The general purpose of a Telcordia calculation method is to adjust a base failure rate by taking into account burn-in, laboratory, and/or field data. Definitions of the terms used by these methods appear in Calculation Method Terms.

When a calculation method that supports burn-in data is selected, the Telcordia Issue 1 model calculates the first year multiplier (Π FY) if burn-in data is entered. The Telcordia Issue 2 and Issue 3 models calculate the same value but refer to it as an early life factor (Π ELF). The value for Π FY or Π ELF is used to determine the predicted failure rate for the item over the first year.

Essentially, during the first year of an item’s life, the failure rate starts out high and then gradually decreases until the steady state failure rate is reached. This is referred to as the first year drop out. It is an indication of the failure rate during the infant mortality phase of the product life. For more information, see First Year Dropout Calculations.

Your choice of a particular calculation method depends upon analysis requirements and the amount of data available. While general descriptions of all calculation models appear in subsequent topics, you should see the Telcordia document, Reliability Prediction Procedure for Electronic Equipment, for detailed information.

If the calculation method that you select supports the use of burn-in, laboratory, and/or field data, fields for collecting this data become available in the Method Data pane for the assembly or for the part, depending on the level at which the data was collected. To use a calculation method with a MIL-HDBK-217, Telcordia, or Bellcore model, you select it for Method in the Calculation Data pane for the parent assembly. To use these methods with other supported models, you can temporarily switch the model selected in this pane to a MIL-HDBK-217, Telcordia, or Bellcore model so that Method is shown. After selecting a method, you can switch back to the original model.