Originally Posted by
Dave Therhino
It's been 20 years since I was in the cockpit of a 777 (as an engineer in flight testing - not a pilot) but here is what I recall. Hopefully someone else can confirm or correct this.
The PRESS light on the fuel pump switches means low pressure. However, unlike the main tank boost pumps, the center tank pump low pressure lights are inhibited if the pump switches are off because normal operation of the airplane includes operation with those switches off (after the center tank is depleted of if there is no mission fuel in the center tank). The Boeing "dark cockpit" approach is to not have lights illuminated on the overhead panel for normal conditions. If you look at the switches with electrical power on airplane but all pump switches off, the main tank boost pumps switches will have the PRESS lights illuminated but the center tank pump switches will not. If the center tank pump switch is on but the pump output pressure is low due to lack of fuel or a pump failure, the PRESS light will be illuminated.
this sounds right for the 787, which I believe is the same as the 777.