A method to reduce the rejection rate for low performance at the acceptance test of PWC PT6T-6 overhauled power sections

Alfa Romeo Avio is involved in the overhaul process of the Pratt & Whitney of Canada PT6T-6 for the helicopter fleet of the Italian Army and civil services. The overhauled power sections suffered from a high rejection rate (about 40 percent) for low performance at the acceptance test. Alfa Romeo Avio R&D investigated the causes and developed a method to reduce the rejection rate. A first contribution to the decision support method for the selection of the optimal engine configuration can be obtained from engine thermodynamic cycle simulation, which gives indications on the behavior of the average overhauled power section. In this paper the authors also describe a statistical model based on a cause/effect correlation between power section assembly variables and performance parameters. A simulation procedure, based on the statistical model, estimates the influence of the configuration assembly data on the power section performance parameters. A careful application of both statistical and thermodynamic models gives predictions on the optimum matching of turbine nozzle size to reach the target performance at the engine acceptance test. The method has been tested on the field during the last two years and a reduction in the rejection rate at the acceptance test to 18 percent has been obtained.