The number and type of exits on an aircraft is regulated through strict rules within the industry, and is based on whether the aircraft is single or twin-aisled; the maximum passenger load; and the maximum distance from a seat to an exit. The goal of these regulations is to make possible the evacuation of an airliner's designed maximum occupancy of passengers and crew within 90 seconds even if half of the available exits are blocked. Any aircraft where the emergency exit door sill height is above that which would make unaided escape possible is fitted with an automatic inflatable evacuation slide, which allows occupants to slide to the ground safely. † 9 passenger aircraft only  Ventral exits must allow the same rate of egress as a Type I exit, tailcone exit are aft of the fuselage. Aircraft for less than 19 passenger must have one sufficient exit in each side of the fuselage, two per side for more, no more than apart from each other. In November 2019, the EASA allowed 'Type-A+' exits with a dual-lane evacuation slide to increase maximum accommodation increased to 480 seats up from 440 with four pairs of doors on the A350-1000, and up to 460 on the A330-900.