14 CFR § 135.159

A gyroscopic rate-of-turn indicator except on the following aircraft:

Airplanes with a third attitude instrument system usable through flight attitudes of 360 degrees of pitch-and-roll and installed in accordance with the instrument requirements prescribed in § 121.305(j) of this chapter.

Helicopters with a third attitude instrument system usable through flight attitudes of ±80 degrees of pitch and ±120 degrees of roll and installed in accordance with § 29.1303(g) of this chapter.

Helicopters with a maximum certificated takeoff weight of 6,000 pounds or less.

A slip skid indicator.

A gyroscopic bank-and-pitch indicator.

A gyroscopic direction indicator.

A generator or generators able to supply all probable combinations of continuous in-flight electrical loads for required equipment and for recharging the battery.

For night flights—

An anticollision light system;

Instrument lights to make all instruments, switches, and gauges easily readable, the direct rays of which are shielded from the pilots' eyes; and

A flashlight having at least two size “D” cells or equivalent.

For the purpose of paragraph (e) of this section, a continuous in-flight electrical load includes one that draws current continuously during flight, such as radio equipment and electrically driven instruments and lights, but does not include occasional intermittent loads.

Notwithstanding provisions of paragraphs (b), (c), and (d), helicopters having a maximum certificated takeoff weight of 6,000 pounds or less may be operated until January 6, 1988, under visual flight rules at night without a slip skid indicator, a gyroscopic bank-and-pitch indicator, or a gyroscopic direction indicator.