14 CFR § 135.99

No certificate holder may operate an aircraft with less than the minimum flight crew specified in the aircraft operating limitations or the Aircraft Flight Manual for that aircraft and required by this part for the kind of operation being conducted.

No certificate holder may operate an aircraft without a second in command if that aircraft has a passenger seating configuration, excluding any pilot seat, of ten seats or more.

Except as provided in paragraph (d) of this section, a certificate holder authorized to conduct operations under instrument flight rules may receive authorization from the Administrator through its operations specifications to establish a second-in-command professional development program. As part of that program, a pilot employed by the certificate holder may log time as second in command in operations conducted under this part and part 91 of this chapter that do not require a second pilot by type certification of the aircraft or the regulation under which the flight is being conducted, provided the flight operation is conducted in accordance with the certificate holder's operations specifications for second-in-command professional development program; and—

The certificate holder:

Maintains records for each assigned second in command consistent with the requirements in § 135.63;

Provides a copy of the records required by § 135.63(a)(4)(vi) and (x) to the assigned second in command upon request and within a reasonable time; and

Establishes and maintains a data collection and analysis process that will enable the certificate holder and the FAA to determine whether the second-in-command professional development program is accomplishing its objectives.

The aircraft is a multiengine airplane or a single-engine turbine-powered airplane. The aircraft must have an independent set of controls for a second pilot flightcrew member, which may not include a throwover control wheel. The aircraft must also have the following equipment and independent instrumentation for a second pilot:

An airspeed indicator;

Sensitive altimeter adjustable for barometric pressure;

Gyroscopic bank and pitch indicator;

Gyroscopic rate-of-turn indicator combined with an integral slip-skid indicator;

Gyroscopic direction indicator;

For IFR operations, a vertical speed indicator;

For IFR operations, course guidance for en route navigation and instrument approaches; and

A microphone, transmit switch, and headphone or speaker.

The pilot assigned to serve as second in command satisfies the following requirements:

The second in command qualifications in § 135.245;

The flight time and duty period limitations and rest requirements in subpart F of this part;

The crewmember testing requirements for second in command in subpart G of this part; and

The crewmember training requirements for second in command in subpart H of this part.

The pilot assigned to serve as pilot in command satisfies the following requirements:

Has been fully qualified to serve as a pilot in command for the certificate holder for at least the previous 6 calendar months; and

Has completed mentoring training, including techniques for reinforcing the highest standards of technical performance, airmanship and professionalism within the preceding 36 calendar months.

The following certificate holders are not eligible to receive authorization for a second-in-command professional development program under paragraph (c) of this section:

A certificate holder that uses only one pilot in its operations; and

A certificate holder that has been approved to deviate from the requirements in § 135.21(a), § 135.341(a), or § 119.69(a) of this chapter.