In a software development firm that I work for, contracts are billed based on 3 items: Design, Development, and PM.
Example: A simple software project could take 200 hours and would be broken down into the following hours: 90/90/20 (Design/Development/PM)
I can imagine the profitability of the project being affected if Design and Development exceed the allocated 90 hours each. However, should it be a concern if the PM time exceeds the 20 hour mark? I mean, is the PM even considered a billable resource?
Traditionally, the companies I used to work with practice the philosophy that a PM must spend as many hours as it takes to make the project successful.
But how is this viewed from a PMBOK/Prince 2 methodology? Please note that I am not asking for a personal opinion or a poll. I would like a response that is based on some formal methodology (if possible as I'd like to make this as objective as possible).
I found a very similar question here: Should a PM also be a resource on the project? Why? From the answers there, I liked Mark Phillips' answer the best (being a 'no') as impartiality is required from the PM's perspective. However, I don't feel that that question is as specific as mine as it doesn't address the billable aspect.