When items are deleted from Flight Log they are simply hidden from view. Because of this you may recover an item if it was accidentally deleted. The "Recover Deleted Items" dialog is shown below:
First select the type of item you are trying to recover. Once you select the item type a list of all deleted items of that type are shown in the list to the right as shown below:
Each item will have a check box beside them. Check the box for each item you want to recover (in this case "Change Glow Plug").
Press the Recover to un-delete all selected items or press Cancel to exit.