A Typical Day — ATA 21 Through a Flight

This article strings the previous articles into a timeline — every ATA 21 action from a cold aircraft to shutdown. The application chapter: at each phase, which ECAM the pilot reads, which button is pressed, which selector is set, all tied to the engineering learned earlier.

1. The nine phases & the control default states

   cold aircraft power-up → APU + packs on → engine start → taxi → takeoff + prepressurisation
   → climb → cruise (ECAM scan) → descent (CPC + LDG ELEV) → landing (80 s) → parking (shutdown)

[!note]- The cold-aircraft default states

Unpowered, the electric valves sit at their no-power positions: the outflow valves fully open (spring + default open), the safety valves closed, the PFCVs closed (no bleed + spring), the AEVC overboard valve closed, the cargo isolation valves closed, the CPC unpowered. This is the ground-mode default — cabin = ambient, all openings closed except the outflow valves fully open for ventilation. On power-up the CPC + the valve controllers energise and wait for the packs to start.

2. Cold aircraft → packs on

Cockpit preparation (per the SOP): set LDG ELEV AUTO, PACK FLOW as required, HOT AIR + CAB FANS ON, EXTRACT AUTO, GND COOL AUTO, and the cargo temperatures as required.

PACK FLOW selector AS RQRD. SELECT: LO if less than 60 % of the seats in the economy class are occupied, but not more than 200 passengers in all classes. HI for abnormally hot and humid conditions. NORM for all other normal operating cases. If APU is supplying, pack controllers select HI flow automatically, independently of selector position. — FCOM PRO-NOR-SOP-06

[!important]- PACK FLOW selection — economy < 60 % and < 200 passengers

NORM flow is sized for a full load (~300+). With far fewer passengers, NORM wastes bleed → select LO to save fuel. LO needs both: economy-class occupancy < 60 % and fewer than 200 passengers total. Otherwise NORM; abnormally hot/humid → HI. When the APU supplies, the selector is overridden to HI (the APU bleed is weaker and farther from the cabin, so HI is needed for sufficient flow).

[!tip]- The PRESS pb LDG ELEV test

PRESS pb PRESS. Check that the CAB PRESS SD page displays LDG ELEV AUTO to confirm correct position of the LDG ELEV knob. — FCOM PRO-NOR-SOP-06

An important cockpit-prep test — confirm the CPC uses the FMGS automatic landing elevation (not a leftover manual value).

After the APU starts (APU GEN + APU BLEED ON), PACK 1 + 2 pb ON: the APU bleed → cross-bleed valve → PFCV → packs → cabin. Confirm on the SD BLEED page: the PFCVs green/inline (open), the pack flow HI (the APU forces HI), the pack-outlet temperature green. ~30–60 s later the cabin has a noticeable airflow — the passengers' first air-conditioning at boarding.

3. Engine start

PACK pb On: It opens, except in the following cases — Engine start sequence: One valve (or both, if the crossbleed valve is open) closes when MODE selector is set to IGN and (on either engine) MASTER switch ON and start valve open and N3 < 50%. — FCOM DSC-21-10-50

[!warning]- The packs auto-close at engine start — why

Engine start needs bleed to drive the starter → cabin pack bleed would compete with the starter → a hard start. The PFCV closes to give all the bleed to the starter. Once the start completes (N3 > 50% / start valve closed), the PFCV restores automatically — no pilot action. So a brief ECAM PACK 1(2) OFF during the start is normal (the same warning as a pilot-selected OFF in ata-21-21, but a system auto-close, not a fault); it self-restores in ~1 minute.

After both engines start, APU MASTER + APU BLEED OFF (save the APU), the bleed source switches from APU to the engines, the packs re-supply from engine bleed, and the PACK FLOW de-selects HI (per the selector). On taxi, scan the SD: the PFCVs green, the pack flow NORM, the temperatures regulating; the CAB PRESS SD reads ~0 cabin altitude / V/S / ΔP.

4. Takeoff & prepressurisation

[!important]- Takeoff PACK OFF (some operators) — why

Some operators' SOP requires switching the PACKs OFF before takeoff for: a high-altitude airport (insufficient thrust margin), a heavy / short-runway takeoff, or a max-thrust (TOGA) takeoff. The packs draw bleed → ~1–2 % thrust loss; switching them off at the performance limit recovers that thrust. The specific cases are in the operator SOP (not the FCOM). On the takeoff roll, some ATA 21 L2 warnings are inhibited (avoiding distraction); L3 warnings (EXCESS CAB ALT / SMOKE / FUMES) are never inhibited.

[!important]- Prepressurisation

Before lift-off the CPC prepressurises — giving the cabin a small positive ΔP (~0.1 PSI) so that at lift-off it does not jump from ΔP = 0 to ΔP > 0 (avoiding an ear-pressure step). It does this by slightly closing the outflow valves on the takeoff roll. The pilot feels nothing — automatic, no control, no ECAM.

In the climb, the cabin V/S is ~400 ft/min while the aircraft V/S is ~2000 ft/min (a ~5:1 ratio from the CPC schedule) — slow cabin-pressure change for ear comfort.

