The Weibull probability distribution can be used as an alternative model for task time estimates in the PERT estimating methodology. It has the same advantages as the traditional beta distribution for this application. It has additional benefits, however, that make it a preferred option.
McCombs, Edward L.; Elam, Matthew E.; and Pratt, David B.
"Estimating Task Duration in PERT using the Weibull Probability Distribution,"
Journal of Modern Applied Statistical Methods: Vol. 8
, Article 26.
Available at: http://digitalcommons.wayne.edu/jmasm/vol8/iss1/26