Section 7
Description of the Airplane and Systems
Columbia 400 (LC41-550FG)
RC050002
Initial Issue of Manual: November 10, 2004
7-58
Latest Revision Level/Date: -/11-10-2004
Essential Bus
– The essential bus is diode fed from either the right or the left bus and provides
power for the Attitude Horizon, remote-mounted Turn Coordinator, Panel Lights, Annunciators,
Left Bus Relays, Fuel Pump, Stall Warning, Flaps, and the Right Bus Relays. Most of these
devices are individually protected with circuit breakers rated as follows: Attitude Horizon (3
amp), Turn Coordinator (3 amp), Panel Lights (7.5 amp), Annunciators (3 amp), Left Bus Relays
(5 amp), Fuel Pump (10 amp), Stall Warning (5 amp), Flaps (10 amp), and the Right Bus Relays
(5 amp).
Battery Bus
– Four items are connected to the so-called battery bus. These items are directly
wired to the battery, but the term battery bus is used for consistency. These items will operate
even if the left and right buses are turned off since they are directly connected to the right or left
battery. The items directly wired to the right battery include the Nav/Com Bypass Switch, Hobbs
Meter, and ELT. The courtesy lights/flip lights are directly wired to the left battery. A 3-amp
fuse protects each component and is not accessible from the cockpit.
Master Switches
– The system’s two master switches are located in the master switch panel to
the left of the rocker switch panel. This manual refers to each of the left and right split-rocker
switches as a master switch (left master switch and right master switch). Although these switches
are not technically “master” switches, as they do not control the entire system, it is a common
term used to prevent confusion. Each switch is a split-rocker design with the alternator switch on
the left side and the battery switch on the right side. Pressing the top of the alternator portion of
the split-switch turns on both switches, and pressing the bottom of the battery portion of the
split-switch turns off both switches. The battery side of the switch is used on the ground for
checking electrical devices and will limit battery drain since power is not required for alternator
excitation. The alternator switches are used individually (with the battery on) to recycle the
system and are turned off during load shedding. See the discussion on page 3-29.
Crosstie Switch
– The crosstie switch is the white switch located between the left and right
master switches. This switch is to remain in the OFF position during normal operations. The
crosstie switch is only closed, or turned on, when the aircraft is connected to ground power or in
the event of an alternator failure. This switch will join the left and right buses together for
ground operations when connected to ground power. In the event of a left or right alternator
failure, this switch will join the two buses allowing the functioning alternator to carry the load on
both buses and charge both batteries. If the crosstie switch is turned on during normal operations,
the system will operate normally, however, the two main buses will not be isolated and they will
function as a single bus.
Avionics Master Switch
–
The avionics master switch is located in the master switch panel to
the right of the ignition switch. The switch is a rocker-type design and connects the avionics
distribution bus to the primary distribution bus when the switch is turned on. The purpose of the
switch is primarily for protection of delicate avionics equipment when the engine is started.
When the switch is turned off, no power is supplied to the avionics distribution bus.