A "Build-up Line" is this...
First the hard lines are awarded. Then, any trips that fall out due to vacation, training days, leave of absence, military days, etc. are moved into the build-up lines.
If you bid a build-up you will also submit a "build-up preference" that is considered in order of seniority. For example: if you are the most senior pilot to be awarded a build-up and your preference is for all tue-wed-thu off and only two to three day trips, the scheduling system will figure out the best trips that give him what he wants and keep his block hours from 80 to 95 hours.
After his award then the next pilot to be awarded a build-up is then given their preference. The catch is that really only the first third to half get most of what they want. Sometimes more, sometimes less. It really depends on the month and many other factors.
Hope this helps and good luck to you all!
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"It takes a big man to cry. It takes a bigger man to laugh at that man".