Airborne weather radar is a type of radar used to provide an indication to pilots of the intensity of convective weather. Modern weather radars are mostly doppler radars, capable of detecting the motion of rain droplets in addition to intensity of the precipitation.
Typically, the radar antenna is located in the nose of the aircraft. Signals from the antenna are processed by a computer and presented on a screen which may be viewed by the pilots. Droplet size is a good indicator of strong updrafts within cumulonimbus clouds, and associated turbulence, and is indicated on the screen by patterns, colour coded for intensity.
Some airborne weather radar systems may also be able to predict the presence of wind shear.
EU-OPS 1.670 requires that:
(a) An operator shall not operate:
(1) A pressurised aeroplane; or
(2) An unpressurised aeroplane which has a maximum certificated take-off mass of more than 5 700 kg; or
(3) An unpressurised aeroplane having a maximum approved passenger seating configuration of more than 9 seats after 1 April 1999,
unless it is equipped with airborne weather radar equipment whenever such an aeroplane is being operated at night or in instrument meteorological conditions in areas where thunderstorms or other potentially hazardous weather conditions, regarded as detectable with airborne weather radar, may be expected to exist along the route.
(b) For propeller driven pressurised aeroplanes having a maximum certificated take-off mass not exceeding 5 700 kg with a maximum approved passenger seating configuration not exceeding 9 seats the airborne weather radar equipment may be replaced by other equipment capable of detecting thunderstorms and other potentially hazardous weather conditions, regarded as detectable with airborne weather radar equipment, subject to approval by the Authority.