What’s the function of the D.C. Start pump
ON
OFF
- A DC Start pump, operated by the START PUMP switch, on the overhead panel, is installed in the right main tank and is used for APU or engine starting when AC Power is not available
- ON - supplies power from 28 VDC TRANSFER BUS to power start pump
- OFF - disconnects 28 VDC Power from starr pump
What’s the function of the RETURN To Tank system on the MD90 only
How is it related to the MD88 overwing heat blankets
- It provides fuel lines which allow the engine heat management system to return fuel heated by the engine and generator fuel – oil heat exchangers to the 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
- Over wing heaters are not installed on the MD90 because of this
When can fuel be transferred
On the ground but not in flight
- the CENTER TANK PUMPS switch on the fuel load control panel under the right wing enables fuel to transfer from center tank when defueling valve is open and fill valve of selected tank is open
How is fuel supplied to the engines with all pumps operating
- 2 AC boost pumps in each main tank
- Crossfeed valve allows either engine to use fuel from either main tank
- 2 AC pumps in center tank installed in series to provide higher pressure so that center tank will be used first
What happens if main tank pumps fail
Engine driven pumps can suck fuel to keep them running but only from the main tanks
What’s the use of the auto position on the center tank fuel switches for alternate fuel burn
- When both are in AUTO position the Alternate Fuel Burn (AFB) will be active
- The AFB System energizes the center tank fuel boost pumps when the center tank fuel quantity is greater than the internal float switch level
- Automatic switching to main tanks occur when center tank decreases to 10000 on the 88, or 3000 on the 90
- The center tank fuel boost pumps are re-energized when either main tank fuel quantity is 4000 on the 88, or 3800-4800 on the 90
- Switches should be on for start, taxi and take off, and placed to auto after take off
- But don’t use auto for any inop boost pump or any abnormal quantity indications
When is alternate fuel burn not required
- On the 88 when over wing heater blankets are good
2. On the 90 when RTT system works
What is the correct response of the fuel quantity display during a fuel quantity test on a MD88
- Each tank digital readout reads 3000 +/- 100
- gROSS WT displays ZFW plus 9000 +/-300
- TOTAL fuel reads 9000 +/-300
How is the D.C. Start pump prevented from overheating
The DC pump does not have overheat protection but is cooled by fuel in the right main tank
