14 CFR § 437.59 - Key flight-safety event limitations.
(a) A permittee must conduct any key flight-safety event so that the reusable suborbital rocket's instantaneous impact point, including its expected dispersion, is over an unpopulated or sparsely populated area. At a minimum, a key flight-safety event includes:
(1) Ignition of any primary rocket engine,
(2) Any staging event, or
(3) Any envelope expansion.
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