One crew member per 50 seats (occupied or not) are usually required and what is always planned on. There's no requirement for one FA to guard one or more doors (no different to doors 2 or 3 on a 321).
It's a CAA approved procedure that under certain circumstances reduced cabin crew may be carried due to a crew member going sick 'down route' as it were down a maximum of 50 pax (not seats) per operating crew member. It is extremely rare and I've never seen it done 7 years.
Flights can not and are never planned to operate with less than minimum crew. However you cannot depart certain airports with reduced crew. What route was this on and at what time?
Last edited by HeartyMeatballs; 3rd Oct 2015 at 17:24.
Reason: Clarification