21C Safety & Warning Devices

 

TTP	B1-L3	ATA 21C
Beech 90 Series	B2-L3	Safety and Warning Devices

Outflow and Safety Valves

 

The outflow and safety valves are mounted in the bulkhead at the rear of the cabin. The valves are the same but are plumbed with different hardware  to  establish  their  function. Both valves incorporate a negative pressure relief diaphragm with cabin pressure on one side and atmospheric pressure on the other. If atmospheric pressure exceeds cabin pressure, the diaphragm opens the valve to relieve cabin negative pressure. Both valves are also equipped with a maximum differential diaphragm and valve assembly, preset at 5.0 psid, that will prevent the cabin from overpressurizing.

 The outflow valve automatically meters the outflow of cabin air during pressurized operation in response to vacuum control forces from the controller.

 A drain valve in the line connecting the outflow valve to the controller is located on the side of the fuselage behind an access panel aft of the right- hand seat track.

 The safety valve, mounted just inboard of the outflow valve, contains a preset maximum differential relief valve to assure the cabin pressure does not exceed the prescribed 5.0 psi differential. The safety valve is connected to a vacuum line con- trolled by a dump solenoid valve. The solenoid valve is opened, and the safety valve is vacuum opened whenever the cabin PRESSURE– DUMP switch is placed in the DUMP position, or the compressed landing gear strut closes the landing gear safety switch.

CONTROLS AND INDICATIONS 

Cabin ALT HI/ALT WARNING

If the cabin pressure altitude reaches a value of 10,000 feet for aircraft through LJ-1352, and LW-1 and after, a baro-pressure switch on the back side of the overhead light control panel closes. This illuminates the ALT WARN annunciator.

 

For LJ-1353 and after, and LA-2 and after, an annunciator illuminates when the cabin altitude exceeds 12,500 feet.  On the C-90, the annunciation reads  CABIN ALT HI, while on the F-90, it reads ALT WARN. This warns the pilot of operation requiring the use of supplemental oxygen

 

DIAGNOSTICS 

Manometer Test Ports

Two test ports, located below the copilot circuit-breaker panel, are attached to a venturi in the P3 line running forward from the flapper valve. These test ports can be used to determine  the amount of air coming from the flow control units. When a water manometer is connected to the test ports, the differential pressure across the venturi shows the flow rate of the air. 

Cabin Altimeter and Pressure Differential Gauge

 

CABIN  ALTIMETER—Located  on  the  right side of the panel above the power quadrant and is coaxially located with the cabin pressure dif- ferential  gauge. It continuously indicates the actual cabin pressure altitude.

 CABIN PRESSURE DIFFERENTIAL GAUGE—Coaxially located with the cabin altimeter. It indicates the pressure differential between the cabin pressure and the outside atmospheric pressure.

 

 Cabin Climb Indicator

 

The indicator is in the center of the panel above the power quadrant. It continuously indicates the rate of any changes of cabin pressure.

 RIGHT CB PANEL Environmental Section

 PRESSURIZATION ANNUNCIATOR LIGHT

 

A red warning or yellow caution annunciator on the glareshield illuminates if the cabin altitude goes too high. The annunciator light is part of the annunciator system and is not controlled by the pressurization control system. A baropressure switch, on the backside of the cockpit overhead panel, controls the light.

ALTITUDE WARN (through LJ 1352)—An amber caution light illuminates if the cabin altitude exceeds 10,000 feet.

 CABIN ALT  HI  (LJ  1353  and  after)—A  red warning light illuminates if the cabin altitude exceeds 12,500 feet. (The annunciator reads CABIN PRESS LOSS on English CAA-certifi- cated aircraft.)

PTP  Beech 90 Series	B1	LOC		SGH
	B2	LOC		SGH