Section 28-405.3.2. Class B license

All applicants for a class B hoisting
  machine operator license shall hold a class  A  basic  hoisting  machine
  operator license, and shall have had at least two years experience prior
  to  application under the direct and continuing supervision of a Class B
  licensed hoisting machine operator operating  the  equipment  for  which
  they  are  applying for endorsement and shall satisfactorily demonstrate
  by operation that they are competent to operate a  crane  with  a  boom,
  including  jibs  and other extensions, exceeding 200 feet (60 960 mm) in
  length or truck-mounted tower crane exceeding 200  feet  (60 960 mm)  in
  height, or as otherwise provided in rules of the department.