PDPIC stands for "Performing the Duties of Pilot in Command." It can be logged when an instructor is on-board the aircraft with the student but the student is performing all of the duties of the Pilot In Command.
PDPIC time can be used in lieu of the solo aeronautical experience requirements for the Commercial Certificate (FAR 61.129(a)(4) >).
In other words, the following flights from the Commercial Pilot Flight Syllabus can either be accomplished as Solo Flights (no instructor on board) or as PDPIC flights:
Stage 2 - Day 1
Stage 2 - Day 2
Stage 3 - Day 1*
Stage 3 - Day 2*
*Stage 3 - Day 1 and Stage 3 - Day 2 flights do not necessarily need to be completed Solo or PDPIC if the student already has 10 total hours of Commercial Solo or PDPIC. However, if the student does not have 10 hours of Solo or PDPIC time when adding Stage 2 - Day 1 and Stage 2 - Day 2 flights together then they will need to get to that minimum of 10 hours somehow. That is why it is also included in the first 2 flights of Stage 3.
Common Questions Regarding PDPIC Time:
Q: Does PDPIC count as Solo Flight Time?
A: No. Because there is an instructor on board, the pilot is not "Solo."
Q: Does the student log PDPIC time as PIC time in their logbook?
A: Yes.
Q: Can the instructor log PIC time when the student is performing PDPIC?
A: Yes.
Q: Can a student combine PDPIC and Solo Time to meet the Commercial Certificate requirements of FAR 61.129(a)(4)?
A: No. All 10 hours must be PDPIC OR Solo Time. It cannot be half and half or any other combination thereof.