Bleeds, Hydraulics, Air Con and Pressure Flashcards
Isol valve swx in AUTO, where will the valve be?
‘4 corners’ If both bleeds on and both packs in auto the isol valve will be closed. If any one of the 4 corners (bleeds or packs) is swithced off, the valve will open (based on swx posn logic, not actual air pressure)
Where is the bleed system presseure gauge?
Fwd o’head panel
What could cause BLEED TRIP OFF, how to restore?
Overtemp or over pressure, iaw the QRH press the trip reset
What are the sources for the bleed air system? (3)
Engines, APU, gnd starter cart
What services use bleed air?
- Aircon
- pressurisation
- wing and engine TAI
- eng start
- hyd resevoir pressure
- potable water pressure
- aspirated TAT probe
- NGS
Where is bleed air drawn from?
High power = 5th stage compressor
Low power =9th stage compressors
What functions does the Pressure relief shut off valve, PRSOVs have?
Pressure relief shut off valve, regulate pressure and shut off bleed air from the engine at times of critical flight
Which duct is external (pneumatic) air connected?
The right bleed air manifold (don’t confuse with pre conditioned air)
If starter air is connected to the right manifold, which engine do you start first?
The left. The air cart sits on the right away from pax boarding so you have to start the left via the open isolation valve, remove the cart then start the right
Why don’t we select bleeds off for TO to preserve power in critical flight?
They auto switch off
What causes DUAL BLEED?
Left or right bleed being selected on with the APU bleed selected on (swx logic only, not based on pressure)
What is the thrust limit with DUAL BLEED on and why?
Not above idle on the engines to avoid over back pressure damaging the APU
Where are the sensors for the left WING BODY OVERHEAT?
Engine strut, inner LE, air con bay, keel beam and APU duct (right doesn’t have keel or APU)
If a pack fails with the swx in auto what happens?
The other pack goes to high, unless flap not up, in which case it stays in norm to preserve bleed pressure for critical flight
With bleed off what do engine and wing TAI do?
Engine TAI stays on, wing TAI goes off
What does amber OFF SHED DESCENT mean?
You’ve started to descend before reaching your selcted crz alt on the pressurisation panel
From where is conditioned air for the flt deck supplied from?
Normally direct from the left pack, but if failed, from the right pack via the mix manifold
Max height on a single pack?
Boeing 41000ft Company limit FL250
How many packs can an engine run?
1
How many packs can the APU run?
2 on gnd, 1 in flt
How many packs can a ground air cart run?
2
When should packs not be set to high?
Flap not up, critical phases of flight (TO and app)
What does the ram air system do?
Provides extra cooling for the heat exchangers when cold temps are selected
What happens if a primary pack controller fails?
Its run by the stby pack controller in the opposite controller
What do the recirc fans do and what does it do for the Pack?
Pump air from the pax cabin, filter it and return it to the mix manifold. Reduces pack load by 50%
On the gnd where is Electronic & Equipment bay air sent?
Overboards
Is the E&E bay exhaust duct always closed in the air?
No it works on differentail pressure so may be open at low speed
In flt where is E&E bay air sent ?
Around the forward cargo bay liner (not into it) to heat it
If an equip cooling fan fails what can you do?
Follow QRH. Select the alternate
What do you do with a PACK amber fail?
Follow the QRH. Increase all zone temps, then try to reset (PACK – UP)
What do you do if you get a ZONE TEMP warning?
Follow the QRH. Reduce that zone temp and try a reset (DUCT – DOWN)
What does the slosh flap do?
Only open on ground, deflects wheel slosh in bad weather away from the ram air doors
When do the RAM DOOR FULL OPEN blue lights come on?
When ram air doors fully open at high cold demand
Where is pre-conditioned air plugged in?
Direct to the mix manifold (don’t confuse with starter air)
With UFIs fitted, when will a MC illuminate with fuel pump low pressure?
Only if both illuminate (with GFI a single low pressure will cause a MC)
What systems are powered by stby hyd?
LE devices, REVs, rudder, stby yaw
How are you alerted of a bleed air duct hot gas leak?
WING BODY OVERHEAT amber caution
Where does high power bleed air come from?
5th stage only (low power would be 5th and 9th)
Where are the ram air doors during normal use?
They modulate between open and closed
When is the stby system low pressure light armed?
Only when seleted on
When is the stby system low quantity light armed?
Always and will iluminate when half empty
How are the hydraulic reservoirs pressurised?
Bleed air
Why are the hyd reservoirs pressurised?
To prevent fluid cavitation (formation of air bubbles due to pressure changes around pump impeller blades/swash plates)
Which services are powered by system A?
‘’A real giant P’’
AutoP A, rudder, elevators, ailerons, landing gear, gnd spoilers, in flt spoilers, alt brakes, NWS, thrust REV, PTU
What does pulling an eng fire swx do to the hyds?
Closes the hyd fluid shut off valve and deactivates the associated EDP low pressure light
An engine driven pump (EDP) fails, the electro mechanical driven pump (EMDP) continues running. What can you expect?
Intermittant ‘LOW PRESSURE’ on the hyd system running only EMDP. EMDP output is 25% the volume of the EDP (but same pressure, 3000psi) so has trouble with high demand
Why are the switches listed ENG 1, ELEC 2 | ELEC 1, ENG 2?
The electric pumps are powered from the opposite engines. If eng 1 fails, the EDP on 1 fails and the EMDP on 2 fails preserving hyd on both systems
How is hyd from the case drain lines cooled?
