FLOAT PATHS

There are several reasons why you can observe discontinuous float paths, most notably resource leveling, portions invisible to software that cannot create resource dependencies.

If you are using resource leveling this can be a suspect, but not necessarily guilty.

Use of multiple calendars can create paths with different float values among a common chain.

Modeling of real life just makes it harder, not unnecessarily wrong, on the other hand not using these functionalities when needed can yield wrong models. If you do not have enough resources then not considering these constraints will yield impossible schedules, same as if you do not make use of the appropriate calendars.

Keep in mind that Longest Path is not necessarily the Critical Path, your major concern should be the chain that composes the critical path, either to the job in general or to contractual milestones.

After a few thoughts about float paths not making much sense I would like to add other comments about the analysis of multiple paths.

http://www.cassellconsulting.com/consulting/multiple-float-paths-in-p6.html

http://ronwinterconsulting.com/Longest_Path_Value.pdf

In theory simple computation but short if missing the statistical element.

I would not trust an algorithm that order multiple paths based on an arbitrary measure that does not take into account the probabilities of each path be delayed and by how much, too much is missing.

Google for Criticality Index and you will find even this metrics is limited and alone can be misleading.

Here the scientific approach would be using Statistical Modeling within your CPM software, it can be via Monte Carlo or or other Statistical modeling. Beware that the application of Monte Carlo using external software might invalid the analysis. This will provide you with the tools to measure the probabilities of success as you change your strategies.

I would like to highlight Ron Winter argument about how out of sequence activities makes it difficult to trace the critical path, a very interesting article you should read. If you software is capable of filtering for active driving links then the identification of completed out of sequence activities in the critical path shall be no problem. Do your homework and remove all out of sequence occurrences, even on activities completed, this will eliminate the need for esoteric procedures. In any case it is not always by working on the critical path that you increase your success probabilities.

Float is not real, useful metrics but in no way absolute.