21. Boeing 737NG - Fuel System

Summary

This comprehensive guide explains the Boeing 737's fuel system, covering its main and center fuel tanks, pump operations, and shutoff valves. It outlines standard procedures for fuel management during pre-flight, flight, and post-flight, including troubleshooting common issues like fuel imbalances, configuration alerts, and low fuel warnings. Detailed instructions are provided for correcting fuel imbalances, managing the fuel system, and responding to non-normal conditions. The video aims to help operators understand the critical role of fuel distribution, ensuring safe and efficient flight operations.

Takeaways

• 😀 The 737 airplane has three fuel tanks: two main tanks in the wings (each with a capacity of 8,630 lbs) and one center tank in the fuselage (with a capacity of 28,803 lbs).
• 😀 The main tanks supply fuel to engines 1 and 2, with the left main tank supplying engine 1 and the right main tank supplying engine 2.
• 😀 The center tank has higher output pressure than the main tanks and is used first before the main tanks' fuel.
• 😀 Each main tank uses two electrical pumps (forward and aft), while the center tank uses two boost pumps (left and right).
• 😀 The cross-feed valve allows fuel from one main tank to supply fuel to the opposite engine if needed.
• 😀 The engine and spar fuel shutoff valves are electrically controlled and prevent fuel flow to the engines in the event of an emergency.
• 😀 The fuel control panel, located on the forward overhead panel, is used to operate the fuel pumps and manage the fuel system during flight operations.
• 😀 The low-pressure light on the fuel pump switches illuminates when the output pressure is low or when the switch is in the off position.
• 😀 For normal flight operations, the fuel system needs to be balanced between the main tanks, and the difference in fuel between the tanks should not exceed 998 lbs.
• 😀 During non-normal conditions like fuel imbalance or low fuel, amber alerts are triggered on the fuel quantity indicators, signaling the issue that needs to be addressed.

Q & A

What is the total usable fuel capacity of the 737's fuel tanks?

The 737 has three fuel tanks: the two main tanks (1 & 2) each have a usable fuel capacity of 8,630 lbs, and the center tank has a usable fuel capacity of 28,803 lbs.

How is fuel supplied to each engine on the 737?

Engine 1 is supplied by Main Tank 1 and the Left Center Fuel Pump, while Engine 2 is supplied by Main Tank 2 and the Right Center Fuel Pump.

What is the purpose of the cross-feed valve in the 737's fuel system?

The cross-feed valve allows the main fuel tanks to supply fuel to the opposite engines when necessary, providing flexibility for fuel management.

What happens if the output pressure of a fuel pump is low?

When the output pressure is low, a low-pressure light illuminates on the fuel control panel to alert the crew. This occurs if the fuel pump switch is on but the pressure is not normal.

What happens when the center tank fuel pumps have failed and no fuel is available in the center tank?

In such cases, the mechanical engine-driven fuel pump will supply suction fuel feed through a bypass valve in the main tanks, as the center tank lacks a bypass valve.

What should be done during pre-flight to ensure the fuel system is ready for engine start?

During pre-flight, ensure the Engine Valve and Spar Valve closed lights are dim, the filter bypass light is off, and the fuel pumps for tanks containing fuel are activated. Also, the cross-feed valve should be closed.

What is the maximum allowed imbalance in fuel between the two main tanks?

The maximum permitted difference in fuel quantities between the two main tanks is 998 lbs. If the imbalance exceeds this, an amber imbalance alert is shown on the fuel indicator.

How is fuel imbalance managed during extended APU operations?

During extended APU operations, fuel from the center tank is used to prevent fuel imbalance. This ensures that both main tanks remain balanced.

What actions should be taken if an in-flight fuel imbalance is detected with fuel in the center tank?

To correct the imbalance, first turn off the center tank fuel pumps, open the cross-feed valve, and monitor the fuel quantities until balanced. Then, turn on the main tank fuel pumps, turn on the center tank pumps, and close the cross-feed valve.

What is indicated by the 'filter bypass' light, and what action should be taken?

The 'filter bypass' light illuminates when there is an impending filter bypass due to contamination. This signals a potential issue with fuel quality, and the system will alert the crew to take corrective action.