I'm trying to gather some information on fleet replacement of quints that run as first due engines as opposed to quints that run as dedicated "ladder" companies.

Generally, is it cost effective to run a quint as a first due engine? Are we wearing out a $600K apparatus as opposed to a $350K one?

Are these quints replaced on the same schedule? Is this figured by years (example: 7 years front line, 10 reserve) or by hours/mileage?

What's your schedule/criteria for engines, quints and ladders?