From my personal experience, the first point of contact for you being the line manager, you need to communicate to him first.
I would follow the following procedure:
- Talk to your line manager and remind him about the project deadline.
- Inform your line manager that you will have to give a status update to your department head well before you update your department head. At that point you can say something like, "Boss this is the only item left, can you get it done before the 10 o'clock project status meeting?"
- Then, when your department head asks for the status, you can mention that the task is nearly done and the line manager will be looking into the remaining part of it.
Remember that what communication goes on between your line manager and department head is not your concern. If they have an understanding about the task being delayed, you will not be held responsible for it. And if there is no such communication between them, since you have already informed your line manager about the possible update you need to give to your department head, your line manager or even the department head cannot hold you responsible for the slip.
