of incidents and accidents every year, generally speaking increasing your approach or take-off speed and the use of reduced flap settings will minimise the effects of wind shear

3. Turbulence Mechanical Turbulence When flying in close proximity to the ground it is important to have some understanding of the way in which local winds will interact with ground features Upper level winds will often be different from the wind at low level. We need to keep an eye out for wind indications on the ground Wind speeds below around 15 KTS are generally smooth and predictable Wind speeds above 15 KTS are turbulent and harder to predict At wind speeds above 20 KTS severe wind shear and turbulence can occur. Continued flight in these conditions is not advisable, consider climbing or alternate tracking

3. Turbulence Updrafts and Downdrafts Once you have some idea of the wind velocity you should be able to predict how the air is flowing over ground features and adjust your performance accordingly before it affects the aircraft On the windward side of the obstacle we can expect an updraft. In order to counteract this we must: Lower the nose Decrease power On the lee side of the obstacle we can expect a downdraft. In order to counteract this we must: Raise the nose Increase power Strong updrafts and downdrafts are extremely hazardous. Vertical speeds of up to 3000ft/min can occur with strong winds. If in doubt do not continue the flight

3. Turbulence Thermals Thermals are rising currents of air caused by uneven heating of the ground They can result in very turbulent conditions and reach their peak around mid afternoon The formation of fair weather cumulus clouds are an indication of thermal activity

3. Turbulence Wake Turbulence As the wing produces lift trailing edge vortices are also produced, known as wake turbulence The larger the aircraft and the more lift being produced the larger the vortices If a light aircraft gets caught in the wake turbulence of a larger aircraft it can become uncontrollable

3. Turbulence Helicopter Downwash Helicopter blades produce downwash in order to produce lift, the larger, heavier or slower the helicopter, the more downwash produced Downwash can be hazardous up to a radius three times the diameter of the rotor

Questions?