Why are aeroplanes not affected by lightning?

Clouds are made of water droplets and dust in the atmosphere at altitudes of 1 to 16 km.While traveling through air,due to friction,the water droplets get electrically charged.Lightning occurs due to sparking between oppositely charged clouds-a high voltage spark rushes towards the ground(at zero potential) through moisture-filled air.

If any ground based structure is on the path of the spark,the top of that structure is excited to a high electrical potential while its bottom (in contact with the ground) remains at zero potential.This high potentail difference sets a very high current in the structure causing sudden heat generation in the material and destruction.But in flying aeroplanes,there is nothing like a ground point which remains always at zero voltage.

Hence even if hit by a lightning,the plane's entire surface acquires the same high potential and due to lack of potential difference there is no current and hence no destruction.