Heat exchangers in main fuel tanks (hence min 760kgs in main tanks to swx on the hyd pumps)
EDP on system A (left engine) springs a leak, how is system preserved?
The EDP A feeds from a stand pipe reserving 20% of the hyd fluid for only the EMDP A
EDP on system B (right engine) springs a leak, how is system preserved?
It isnt, both EDP B and EMDP B feed from the same stand pipe so system B will run dry with a down stream leak in either.
However. There is a stand pipe in hyd resevoir B to preserve fluid for the PTU.
Hyd B shows 0% capacity, have I lost PTU assistance?
No, the hyd B fluid resevoir reads 0% at the top of the stand pipe preserving fluid for the PTU.
What does the power transfer unit (PTU) do?
Provides extra volume for LE flap and slat movement at high demand. (ie right engine fail during TO, right EDP stops, hard to raise flap and slats with just EMDP. PTU is driven by left engine hyd A pressure and uses hyd B fluid to raise the LE high lift devices and reduce drag) also allows auto slat operatin approaching the stall
Which switches start the stby hyd pump?
Flt control A or B ‘rud on’ or alt flap ‘armed’ (or activated by FFM)
How would a loss of stby hyd fluid be indicated?
‘LOW QUANTITY’ amber & hyd B would drop to 70% (the stby system is fill to spill from the hyd B resevoir with the feed pipe at 70%)
When does the stby low quantity come on?
<50% capacity
What is the FFM (force flight monitor)?
If differential pressure is detected from hyd A and B at the rudder, the FFM uses stby pressure to correct false inputs (prevents full deflection)
Min / max hyd levels after start?
76 – 97% (below 76% RF (re-fill) is shown)
When do hyd low pressure lights come on?
Circa 50% pressure (1500psi) large margin to account for large service moves such as gear lowering without nuisance warnings
What does the LGTU (landing gear transfer unit) do? (4 and why)
- If engine 1 failed (<50% N2)
- gear lever up
- either main leg not locked up
- Airborne.
- Allows system B to raise the gear in critical stage of flight (left eng fail on TO)
Is there fluid transfer in the LGTU?
Yes the B system fluid used to raise the gear is sent to system A on lowering the gear.
Is there fluid transfer in the PTU?
No. The system A hyd pressure runs the pump on the system B fluid, but both sysytems remain isolated.
What happens when you use the alt flap lowering?
LE flap and slat are immediately lowered to full extension, using stby hyd pressure and cannot be retracted. TE flaps are lowered (slowly) via electrical power
Can you lower the flaps to 40 using alt flap lowering?
Yes, but due to the low raising speed and posibiltiy of excess drag on a GA, max flap 15 max for landing using alt
Limits on alt flap switch use?
Between swx selections min 15 sec to allow clutch cooling. You don’t have to pause at intervals you can go all the way to 15 from UP in one go. If you do a full cycle UP to 15 and back UP, you have to allow 5 mins cooling
What does selecting flt control stby rud ON do?
Starts the stby hyd pump and shuts off the flt control shut off valve for that side isolating rudder, elevator and aileron from main hyd pressure
What does selecting flt control OFF do?
Shuts the flt control shut off valve without starting the sby hyd pump
Why do we leave the EDP switches on all the time?
They are de-energised open, switching them off uses their life and causes failure
What is the max cabin differential pressure?
+9.1 to -0.3psi
What happens at 9.1 diff press?
Cabin alt will increase to prevent explosion (CONTROL DIFF PRESSURE)
In auto when on the gnd does pressurisation start?
As TLs are advanced, the cabin is pressurised to 200ft below airfield elev
What is the cabin pressure on landing?
Pressurised to 200ft below selected landing elevation
What happens if you level off and start descent before reaching your pre selected crz alt on the pressurisation panel?
OFF SCHEDULE DESCENT warning, reset to current level
With the system in auto what are the max diff pressures?
Up to 28000ft = 7.45 psi
Up to 37000ft = 7.80 psi
Up to 41000ft = 8.35 psi (above 8.35 is the amber band)
If auto pressurisation fails what are the indications?
- Amber AUTO FAIL and green ALTN = main failed, switched to alternate and working
- Amber AUTO FAIL only = main failed and failed to swx to alternate, manual required
How do you set the landing alt?
50ft increments, round up to next. E.g. if your landing airfield is 102ft AMSL, set 150ft
How long does a manual valve cycle from fully open to fully closed take?
Circa 20 sec
What is the normal cabin alt at 41000ft?
8000ft
If there’s no AC, what is the APUs power source?
Battery
If the APU’s running and you switch off the battery what happens?
APU shuts down on gnd AND IN AIR
APU EGT exceedance during start, what happens?
Auto shut down
How many AC trans BUSs can the APU power on gnd and in flt?
Both on gnd and in flt (NB both in flt the galleys will be auto shed)
What cabin pressurisation modes are there?
Auto, alternate, manual
What does the pressure relief valve do?
At 9.1 differential will sacrifice cabin alt to prevent further increase in diff press
The auto system has 2 identical controllers, how do you select between them?
You don’t, done in the background without crew input.
What is the limiting diff pressure above 37000ft?
8.35 +/-2
What systems does system B power?
System B: A REAL TOY BAT
Ailerons
Rudder
Elevators
Autopilot B
Leading edge devices
Trailing Edge Flaps
Outboard Flight Spoilers
Yaw Damper
Brakes
Alternate Nosewheel Steering / LTU
Thrust Reverser Right
