Engine Air Bleed — Four Uses, Surge Bleed, TCC/TIC, Three Fire Zones

Starting ran on bleed air. This article takes the engine side of bleed: its four uses, the surge-bleed valves, turbine-case cooling (TCC/TIC), and the three fire-resistant zones. The pneumatic-system side (customer bleed → air conditioning, anti-ice, start) belongs to ATA 36; here only the engine-internal bleed (surge, cooling, sealing) and the interface out to ATA 36.

1. The four uses

The air bleed system is used for : ‐ The pneumatic system (Refer to DSC-36-10-10 General). ‐ Cooling the engine compartment and the turbine. ‐ Cooling the engine and IDG oil ‐ Engine stability.

Per DSC-70-60, bleed serves four ends: ① the pneumatic system (customer bleed → air conditioning / anti-ice, ATA 36); ② cooling the engine compartment and turbine; ③ cooling the engine and IDG oil; ④ engine stability (surge protection). Only ① is bled out; ②③④ are internal.

2. Three fire zones

Per the engine-zones airflow diagram:

 ZONE 1 (front, with the electronic-unit protection box)
   ZONE 1 AIR INLET → … → ZONE 1 AIR EXIT (+ ZONE 1 PRESSURE RELIEF DOOR)
 ZONE 2 (middle, fan / compressor)
   ZONE 2 AIR INLET → … → ZONE 2 AIR EXIT
 ZONE 3 (rear, turbine)
   ZONE 3 AIR INLET → … → ZONE 3 AIR EXIT

The power plant is divided into three primary fire-resistant zones isolated from each other by fireproof diaphragms and seals. Calibrated airflows are supplied to the…

Per AMM 75-21-00, the powerplant is split into three primary fire-resistant zones, isolated by fireproof diaphragms and seals, each fed a calibrated airflow with its own inlet and exit — the basis of the fire design (see Fire Protection Interface).

3. Engine stability — the surge-bleed valves

Two air bleed systems provide greater compressor stability in different flight phases. The volume of airflow through the intermediate pressure and low pressure compressors is regulated by four intermediate pressure stage 8, and three high pressure stage 3, bleed valves controlled by the FADEC. At low engine speed, the bleed valves are open to prevent engine stall.

Per DSC-70-70, airflow through the IP and LP compressors is regulated by four IP-stage-8 and three HP-stage-3 bleed valves, FADEC-controlled, open at low engine speed to prevent stall.

[!note]- How surge bleed works (integrative synthesis across verbatim) At low speed the compressor stages mismatch in flow and tend to stall/surge; bleeding off air from an intermediate stage (IP8, HP3) lowers the back-pressure on the front stages and restores flow matching, preventing stall. Seven valves (4 IP8 + 3 HP3), FADEC-scheduled with speed (the counts are verbatim). This and the IP compressor's VSV are two complementary stall-margin tools (VSV angles vanes, bleed dumps air). Full handling in Stall / Surge.

4. Turbine case cooling (TCC)

TURBINE CASE COOLING (TCC) The TCC system is controlled by the FADEC to improve engine performance by controlling the intermediate pressure turbine blade tip clearance, and cooling intermediate pressure and low pressure turbine cases. The TCC valve is controlled by the FADEC to modulate air flow depending on flight conditions. The valve is fully open in cruise for optimal engine performance.

Per DSC-70-70, TCC controls IP-turbine blade-tip clearance (and cools the IP/LP turbine cases), FADEC-modulated, fully open in cruise for best performance.

[!note]- Why controlling tip clearance improves performance (integrative synthesis) A heated turbine case expands, changing the tip-to-case clearance; a larger clearance leaks gas and loses efficiency. TCC uses cooling air to control case temperature and hold optimum tip clearance — fully open in cruise gives the most cooling, the tightest clearance and the best performance. This reads the verbatim "control blade tip clearance / fully open in cruise."

5. Turbine impingement cooling (TIC)

This system controls the supply of Low Pressure (LP) compressor air to the turbine casing…

Per AMM 75-24-00, TIC controls LP-compressor (relatively cool) air to the turbine casing.

6. Cooling and sealing

Air is removed from different sources in the engine and used to keep the temperature at a satisfactory level. It is also used to seal, and thus isolate, some important parts from others.

Per AMM 75-00-00, bleed from various sources keeps temperatures satisfactory and seals/isolates important parts — covering the fire zones (§2) and bearing-chamber sealing.

7. Counterintuitive points

[!warning]- Surge protection is "bleeding off air," and the valves are open at low speed Counterintuitively, at low speed the seven bleed valves (4 IP8 + 3 HP3) are open to prevent stall (DSC-70-70) — lowering back-pressure, restoring flow matching; they close at high speed. Complementary to the VSV.

[!warning]- TCC is fully open in cruise — for clearance, not just cooling TCC fully open in cruise is for optimum tip clearance (best performance), not simple cooling (DSC-70-70) — it controls clearance, not temperature for its own sake.

Self-test

[!note]- Q1. The four bleed uses — which is external? ① pneumatic system (→ ATA 36, external) ② cool engine compartment + turbine ③ cool engine + IDG oil ④ engine stability (surge).

[!note]- Q2. The surge-bleed valves — how many, from which stages, open when? Four IP-stage-8 and three HP-stage-3, FADEC-controlled; open at low speed to prevent stall.

[!note]- Q3. What does TCC control, and the cruise valve state? IP-turbine blade-tip clearance (also cools IP/LP turbine cases); fully open in cruise for best performance.

[!note]- Q4. How many fire zones, and how isolated? Three, isolated by fireproof diaphragms + seals, each with a calibrated airflow and its own inlet/exit.

[!note]- Q5. What air does TIC use to cool the turbine casing? LP-compressor air (relatively cool).

Key takeaways

Point	Detail
Four uses	pneumatic (ATA 36) + internal: cool compartment/turbine, cool engine/IDG oil, surge
Surge bleed	4 IP8 + 3 HP3 valves, FADEC, open at low speed
TCC	IP-turbine tip clearance (fully open in cruise)
TIC	LP-compressor air to turbine casing
Fire zones	three, fireproof-diaphragm isolated, individual inlet/exit

References

FCOM DSC-70-60 — four bleed uses (pneumatic, cooling compartment/turbine, cooling engine/IDG oil, stability).
FCOM DSC-70-70 — surge bleed (4 IP8 + 3 HP3, open at low speed); TCC (IP-turbine tip clearance, fully open in cruise).
AMM 75-00-00 §1 — bleed cooling and sealing overview.
AMM 75-21-00 §1 — three fire-resistant zones, fireproof diaphragms, calibrated airflows.
AMM 75-24-00 §1 — TIC supplies LP-compressor air to the turbine casing.
Engine-zones airflow diagram — three zones, individual inlet/exit.

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.