Triple Asterisks (***) definition
Triple Asterisks (***) means that the item is either optional or is not required to be installed on all aircraft covered by the MMEL. This item may be included on the operator's MEL after the approving office has determined that the item has been installed on one or more of the operator's aircraft. The symbol, however, shall not be carried forward into the operator's MEL. It should be noted that neither this policy nor the use of this symbol provides authority to install or remove an item from an aircraft. The "***" symbol may be considered equivalent to the term "if installed"