I have been doing some simulation flights with the 737-800 and when there is no fuel in the center tank, the engines won't start. Is it like that in real life?
No, it is perfectly normal to operate without any fuel in the center tank. Until your fuel load is over about 17,000 lbs, the center tank should be empty. That’s enough for about 2 hours of flying, plus reserves.
If your simulator requires fuel in the center tank in order to start the engines, it isn’t accurately replicating the real aircraft.
Be sure to turn on the appropriate pumps on the lower-left of the overhead panel. The APU can start without them via suction.
Otherwise, it's a simulator problem.
If you let the center tank go completely dry you’ll get an EMDP malfunction along with an overheat warning. (See ELEC 2 & ELEC 1 hydraulic pump switches on the overhead panel).
The EMDPs are cooled using what are best described as fuel cooled heat exchangers. The temperature sensor for the EMDPs is monitoring the temperature of the case drain fluid, which reflects the source of greatest heat output on a normal pump. There are a number of events that will cause the EMDP to overheat:
- Every time you cycle the pump from OFF to ON, it increases the pump temperature briefly. Cycling the pump off/on repeatedly without allowing adequate time to cool will cause the overheat indication.
- Operating the EMDP without sufficient fuel in the main tanks (from memory: 1,675lbs) will also cause overheating because the fuel quantity is insufficient to provide an adequate cooling mass to the heat exchanger.
- An internal failure of the pump might also cause the overheat light.