14 CFR § 31.19 - Performance: Uncontrolled descent.
(a) The following must be determined for the most critical uncontrolled descent that can result from any single failure of the heater assembly, fuel cell system, gas value system, or maneuvering vent system, or from any single tear in the balloon envelope between tear stoppers:
(1) The maximum vertical velocity attained.
(2) The altitude loss from the point of failure to the point at which maximum vertical velocity is attained.
(b) Procedures must be established for landing at the maximum vertical velocity determined in paragraph (a)(1) of this section and for arresting that descent rate in accordance with paragraph (a)(3) of this section.