((a)) ** In general** The taxes imposed by sections 4261 and 4271 shall not apply to transportation by an aircraft having a maximum certificated takeoff weight of 6,000 pounds or less, except when such aircraft is operated on an established line or when such aircraft is a jet aircraft.

((b)) ** Maximum certificated takeoff weight** For purposes of this section, the term “maximum certificated takeoff weight” means the maximum such weight contained in the type certificate or airworthiness certificate.

((c)) ** Sightseeing** For purposes of this section, an aircraft shall not be considered as operated on an established line at any time during which such aircraft is being operated on a flight the sole purpose of which is sightseeing.

((d)) ** Jet aircraft** For purposes of this section, the term “jet aircraft” shall not include any aircraft which is a rotorcraft or propeller aircraft.