Aircraft Systems: Pre-Flight Setup and APU Activation

Study Notes

Pre-Flight Setup and Pack Activation

APU must be running for air conditioning.
Cockpit overhead panel push buttons are set to "lights out," except pack "off" lights.
Turning a pack push button "on" triggers an amber fault light if no bleed air is available. This is normal until the APU bleed air connects.
Pack Flow Selector is set to "Normal" for standard passenger loads. Flow rates modify only after engine bleed air is available.

Connecting APU Bleed to Packs

Activating the APU bleed push button connects the APU to the packs.
APU Valve displays a green in-line indication.
Crossbleed Valve opens automatically.
Fault lights extinguish, pack flow valves open, and pack flow increases as bleed air is supplied.
Conditioned air is distributed through the mixing unit.

Temperature Regulation

Zone temperature control uses trim air valves to add warm bleed air to pack-conditioned air.
For example, If the cockpit zone temperature is set for 24°C, but the duct temperature is 15°C, the trim air valve opens and warms air until the desired temperature is achieved.
Trim air valves dynamically regulate temperature.
Temperature range on the zone selector is from 18°C (cold) to 30°C (hot). Each increment on the selector represents a 2°C change.

Engine Start and Bleed Priority

When the engine mode selector is set to "ignition/start," pack valves close to direct all APU bleed air toward engine starting.
If the engine master switch is not activated within 30 seconds, the pack valves briefly reopen.
After engine start, pack valves reopen allowing APU bleed air to the packs again.
Engine bleed air takes over by switching off the APU bleed push button. Engine bleed valves open, and the APU bleed valve closes.
During takeoff from performance-limited runways, packs can utilize APU bleed to maintain engine performance.

In-Flight and Post-Landing Operations

Air conditioning functions automatically; pilots adjust zone temperatures.
Pack Flow Selector can be set to "Low" to conserve fuel during low passenger loads, or "High" for hot conditions or full loads to ensure sufficient cooling (increasing engine bleed demand and fuel usage).
After engine shutdown, the system can operate on APU bleed or use an external conditioning unit (no cockpit indication for using the external unit).

Key Notes

The air conditioning system is largely automated, with minimal pilot intervention required for flow and temperature regulation.
Lower pack flow settings save fuel during low-demand conditions.
An external conditioning unit provides cooling without requiring cockpit controls or indications.

Description

Test your knowledge on the pre-flight setup and APU activation processes in aircraft systems. This quiz covers essential procedures such as cockpit configurations, APU bleed connections, and temperature regulation. Ensure you're familiar with standard practices for optimal passenger comfort and safety.