Logging PIC

Al German concisely explains this issue reprinted here from faa.gov:

Proper logging of PIC time is a favorite subject of CFI’s sitting around these rainy  days. And that’s not unusual since in the FAA’s own words in the Federal Register  "The FAA acknowledges there has been confusion in the past regarding the  logging of pilot-in-command time by these pilots and that inconsistent policy opinions  have been issued by the FAA". In researching the subject FAR Parts 61 & 91, the Federal Register comments issued during the major revision to Part 61 in August 1997, "Federal Aviation Regulations Explained" published by Jeppesen, and various other aviation monthly publications were reviewed.

First lets be clear: who is, or can be, pilot-in-command (PIC) and who may log PIC time are two separate issues and are only sometimes related. FAR Part 1 defines the pilot-in-command as follows: "Pilot-in-command means the person who:
1. Has the final authority and responsibility for the operation and safety of the flight;
2. Has been designated as pilot-in-command before or during the flight; and
3. Holds the appropriate category, class, and type rating, if appropriate, for the conduct of the flight."

Part 91.3 expands those comments making it clear that anything that happens during the flight is the sole responsibility of the pilot-in-command.  According to the Federal Register there are only three ways a private or commercial pilot can properly log pilot-in-command time.

1. When the pilot is the sole manipulator of the controls of an aircraft for which the pilot is rated.
2. When the pilot is sole occupant of  the aircraft.
3. When the pilot is acting as pilot-in-command of an aircraft for which  more than one pilot is required  under the regulations under which  the flight is conducted.

Far Part 61.51 "Pilot Logbooks" covers the  logging of pilot time and section (e)  addresses logging PIC time.  A private or commercial pilot may log PIC  time if that person is "the sole manipulator  of the controls of an aircraft for which the  pilot is rated" [61.51 (e)(1)(i)]
Thus a non-instrument rated pilot taking  instrument flight instruction, if rated in the  aircraft, may log PIC based on the "sole  manipulator of the controls" rule. Since  there is nothing in the rules that  addresses meteorological conditions, the  pilot may log PIC while in the clouds. This  is supported by FAA chief counsel  opinions [Federal Regulations Explained-Jeppesen].

A private or commercial pilot may log PIC  time when "acting as pilot-in-command of  an aircraft on which more than one pilot is  required under the - - - - regulations under  which the flight is conducted". [61.51  (e)(1)(ii)]  Normally, a safety pilot, required by  regulations, who scans for traffic for a pilot  flying under simulated instrument  conditions is not pilot-in-command and  thus logs second-in-command. However,  if the two pilots agree that the safety pilot  is designated pilot-in-command, the safety  pilot/pilot-in-command may log PIC since  he is the pilot responsible for the  operation and safety of the aircraft. The  pilot flying is "sole manipulator of the  controls for which the pilot is rated"" and  may also log PIC. Therefore, two private  pilots may log PIC under these conditions.  However, the safety pilot/pilot-in-command must realize that anything that  occurs during the flight is his  responsibility. Airspace violations, non- compliance with ATC instructions, near  mid air collision, and runway incursions on  the ground are all now charged to the  safety pilot.

A recent article in a monthly  aviation publications discussed a flight  where there was a violation and the two  pilots disagreed who was pilot-in-command.  However, two pilots may not simultaneously log PIC when one pilot is sole manipulator of the controls and the  other is acting as pilot-in-command if the  regulations governing the flight do not  require more than one pilot.  "An airline transport pilot may log as PIC  time all of the flight time while acting as  pilot-in-command of an operation requiring  an airline transport certificate." [61.51  (e)(2)] Previous regulations allowed a  situation where three pilot (one an ATP)  could log PIC simultaneously when  conducting an operation which did not require an airline transport pilot. This is no  longer allowed under the August 1997 revision.

A flight instructor may log PIC "while  acting as a authorized instructor". No  change to previous regulations.  A student pilot can now log PIC. That’s  new, and since there is no restriction, your  logbook can be updated so that all student  solo time prior to August 4, 1997 may be  logged as PIC. When an instructor is  aboard, since the student is not rated in
the aircraft, flight instruction is still logged  as dual not PIC.  Then there are some unusual situations  which occur. A private pilot flying with his  friend (a CFI or ATP) aboard as a passenger. What is the status of the CFI  or ATP who is obviously a more senior  pilot with more experience than the private  pilot? The regulations don’t address this  situation, but the courts may find that the  more senior pilot has some or all the  responsibility for the operation or safety of  the flight.

In summary, the person who is pilot-in- command may log PIC, others may also log PIC depending in the circumstances.