Balanced Matrix / Project Manager vs. Functional Manager

Hi Cyber PMPs

While studyng for my PMP I have encountered a gray area. situation: In a Balanced Matrix Organization - The Project Manger requires a technical expert, but the Functional Manager does not want to release him/her. What is the PM's best course of action and where does true power rest?

Any help apprieciated, please and thanks   

** What is the best course of action? **

I believe this is really a PLANNING question in disguise, but others might conclude EXECUTING. I would answer differently for each.

PLANNING CASE -- The PM is most likely in "Activity Resource
Estimating" as a part of Time Management, since that's where we begin
to get specific with our activity-resource allocation requirements.

Now, the best thing to do as a part of PLANNING: "Identify an alternative resource and factor in implications on cost, risk, scheduling, procurement, and any other relevant component plans."

EXECUTING CASE -- Some might argue that this could happen as late as "Acquire Project Team" in EXECUTING, which means the FM is breaking his agreement as per the stakeholder approved PM Plan (which includes the blessings of sponsor & senior mgmt.) Best course of action: "Determine the impact of the lost resource on the project, and take your case to sponsor/senior mgmt."

** Where does true power rest? **

In PLANNING, with the FM. In EXECUTION, with the Sponsor/Sr. Mgmt. because the FM is violating the express agreement of the PM Plan.

I would be interested in others' viewpoints.

Complete explanation, thanks so much!

The grey area should be studied and cleared. It is supposed to be the thing that needs to be studied a lot. - Marla Ahlgrimm