737 Air Systems (600/700/800)

The pneumatic system is relied upon for various operations including engine starting, air conditioning/pressurization, wing and engine thermal anti-ice, and pressurization of hydraulic reservoirs and water tanks.

The amber DUAL BLEED Light indicates a possible issue with the APU back pressure. Back pressure can occur when there is a restriction in the airflow, which can lead to reduced performance and potential damage to the APU. To prevent further issues, thrust must be limited to IDLE, which means keeping the engine at its lowest power setting. Therefore, the statement "The amber DUAL BLEED Light indicates a possible APU back pressure condition and thrust must be limited to IDLE" is true.

The blue RAM DOOR FULL OPEN Light illuminates when the Ram Door is fully open.

An illuminated BLEED TRIP OFF light indicates that there is excessive engine bleed air pressure or temperature. This light serves as a warning to the pilot that there is an issue with the engine's bleed air system, which is responsible for supplying air to various aircraft systems. Excessive pressure or temperature can lead to potential problems or malfunctions, and therefore the correct answer is true.

The correct answer is 9.10 psi. This means that the two pressure relief valves are designed to limit the differential pressure to a maximum of 9.10 psi. This is important for safety reasons, as exceeding this pressure could lead to damage or failure of the system. By setting the maximum limit at 9.10 psi, the pressure relief valves ensure that the pressure does not exceed this threshold, providing a safety measure for the system.

The amber OFF SCHEDULE DESCENT Light illuminates to indicate that the airplane has descended before reaching the preset cruise altitude set in the FLT ALT indicator. This means that the aircraft is not following the scheduled descent profile and may be descending too early or too quickly. This could be a result of pilot error or a failure in the altitude control system.

The main source of conditioned air for the flight deck is the Left Pack. This means that the left air conditioning system is responsible for providing the conditioned air to the cockpit. The right pack is not the main source, and both packs and the ground air cart are also not the main sources of conditioned air for the flight deck.

The recirculation fans reduce the load on the air conditioning pack and the demand for engine bleed air. This means that the fans help to decrease the amount of work required from the air conditioning system and the engine, resulting in improved efficiency and reduced energy consumption. By recirculating the air within the cabin, the fans also help to maintain a comfortable temperature and reduce the need for additional cooling or heating. Additionally, the recirculation fans have the capability to detect overheat conditions downstream of the air conditioning packs, ensuring the safety and proper functioning of the system.

The correct answer is approximately 6000 feet. The question asks about the cabin altitude at a cruise altitude of FL 290. FL 290 refers to a flight level of 29,000 feet. The cabin altitude in the manual mode should read approximately 6000 feet, which means that the cabin altitude is maintained at 6000 feet regardless of the actual flight altitude. This information can be determined from the Cabin/Flight Altitude placard.

The statement is true because in the event of a failure of the primary flight deck temperature control system, an automatic switch to the back-up control system will occur. This is a safety measure to ensure that the flight deck temperature remains within the acceptable range for the comfort and well-being of the flight crew. The back-up control system is designed to take over in case of any malfunction or failure of the primary system, providing a reliable alternative to maintain the desired temperature conditions in the flight deck.

The correct answer is Both b and c are correct. This means that the amber DUAL BLEED illuminates when both conditions are met: the APU bleed valve is open and the No.1 engine bleed switch is ON, and when the APU bleed valve is open, the No.2 engine bleed switch is ON, and the isolation valve is open.

Recirculation fans reduce air conditioning pack load. This means that they help to decrease the workload on the air conditioning system, which can improve its efficiency and reduce energy consumption. By recirculating air within the cabin, these fans help to maintain a comfortable temperature without relying solely on the air conditioning packs. This can be especially useful during periods of high demand or when the aircraft is operating at higher cabin differential pressures.

The first engine Bleed Switch is positioned to ON at not less than 400 feet, and prior to 2000 first above field elevation. This means that the switch should be turned on when the aircraft is at a minimum altitude of 400 feet and before reaching an altitude of 2000 feet above the field elevation. This ensures that the engine bleed system is activated at an appropriate altitude during the takeoff phase.

The bleed air switches will be positioned to ON when reaching 1500 feet or until obstacle clearance height has been attained. This is because during a no engine bleed air takeoff, the bleed air switches are typically turned off to preserve engine power. However, in the event of an engine failure, it becomes necessary to turn on the bleed air switches to provide additional airflow for cabin pressurization and other systems. Reaching 1500 feet or obstacle clearance height ensures that the aircraft is at a safe altitude before activating the bleed air switches.

