This system is closely linked to the Air Conditioning system which we discussed back in episode 2. If you havent listened to it already it may be worth going back and listening to that first.
The main components. The system consists of:
- Two Cabin Pressure Controllers (CPCs)
- One Residual Pressure Control Unit (RPCU) (if fitted)
- One outflow valve, with an actuator that incorporates three motors (two for automatic operation, one for manual operation)
- One control panel
- Two safety valves.
To work out the schedule, the current CPC uses the landing elevation and the QNH we've entered into the perf page of the FMGC, and the pressure altitude from ADIRS.
If FMGC data isn't available, the controller uses the captain BARO reference from the ADIRS and the LDG ELEV selection from the overhead panel.
The system follows a schedule for each flight which consists of four general functions:
- Ground function: It Fully opens the outflow valve on ground
- Pre Pressurisation :During takeoff, it increases cabin pressure to avoid a surge in cabin pressure during rotation (we'll talk about whether this really ever happens later)
- Pressurisation in flight :It Adjusts cabin altitude, and rate of change to provide passengers with a comfortable flight
- Depressurisation :After touchdown, it gradually releases residual cabin overpressure before the ground function fully opens the outflow valve.
Scenario of the Week
You get a call from the Cabin, they are complaining of a loud noise coming from door 2L (at the back).
What is OEB48? Well basically it's an Operations Engineering Bulletin that was issued by Airbus to all operators to cover the possibility of all AoA probes becoming "blocked" which could then cause the aircraft to go into unwanted protections.
The reason αprot decreases with mach number is due to two things, compressibility effect and critical mach number. Above about Mach 0.6, Calibrated Air Speed and Equivalent Air Speed diverge due to compressibility effects, meaning CAS over-reads compared to EAS. Airbus and most other aircraft PFDs show CAS on the airspeed tape, so at higher Mach numbers the Vls, aProt and aMax displayed must increase to compensate for the growing difference between EAS and CAS. The other effect is caused by increasing the Mach number into the transonic range. This eventually causes small shockwaves to form on the wing, which grow in size as the flight Mach number and/or AOA increase. These shockwaves disturb the airflow behind them, reducing the lift of the wing compared to subsonic flight conditions for the same AOA. The relationship between CL and AOA are adjusted to compensate. The effect is the stall equivalent airspeed increases because the shockwaves cause CLmax to decrease.
Finally, the shockwaves can also cause the wing to stall at a lower AOA, but this is all dealt with through reduced CLMax and thus higher stall speed.
CAS Link https://en.wikipedia.org/wiki/Calibrated_airspeed
EAS link https://en.wikipedia.org/wiki/Equivalent_airspeed
Critical Mach Number link https://en.wikipedia.org/wiki/Critical_Mach_number
Accident interim report for Lufthansa Accident http://www.bfu-web.de/EN/Publications/Interim_Reports/IR2014/I1_Report_14_6X014_A321_Pamplona.pdf?__blob=publicationFile
Every Summer when we both have our LOE simulator tests we will give you a run through of what we had and how we dealt with it.
The events Matt had were,
- ACP 2 failure
- FWC 1&2 fault
- FCU 1&2 fault
The events Andy had were,
- Auto thrust
- ADR 1&2
- Direct law go around
www.a320podcast.com/podcasts/summer16
This week we look at the Air Asia accident where the crew ended up loosing control of the aircraft at high altitude. We've saved you the effort of looking at the 200+ page report but if you wish to read it fully yourself then you can download it by going to the following link,
The episode has the details of the event but below are some points to take away from this event.
We can’t prevent external factors like a dodgy solder joint or engineers not fixing an issue but we can minimise those effects on our flight and, as we've already mentioned, there are some fundamental rules which if the crew had followed this accident wouldn't have happened.