Air Systems - Equipment Cooling Show Schematic only

General

There are two separate equipment cooling systems. The forward system cools avionic equipment in the cockpit and the forward Electrical/Electronic (E/E) compartment. The aft system cools equipment in the aft E/E compartment.

Forward Equipment Cooling System

Forward Equipment Cooling System Auxiliary Fan SMOKE Warning Light Alternate Equipment Cooling Switch Equipment Cooling Overheat Light SMOKE in exhaust ducts SMOKE in supply ducts Air Conditioning System Left Recirculation Fan

Forward equipment cooling supplies cooling air to the equipment in the forward equipment racks and the flight deck avionics.

The system has a supply fan that draws cooling air from the cabin and forces it through the equipment racks and avionics. The air is then exhausted into the Air Conditioning Mix Manifold by the Left Recirculation Fan. If the differential pressure is less than 2.5 psi, the Overboard Exhaust Valve automatically opens and most of the air is exhausted overboard.

If the operating fan fails, the alternate fan must be selected.

When the left Recirculation Fan is inoperative, the Overboard Exhaust Valve is automatically opened so differential pressure can produce airflow for equipment cooling.

Equipment Cooling Overheat Light

The equipment cooling OVHT Light illuminates and the EICAS advisory message EQPT OVHT displays if:

When the situation is corrected the light is extinguished and the message canceled.

QRH If the OVHT light remains illuminated:
  • Avionics and electrical equipment and displays not powered by standby buses, are subject to imminent failure.
  • Avionics and electrical equipment on Standby Buses are reliable for 90 minutes. Continued flight beyond 90 minutes can result in loss of essential avionics and electrical equipment.

Auxiliary Fan

ETOPs
An auxiliary fan automatically operates to provide cooling for essential avionics and electrical equipment if the alternate supply fan has been selected but both supply fans are inoperative. However, non-essential avionics and electrical equipment are subject to imminent failure. The Auxiliary Fan can be powered by the Hydraulic Driven Generator.

On the ground, the OVHT light illuminates, the EQPT OVHT message displays and the ground crew call horn sounds if insufficient cooling airflow is detected.

Alternate Equipment Cooling Switch

Alternate Equipment Cooling Switch
ALTN

Equipment Smoke

Equipment Smoke

The Equipment Cooling SMOKE Light illuminates and the EICAS advisory message FWD EQPT SMOKE displays when smoke is detected in the Forward Equipment Cooling System.

The following items, which may be observed in the flight deck, occur automatically to help evacuate the smoke:

When smoke is no longer detected, the Recirculation Fans and Air Conditioning Packs automatically return to normal operation.

Smoke Clearance - Forward System

Forward Equipment Cooling System - Smoke clearance from exhaust ducts Auxiliary Fan SMOKE Warning Light Alternate Equipment Cooling Switch Equipment Cooling Overheat Light Air Conditioning System Left Recirculation Fan - OFF

When SMOKE is detected in the forward equipment Exhaust Duct, the following actions automatically occur:

  • Overboard Exhaust Valve is latched OPEN.
  • (In-flight, Slats UP) LEFT Recirculation Fan is turned OFF
  • LEFT air conditioning Pack is switched to HIGH flow.


Forward Equipment Cooling System - Smoke clearance from supply ducts When SMOKE is detected in the forward equipment Supply Duct, the following actions automatically occur:

  • Overboard Exhaust Valve is latched OPEN.
  • (In-flight, Slats UP) LEFT Recirculation Fan is turned OFF.
  • RIGHT Recirculation Fan is turned OFF
  • BOTH supply fans are turned OFF
  • OVHT light inhibited for 5 minutes (pushing the ALTN switch will start the alternate supply fan)
  • BOTH Air Conditioning Packs are switched to HIGH flow

Aft Equipment Cooling System

AMM The aft E/E compartment contains the:
Aft Equipment Cooling System

Air from the Aft E/E equipment racks is ducted into the Lavatory/Galley Vent System. The vent system exhaust fans discharge the exhaust air in the vicinity of the Outflow Valve.

If fan 1 does not run, fan 2 will automatically provide back-up ventilation.


Cargo Heat