14 CFR § 91.109

No person may operate a civil aircraft (except a manned free balloon) that is being used for flight instruction unless that aircraft has fully functioning dual controls. However, instrument flight instruction may be given in an airplane that is equipped with a single, functioning throwover control wheel that controls the elevator and ailerons, in place of fixed, dual controls, when—

The instructor has determined that the flight can be conducted safely; and

The person manipulating the controls has at least a private pilot certificate with appropriate category and class ratings.

An airplane equipped with a single, functioning throwover control wheel that controls the elevator and ailerons, in place of fixed, dual controls may be used for flight instruction to conduct a flight review required by § 61.56 of this chapter, or to obtain recent flight experience or an instrument proficiency check required by § 61.57 when—

The airplane is equipped with operable rudder pedals at both pilot stations;

The pilot manipulating the controls is qualified to serve and serves as pilot in command during the entire flight;

The instructor is current and qualified to serve as pilot in command of the airplane, meets the requirements of § 61.195(b), and has logged at least 25 hours of pilot-in-command flight time in the make and model of airplane; and

The pilot in command and the instructor have determined the flight can be conducted safely.

No person may operate a civil aircraft in simulated instrument flight unless—

The other control seat is occupied by a safety pilot who possesses at least:

A private pilot certificate with category and class ratings appropriate to the aircraft being flown; or

For purposes of providing training for a solo cross-country endorsement under § 61.93 of this chapter, a flight instructor certificate with an appropriate sport pilot rating and meets the requirements of § 61.412 of this chapter.

The safety pilot has adequate vision forward and to each side of the aircraft, or a competent observer in the aircraft adequately supplements the vision of the safety pilot; and

Except in the case of lighter-than-air aircraft, that aircraft is equipped with fully functioning dual controls. However, simulated instrument flight may be conducted in a single-engine airplane, equipped with a single, functioning, throwover control wheel, in place of fixed, dual controls of the elevator and ailerons, when—

The safety pilot has determined that the flight can be conducted safely; and

The person manipulating the controls has at least a private pilot certificate with appropriate category and class ratings.

No person may operate a civil aircraft that is being used for a flight test for an airline transport pilot certificate or a class or type rating on that certificate, or for a part 121 proficiency flight test, unless the pilot seated at the controls, other than the pilot being checked, is fully qualified to act as pilot in command of the aircraft.