(a) For the purpose of this chapter, it is lawful to temporarily render a safety device incapable of proper or effective action or to materially impair its function if this action is taken as provided for in paragraph (b) or (c) of this section.

(b) If a locomotive is equipped with a device to assure that the operator is alert or not physically incapacitated, that device may be deactivated when:

(1) The locomotive is not the controlling locomotive;

(2) The locomotive is performing switching operations and not hauling cars in a manner that constitutes a train movement under part 232 of this chapter:

(3) The locomotive is dead-in-tow; or

(4) The locomotive is a mid-train slave unit being controlled by radio from a remote location.

(c) If a locomotive in commuter or intercity passenger service is equipped with a device to record data concerning the operation of that locomotive or the train it is powering, that device may be deactivated only under the provisions of § 229.135 of this chapter. Inward- and outward-facing image recording devices on commuter or intercity passenger locomotives may be deactivated only under the provisions of § 229.136 of this chapter. This section does not apply to inward- or outward-facing image recording devices that are installed on freight locomotives.