Air System Flashcards
How many packs?
3
How many temperature zones on the freighter? What are they
7 temp. zones:
-Flight Deck
-Upper deck
-Crew rest
-FWD main deck
-AFT main deck
-FWD lower lobe cargo
-AFT lower lobe cargo
What is a PTC? How many are there?
Pack temperature controller (PTC)
There are 2 of them
How many channels does each PTC have? When does the plane switch between PTCs?
3 channels per PTC (one for each pack)
Normally, the system switches between PTC A or B at touchdown
What does switching a pack control selector from the OFF position to the NORM or A/B position do?
It simply opens the pack valve, allowing bleed air into the pack.
How many different flow rates are there for a pack? When do they change?
2, NORM and HIGH. HIGH flow until TOC, then NORMAL flow until TOD. Or if any pack shuts down, they all go into HIGH.
What is normal flow mode for?
To save fuel so the packs don’t work so hard in cruise. Saves about .3%
How are the 4 engine bleed air switches controlled? (engine bleed valves)
They are electrically controlled, but pneumatically actuated. (When you switch the engine bleed switches on, they will still say closed until the engine is running, at which point the air pressure from that engine can open the engine bleed valve.)
When would air ever be allowed to flow in from the engine bleed valve into the engine, rather than exiting the engine?
Only during engine start.
When would the SYS FAULT lights ever come on for the engine bleed air?
1 of 4 reasons:
1.) High system pressure
2.) High system temperature
3.) If the PRV is open when commanded closed
4.) HP bleed valve open when commanded closed
All 3 packs put out the same temperature. Why is this? How is it determined?
It is determined by the coldest zone. There is no sense in making the packs work harder than they need to.
“Its not which pack you turn on to cool the flight deck the best, its how many.” Why is this statement true?
Because all 3 packs dump into a manifold, so its the number of packs on that determine the flow. More packs, more power to heat or cool.
How do you find out what pack controller (PTC) is in use for a pack?
Pull up the ECS synoptic page, it tells you there.
If PTC A fails, what happens?
It switches to B.
If you have manually selected a PTC, and it fails, what happens?
It switches to A, even though B is selected.
What is the range in degrees that the cabin (passenger variant) and flight deck can be set to by the pack temp selector?
65F (18C) - 85F (29C)
What is the nitrogen generator system (NGS) for? (passenger planes)
Converts bleed air into nitrogen to reduce flammability of center wing tank fuel.
When does the NGS (nitrogen generator system) automatically shut down?
-Engine out
-Equipment cooling to OVRD
-right bleed duct isolated
-cargo fire switch armed
-after landing
What is the pack flow rate determined by?
-position of the Lower Lobe Cargo Conditioned Air Flow Rate selector
-phase of flight
-number of operating packs
What does the FLT FAN switch do?
-When all packs OFF, recirculated cabin air supplied to flight deck
-With at least one pack ON, fan increases flow of conditioned air into the flight deck
-Fan is disabled in flight
For any temperature selector, there is W, C, and MAN. What do these do?
W-Warmer
C-Cooler
MAN- Manual: trim air valve is controlled manually. (in a spring loaded 6 o clock position, you manually adjust the position of the valve to get desired temp).
What does the ZONE RST switch do?
-resets zone temp controller if fault no longer exists
-reopens master trim air valve if duct overheat no longer exists
-reopens forward or aft lower lobe cargo trim air shutoff valve if duct heat no longer exists
On the ZONE RST switch, there is an amber SYS FAULT light that can display on the bottom half of the switch. What would cause this?
-temp zone duct overheat or zone temp fault
-master trim air valve failed closed
-trim air switch off
-master trim air valve closed and pack air continues to flow
There are different zones for temp control. Generally speaking, where is the lower lobe?
It is the very lowest cargo area. Not the main deck (or passenger deck). Its below that. Divided up into 2 zones, forward and aft
For freighters, the main deck and lower lobe temp selection range is____
Between 40F (4C) to 85F (29C)
What does the TRIM AIR switch do?
ON: Automatic and manual selection of temperature is enabled. The master trim air valve is opened and flight deck, upper deck/crew rest, and main deck zones all operate automatically.
OFF: Master trim air valve is closed. Pack output temp is in backup mode
What does the EQUIP COOLING switch do? It has 3 positions: NORM, STBY, and OVRD.
NORM: Draws cabin air into the electrical compartment to cool it. Either exhausts that air into the forward lower lobe cargo or overboard.
Exhausts into forward lower lobe: On ground with engines off and ambient temperature less than 45 degrees.
Exhausts overboard: 2 or more engines running, or ambient temperature greater than 45 degrees.
STBY: Forces exhaust air back inside. (internal closed loop recirculation)
OVRD: Shuts off supply and exhaust fans and valves. Smoke/override valve opens. Equipment cooling dependent on differential pressure. (greater differential pressure=better cooling).
What does the HI FLOW switch do?
If selected ON, all packs go into HI FLOW
What does the AFT CARGO HT switch do?
ON:
-Heats the aft cargo compartment by opening the temperature control valve. Closes and opens to modulate temperature.
OFF: Shuts off aft cargo heat bleed air (no heat provided)
On the AFT CARGO HT switch, there is a TEMP amber light on the bottom half. When would this illuminate?
-Compartment has high temp, and the overheat shutoff valve closes
What does the PACK RST switch do?
Resets pack fault protection system
restarts pack after automatic shutdown if fault no longer exists
On the PACK RST switch, there is an amber SYS FAULT light on the bottom half. When would this illuminate?