5. Cruise, descent, landing & parking

[!tip]- The cruise ECAM scan — four CAB PRESS fields

Every 15–30 min, scan the SD CAB PRESS page:

Field	Normal	Abnormal
CAB ALT	per schedule (FL 350 ≈ 6500 ft)	red > 9550 ft
CAB V/S	≈ 0 (cruise stable)	pulsing > 1800 ft/min
ΔP	7–8 PSI (cruise)	amber < −0.2 / > 8.85
OFV position	partly open (~30–50 %)	full open / closed

Plus the SD BLEED page: the PFCVs green, the pack flow NORM, the compressor outlet below 180 °C.

[!note]- The CPC descent schedule

The CPC uses the FMGS landing elevation + the current aircraft altitude + V/S to compute a cabin-altitude target schedule (the cabin altitude = the field elevation at landing). The cabin V/S is ~300–400 ft/min for a ~2000 ft/min aircraft descent. The pilot does not touch the LDG ELEV knob — the FMGS feeds it automatically; only on an FMGS failure (ata-21-23) or a diversion does the pilot set it manually.

[!important]- 80 s after touchdown

80 s after touchdown (ground mode confirmed) the CPC: fully opens the outflow valves (full depressurisation), adjusts the pack flow, and swaps the active CPC (the next takeoff uses the other CPC as primary, ata-21-11). The 80 s is a ground-stable window — avoiding a touch-and-go falsely triggering ground mode.

At parking: the APU starts + APU BLEED takes over the cabin ventilation, the engine masters go OFF (the bleed source switches engine → APU so the cabin ventilates uninterrupted while the passengers disembark), then ground power + the APU shut down (GND COOL if the OAT is high).

[!tip]- The rhythm — ATA 21 is ~80 % automatic

The pilot's actual ATA 21 actions cluster at three points: cockpit preparation (five button settings), the APU bleed start (PACK 1+2 ON), and parking (the APU-bleed handover). The rest is monitoring + reacting to abnormals — which is why the abnormal + MEL articles fill half this material; the pilot is only truly "busy" in the abnormal. ATA 21 is like a car's automatic climate control — set it before driving, then automatic; manual intervention only on a fault.

Self-test

[!note]- Q1. What are the conditions to select PACK FLOW LO at cockpit preparation?

Both, together: economy-class occupancy < 60 % and fewer than 200 passengers total. If either fails → NORM; abnormally hot/humid → HI. When the APU supplies bleed, the selector is overridden to HI.

[!note]- Q2. ECAM PACK 1 OFF during engine start — a fault?

No — a normal system inhibit. The PFCV auto-closes to give the bleed to the starter; it restores after N3 > 50%. No pilot action — wait for the start to complete.

[!note]- Q3. What is the purpose of a takeoff PACK OFF, and when?

To recover the ~1–2 % thrust the packs draw → more takeoff performance margin. When: a high-altitude airport, a heavy / short-runway takeoff, or a max-thrust (TOGA) takeoff. The specific cases are in the operator SOP (not the FCOM).

[!note]- Q4. The normal cruise values on the SD CAB PRESS page?

CAB ALT per schedule (FL 350 ≈ 6500 ft, FL 380 ≈ 7000 ft); CAB V/S ≈ 0; ΔP 7–8 PSI; OFV partly open (~30–50 %). Abnormal: CAB ALT > 9550 ft red / CAB V/S > 1800 ft/min pulsing / ΔP < −0.2 or > 8.85 PSI amber.

[!note]- Q5. What does the CPC do 80 s after touchdown?

Three things: fully open the outflow valves (full depressurisation), adjust the pack flow, and swap the active CPC (the next takeoff uses the other as primary). The 80 s is a ground-stable window avoiding a touch-and-go false trigger.

Key takeaways

Common misconceptions

Scope — what this article covers and defers

References

A330 specifics per FCOM PRO-NOR-SOP-06 (the cockpit-preparation ATA 21 button settings, the PACK FLOW LO/NORM/HI selection with the economy < 60 %/< 200 passengers rule and the APU HI override, and the PRESS-pb LDG ELEV AUTO test), FCOM DSC-21-10-50 (the engine-start PFCV auto-close at MODE IGN + MASTER ON + start valve open + N3 < 50 %), FCOM DSC-21-20-30 (the prepressurisation), FCOM DSC-21-10-30 (the PACK FLOW selection + APU override), and FCOM DSC-21-10-40 (the active-CPC swap at touchdown + the 80 s ground mode). The cold-aircraft default states, the ~5:1 cabin-V/S ratio, the three-action rhythm, and the parking-handover reasoning are integrative syntheses; the takeoff-PACK-OFF cases are noted as operator-SOP, not FCOM. All engineering detail is from the A330 knowledge base; the procedures are presented generically without operator-specific SOP, no cross-type comparison is made, and no fleet tail numbers appear.

Independent study material, not an Airbus publication and not endorsed by the manufacturer. Always defer to the current operator FCOM, FCTM, and QRH for operational use.