Fuel

Question 1

(88, 90) Function of DC start pump:

Answer 1

• A DC Start Pump, operated by START PUMP switch on the overhead panel, is installed in right main tank - used for APU or engine starting when AC power is not available.
• ON – Supplies power from 28VDC TRANSFER BUS to power start pump.
• OFF – Disconnects 28VDC power from start pump.
• The start pump does not have overheat protection, but is cooled by fuel in right main tank.

Question 2

(90) Function of MD-90 Return To Tank system (RTT):

Answer 2

• RTT system provides fuel lines which allow engine heat management system to return fuel heated by engine and generator fuel-oil heat exchangers to main fuel tanks.
• RTT reduces the likelihood of wing ice caused by cold-soaked fuel while improving the efficiency of the engine heat management system.
• Overwing heaters are not installed on the MD-90 due to the RTT system.

Question 3

(88, 90) Can fuel be transferred on the ground? In flight?

Answer 3

• The CENTER TANK PUMPS switch on the Fuel load control panel under right wing enables fuel to transfer from center tank when defueling valve is open and fill valve of selected tank is opened
• Fuel cannot be transferred in flight

Question 4

(All) How is fuel supplied to engines with all pumps operating?

Answer 4

• Each main fuel tank has 2 AC boost pumps installed in parallel.
• Interconnect system and crossfeed valve between fuel tank systems permit use of fuel from either main fuel tank to both engines.
• The 2 AC center tank pumps are connected in series to provide pressure higher than main tank pumps, ensuring usage of center tank fuel even with both main tank pumps operating.

Question 5

(88, 90) Can engine driven fuel pumps suction feed fuel to engines? From which tanks?

Answer 5

• Engine driven fuel pumps are capable of suction feeding fuel to engine from main tanks only.

Question 6

(88, 90) Explain the use of auto position on the center tank fuel switches for alternate fuel burn:

Answer 6

• With pump switches in AUTO, Alternate Fuel Burn (AFB) system is active.
• AFB system energizes center tank fuel boost pumps when center tank fuel quantity > internal float switch level.
• Automatic switching to main tanks occurs when center tank quantity decreases to approx 10,000 lbs (MD-88) or 3,000 lbs (MD-90).
• Center tank fuel boost pumps are re-energized when either main tank fuel quantity is approx 4,000 lbs (MD-88) or 4,800 to 3,800 lbs (MD-90).
• Switches should be ON for start, taxi and takeoff and placed to AUTO after takeoff (if applicable).
• Do not use the AUTO position for any inoperative boost pump or any abnormal quantity indications.

NOTE: Alternate Fuel Burn is not req’d on MD-88’s w/ operable overwing heater blankets, nor on MD-90’s with operable Return To Tank (RTT) system.

Question 7

(88) What is the correct response of the quantity display during a fuel quantity test on an MD-88?

Answer 7

• Each tank digital readout displays 3,000 ± 100.
• Total Fuel displays 9,000 ± 300.
• GROSS WT displays ZFW plus 9,000 ± 300.