The amber PACK TRIP OFF light illuminates when the temperature in the pack air cycle machine or downstream of the related pack exceeds its limits. Therefore, both options a and c are correct as they both describe possible causes for the illumination of the light.

The engine fan air that is used to cool engine bleed air is discharged overboard. This means that the air is expelled from the engine and released into the atmosphere.

TRIM AIR is added to air from the mix manifold to control zone temperature. This means that the TRIM AIR helps in regulating the temperature within specific areas or zones of the aircraft cabin. It is not used to reduce pack demand, maintain cabin pressure, or control pack temperature.

If any individual zone is switched OFF, it means that the temperature control system will not consider the Temperature Selector setting for that zone. This implies that the temperature in that particular zone will not be regulated according to the Temperature Selector setting. Therefore, the statement is true.

When a zone supply duct overheats, it triggers a safety mechanism that closes the associated Trim Air Modulating Valve. This valve controls the flow of air to the zone, and by closing it, the system prevents further overheating. Additionally, the system illuminates the associated ZONE TEMP Light to alert the operator of the overheating condition. Therefore, the correct answer is that both the closing of the Trim Air Modulating Valve and the illumination of the ZONE TEMP Light occur when a zone supply duct overheats.

An amber PACK Light can illuminate due to two reasons: a pack trip off or the failure of both primary and standby pack control for the same pack. If either of these events occurs, the PACK Light will turn on, indicating an issue with the pack system. Therefore, both options a and b are correct as they represent possible causes for the illumination of the amber PACK Light.

The Engine Bleed Air valves are powered by DC activation and operate pneumatically. This means that they are controlled by a direct current electrical signal and use compressed air to open and close.

The blue RAM DOOR FULL OPEN Light illuminates when the airplane is on the ground and when the Ram Door is fully open. This means that both statements b and d are correct.

The correct answer is "All of the above." This means that all fault indications, including BLEED TRIP OFF, PACK, and ZONE TEMP, can be reset with the TRIP RESET switch.

When the WING-BODY OVHT TEST switch is pressed, the amber WING-BODY OVHT lights illuminate.

When the ISOLATION VALVE Switch is in AUTO, the position of the isolation valve is open when any Engine Bleed Air Switch or Air Conditioning Pack Switch is positioned OFF. This means that the isolation valve will automatically open when either the Engine Bleed Air Switch or the Air Conditioning Pack Switch is turned off. This allows for proper isolation of the engine bleed air or air conditioning systems when necessary.

In the PACK TRIP OFF non-normal procedure, selecting a warmer temperature helps to reduce the workload on the affected air conditioning pack. By reducing the temperature difference between the cabin air and the air conditioning pack, the pack does not need to work as hard to cool down the cabin air. This can help prevent excessive strain on the pack and potentially avoid any further issues or failures.

The bleed air duct pressure indicator is designed to show the pressure in both the left and right bleed air ducts. This means that it can provide information about the pressure levels in both ducts simultaneously. It does not indicate external air pressure or provide information about temperature. Additionally, it does not require DC power for operation.

The motorized Overboard Exhaust valve allows for increased ventilation in the smoke removal configuration. This means that when there is smoke in the aircraft, this valve can be used to increase the amount of air being ventilated, helping to remove the smoke and improve the air quality inside the cabin. The other options mentioned, serving as a backup to the outflow valve and being normally open during pressurized flight above 8000 feet, are not mentioned as functions of the motorized Overboard Exhaust valve in the given information.

If all pack control is lost, it means that there is no control or communication with the pack. In such a scenario, the pack cannot automatically shut down because it does not have the capability to receive or execute any commands. Therefore, the given statement is false.

When a duct overheats, it indicates that the air passing through the duct is too hot. In order to cool down the air, the air mix valves need to drive to full cold. This adjustment allows colder air to mix with the hot air, resulting in a lower temperature. Therefore, the correct answer is that a duct overheating will cause the air mix valves to drive to full cold.

The correct answer is "Related Engine Bleed Air valve." When the amber BLEED TRIP OFF light illuminates, it indicates that the Related Engine Bleed Air valve has automatically closed. This valve is responsible for controlling the flow of bleed air from the engine to various systems.