Environmental / Bleed Air System Flashcards
What are the primary functions of the bleed air system?
- transfer bleed air from the low- and high-pressure ports to individual system requiring bleed air
- control bleed air pressure
- supply and control temperature of bleed air supplied to the air conditioning system
- supply bleed air for engine starting
- supply bleed air for the wing and cowl anti-ice systems
- supply and control temperature and pressure of bleed air to the air preparation system (APS)
Note, The APS is also known as FITS in the fuel chapter. The first two answers are from the list in the FCOM2, but don’t really answer the question.
What is both the normal and maximum positive relief differential pressure? (AFM Limitations & FCOM2)
Normal: 10.30psi at FL510
Maximum: 10.73psi
What is the maximum negative relief differential pressure? (AFM Limitations)
-0.5psi
What is the maximum differential pressure during taxi and takeoff? (AFM Limitations)
0.1psi
What is the maximum differential pressure upon landing? (AFM Limitations)
1.0psi
What is the maximum altitude AUX PRESS May be used? (AFM Limitations)
41,000ft
Note: this information is in the DUAL AC PACK FAIL checklist.
How is the landing elevation set during QFE operations? (AFM Limitations & FCOM2)
- Must be manually set to 0
- Via the CTP by MIN/LDG, LDG ELEV, MAN
- On any MFW, MISC page, AVIONICS tab
Note: there is a checklist for operating in QFE. QFE is not a memory operation.
Where is the cabin pressure and landing elevation information depicted?
- Below the fuel quantities on the EICAS, or
- On the BLEED synoptic page
Which stages in the high-pressure compressor (HPC) are bleed air extracted?
4th stage LP bleed
7th stage MP bleed
10th stage HP bleed
When is the high-pressure valve (HPV) prevented from opening?
When N2 is less than 55%
Note: the pressure bleed source changes when LP doesn’t provide enough pressure.
During ground operation, what is the priority of bleed sources for engine starting?
(1) APU bleed air
(2) External high-pressure ground connection
(3) Crossbleed
How are bleed air leaks monitored?
Dual loop sensing elements (loop A and B) are routed along the HP ducts and monitored by the IASCs
What occurs automatically when a bleed air leak is detected?
IASCs automatically close the bleed air valve that supplies the affected duct
How is a bleed leak depicted on the synoptic page?
Amber flow lines
The corresponding valves are closed
What happens to the PACK airflow schedule when the heating/cooling demand is high?
PACK FLOW HI schedule is automatically selected by the IASCs to drive maximum airflow
What are the two functions of the air conditioning packs?
- Decrease the air temperature and
- Decrease the water contained in the hot bleed air
When do the IASCs automatically close the flow control valves?
- When a pack fails and
- either the DITCHING PBA is selected on, or
- a pack system fault is detected
Which valves close when selecting the TRIM AIR PBA switch to OFF?
Both hot air shutoff valves (HASOV)
All four trim air valves
What are the two functions of the RAM AIR system?
- Cool the packs and APS heat exchangers
- Alternate source of fresh air at altitudes less than 15,000 ft
What malfunction will require the use of AUX PRESS?
Failure of both packs
Note: a CAS message will take the crew to a checklist
What are the typical cabin altitudes for FL510? FL450?
FL510: Not more than 5,673ft
FL450: Not more than 4,500ft
Note: this is more for pointing how low the cabin is compared to other aircraft. There are several factors governing cabin altitude. These numbers are for illustration purposes only and not an actual accounting of the cabin altitude.
Describe the two modes of operation with the cabin pressure control system (CPCS) in AUTO:
- Primary mode (predictive): FMS has an active flight plan with altitude; autopilot is on, VNAV selected on
- Secondary mode (reactive): uses airplane altimeter and vertical speed (ADC)
During a loss of pressurization, what cabin altitudes trigger the CABIN ALT caution/warning CAS messages for airports below 7,230ft?
CABIN ALT (caution): 8200ft
CABIN ALT (warning): 9000ft
How does the cabin altitude warning system react to airports above 7,230ft?
- CABIN ALT caution and warning thresholds are increased progressively during TO and LDG sequences up to 14,500ft
- A Cyan CABIN ALT HI message is posted.
Note: The Caution will remain 1,000ft above the field elevation until it reaches the maximum value of 14,500ft. The Warning will remain 1,800ft above the field elevation until it reaches a maximum value of 14,500ft.
What is required to display the LDG ELEV in magenta on the EICAS or BLEED synoptic?
Active flight plan with a destination programmed in the FMS
How is landing elevation manually programmed?
- From the CTP: TUNE/MENU, MIN/LDG, LDG ELEV to MAN
- From an MFW: MISC page, AVIONICS tab
When would a pilot need to manually set the field elevation?
- QFE operations
- Airport not in the data base
- Airport not WGS84
Note: Selecting both GNSS to OFF will force the system to navigate DME/DME. Historically this will allow proper navigation in non-WGS84 areas like India.
What occurs when the guarded EMER DEPRESS PBA is selected ON?
- The outflow valves open to depressurize the cabin at a rate of 2,500ft/min
- Cabin altitude will climb to 14,500ft for high altitude airports; 13,800ft for lower altitude airports
What does selecting the DITCHING PBA to ON provide?
- Packs off
- Outflow valves (OFVs) open
- Once cabin is completely depressurized, both OFVs close
Note: the ditching function does not modulate cabin rate at 2,500ft/min, this PBA drives outflow valves full open immediately.
What is the purpose of the safety valves?
Ensures overpressure and negative pressure relief; when max Delta P is reached, the safety valves open to outside pressure, independent from the IASCs
Note: A cyan SAFETY VALVE OPEN CAS will appear when opened
