ALL large passenger aircraft have Outflow Valves.. Some even have 2!
Here is an excerpt from the A340-200 Maintenance Manual
21-30-00 PB 001 - PRESSURIZATION CONTROL - DESCRIPTION AND OPERATION
1. General
The pressurization control system controls the pressure in the fuselage. It operates fully automatically and has a manual backup. The pressure change rate is controlled to give satisfactory pressure values of safety and comfort for the passengers and crew.
2. System Description
The pressurization control system has the subsequent subsystem:
- pressure control and monitoring.
The pressure control and monitoring system (Ref. 21-31-00) makes sure that the pressure in the fuselage is safe and comfortable for the passengers and crew. Cabin pressure controllers control the quantity of air that flows out of the fuselage through two outflow valves. Two safety valves and a negative-pressure relief valve are installed for safety.
Hope this helps.
PLM
Edited because I'm a plank!
Last edited by PondLifeMan; 13th Dec 2005 at 17:25.