dry cranking and wet cranking ?
 

i know what they are but i dont know why do we use them ?

Dry cranking,wet cranking.
 

Dry cranking (or dry cycling) would be a requirement if you had changed a starter motor or tacho generator. Wet cranking (or wet cycling) would be a requirement after FCU/MEC change in order to purge and bleed the fuel system. Note:- After a wet cycle remember to carry out a dry cycle prior to any engine runor you may be awarded the "Flame of the month award"

Dry motoring can also be done if you wish to get an engine's accurate engine oil level if the aircraft has been on the ground for a long time.

LOL !:) Actually, you can skip the dry cycle if you wish to have an impromptu barbecue party. :)

thanks i understand now :D