Apparatus and method for extending a fly section of a telescopic crane boom which fly section does not have its own power extension/retraction unit. The crane boom comprises at least a first or fly section, a second section, and a third or base section. Linearly extendable power screws are located within the boom for extending the second section from the base section, being connected between the base section and the second section to effect movement of the latter. To set up the crane for operation, the power screws extend the second section from the base section, a load pin connecting the fly section and the second section is released, and a pair of stop pins engages the fly section in its sides. The stop pins prevent movement of the fly section relative to the base section. Thus, when the second section is thereafter retracted into the base section, the fly section is left extended from the second section. A hole at the inside of the fly section and the load pin are at this point in alignment and the load pin may be inserted to engage both sections. The power screws are now in readiness to independently operate the second section, with the fly section fully extended on the second section.