Due date expressions

A due date expression specifies due dates that are not standard (for example, not every n days, weeks, months, or years). For example, you might have an aircraft engine that requires a maintenance check on the last day of each month.

You enter due date expressions on the Frequency tab of the Preventive Maintenance (CM) application. Use the standard three-letter abbreviation for months. Days of the month do not require a leading zero (for example, 1 or 2 is valid).

The due date expression uses the following valid syntax:
  1. Valid parameters
    • Day
    • Week
    • Month
    • Year
    • Firstdayofmonth
    • Lastdayofmonth
    • Hour
    • Noon
    • Midnight
    • Every/
    • Weekday/
  2. Valid expressions
    • =
    • <>
    • >=
    • <=
    • And
    • Or
  3. Suffix for more directives
    • Colon (:)

Examples of due PMs

You can combine these parameters to define the next due date of a preventive maintenance (PM) record, as shown in the following examples.

Table 1. Example due date expressions for PMs
Scenario Due date expression
PM is due on the last day of every other month: due: month = every/2 and day = lastdayofmonth
PM is due before midnight on the third Monday of every month. However, if the year is 2005, the PM is due on 1 June. due: a or b
a: weekday = monday/3 and hour = midnight
b: year = 2005 and month = Jun and day = 1