-Pack overheat
-System fault
NOTE: May illuminate briefly when automatically or manually switching from PTC channels A or B or B to A
Way up high on the MX overhead panel, there is a LOWER LOBE CARGO COND AIR FLOW RATE switch. It has 6 settings. OFF, FWD LOW, AFT LOW, BOTH LOW, FWD HIGH, AFT HIGH. What do these do?
OFF- No lower lobe pack air is supplied (This is totally different from the equipment cooling stuff. This system allows pack air to heat the lower lobes.)
FWD LOW: 2/3 of pack 3 air given to forward lower lobe
AFT LOW: 2/3 of pack 2 air is given to aft lower lobe
BOTH LOW: 2/3 of pack 3 and pack 2 is given to both forward and aft lower lobes
FWD HIGH: All of pack 3 to forward lobe
AFT HIGH: All of pack 2 to aft lobe
On the pressurization panel, there is a LDG ALT PUSH ON button. What does it do?
Alternates between AUTO and manual mode for landing field elevation.
AUTO: Allows the FMC to determine landing altitude.
Manual: Allows you to increase or decrease the landing altitude value
(Displayed on EICAS)
There is another card asking about the specifics of the trim air button and system, but generally speaking, what exactly is trim air?
Uses hot air off the center manifold and mixes it with cool air leaving the packs to maintain desired compartment temperature. (It mixes hot and cold air until its just right)
On the pressurization panel, what do the MAN switches do?
Manual control of the outflow valves are done by pressing the switch to ON and using the open/close switch. You can do one at a time or both. This bypasses automatic outflow valve control and the cabin altitude limiter (11,000’).
On the pressurization panel, there is a switch titled CABIN ALTITUDE CONTROL and the dial is labeled NORM, A, and B. What does this do?
NORM- Cabin controller A or B is selected automatically on alternating flights
A/B- Manually selects that cabin controller. (If A fails, B takes over regardless of switch position. Same for if B fails, A takes over)
In between the pack dials, there are 2 isolation valves. L ISLN and R ISLN. What do these do?
ON (white bar in view), opens the isolation valve
OFF (no white bar), closes the isolation valve
On an isolation switch, you see an amber VALVE in the top half. What does this mean?
It means the valve position disagrees with the switch position
What does the APU bleed air switch do?
ON- Valve commanded open
OFF- Valve closed
On the APU bleed air switch, you see an amber VALVE on the lower half. What does this mean?
APU bleed valve position disagrees with switch position
What do the engine bleed air switches do?
ON: Bleed air valve opens and the valve, PRV, and HP bleed valve open by system logic once bleed pressure available
OFF: Engine bleed air valve, PRV, and HP valves close (PRV still will open for nacelle anti ice)
What causes a pack to automatically shutdown?
An overheat or a PTC fault
What happens regarding the air system when you arm a cargo fire switch?
pack operation and air distribution is
configured to starve the affected zone of fresh air, minimize air movement, purge
smoke from the flight deck and passenger cabin, and assure the supply of fresh air
to the flight deck.
What is a ZTC?
Zone temperature controller. Controls zone temperatures.
What zones are not supplied off of the trim air system?
The lower cargo lobe areas. These get air directly from the bleed air duct.
If there is a trim air system failure, how is temperature controlled?
-Flight deck temp selector available to PTC: pack outlet temp average 65F-85F
-Flight deck temp selector N/A to PTC: pack outlet temp last flight deck temp setting
-Last flight deck temp N/A= pack outlet temp 75F
Temp control of the lower lobe is not available if ______.
Center bleed duct is isolated
Why should you wait until after start to turn on the AFT cargo heat?
To reduce bleed air demand for engine start
The pressurization system is fully automatic for landing at fields below _____
8,000’
What is a CAC? How many?
Cabin altitude controller (there are 2 of them (A and B))
What protects the fuselage against excessive differential pressure?
Positive and negative pressure relief valves
If cruise altitude is missing from the CAC, what does it assume is your cruise altitude?
39,000’
If landing field elevation is missing from the CAC, what does it assume?
2,000’
What are the 3 modes of the CAC?
Climb, cruise, descent
What is the max cabin altitude in cruise mode?
8,000’
What do the outflow valves do on landing?
Open to depressurize the cabin
The cabin altitude limiter closes both outflow valves when cabin altitude reaches___
11,000’
How many sources of engine bleed air?
- IP (intermediate pressure) and HP (high pressure)
When is IP used and when is HP used?
IP is used during high thrust settings, HP is used during descent and other low power settings.
What is bleed air used for?
-Air conditioning
-Pressurization
-Anti ice
-Engine start
-LE flaps
-Thrust reverser
(also stuff like pressurizing the hydraulic reservoirs, water pressure, and certain demand pumps)
When an engine bleed air overheat is detected___
PRV and HP valves close
When does engine bleed automatically close?
-Ground air connected
-Bleed overtemp
-Bleed over pressure
-Bleed duct leak
-Bleed source loss
-Engine fire switch pulled
During engine start, what happens with bleed air/valves?
-Engine bleed valve opens allowing air IN which opens start valve to power starter
-At 50% N2 the PRV opens and start valve closes
Nacelle anti ice and reverse thrust are normally available, even with the engine bleed air switch off, except for______
-The starter valve failed to close
-PRV failed closed or due to overheat
-HP bleed valve failed open
The APU is used primarily for ________(air system related, not electrical)
Engine ground starting and pack operation
The APU can power 1 pack up to ______
15,000’
Why do isolation valves exist?
To separate the bleed duct system into 3 sections. (Normally all open)
If a bleed duct leak is detected, how can you isolate it?
Using the isolation valve, and the engine bleed valve.
When does the cabin altitude limiter activate? What does it do?
-Activates when cabin altitude reaches 11,000’
-Closes both outflow valves
