Pressurization system
The CJ4 has a fully automatic cabin pressurisation system. Cruise level, departure and landing elevation are determined from the FMS flight-plan entries made by the pilot. The rate and differential scheduling for flight is then computed automatically. Landing elevation may be entered manually. There is no manual ‘rate’ or pressure differential controller. Non-automatic or ‘standby’ control of cabin pressure relies on the cabin altitude limiter (max 14,800’) and the maximum differential pressure relief valve (max 9 psi). This abnormal operation requires the cabin to be de-pressurised by the pilot opening the ‘Cabin Dump’ valve before landing.
A high altitude mode will automatically schedule a lower cabin pressure (higher cabin altitude) for landing at airports above 8000’ elevation.
To avoid pressure bumping on take-off, once the power levers are set to take-off power, the pressurisation system will begin to pressurise the cabin very slightly (‘down’ to approx. -200’) during the take-off roll. For this, and other reasons, reduced power take-offs are not authorised in the CJ4.