As part of the start up sequence for the F-16, the "air source knob is set to NORM", according to this source:


What is "NORM"? And what is "DUMP" and "RAM" and "OFF"? When are these different settings used? What does this actually control?

I can't imagine that the actual air intake for the engine can actually be closed with "OFF"? The other options also makes no sense to me. Is there any variable geometry on the air intake on the F-16?

Will the engine only start in "NORM" or is it just easier to start in "NORM"?

  • $\begingroup$ It appears to me that you are looking at the wrong image. You are looking at the fuel panel. The "air source" knob is on the air conditioning panel (the next image), and it appears to be for pressurization control. $\endgroup$ Commented Oct 7, 2023 at 11:44
  • $\begingroup$ @AdityaSharma Thanks for that! I was indeed looking at the wrong picture. Corrected it now in my question. I still don't understand though, is this really for air conditioning? Is that an essential part of starting the F-16? $\endgroup$ Commented Oct 7, 2023 at 14:06

1 Answer 1


That’s the engine bleed air control system in the aircraft. It controls bleed air from the engine for cabin pressurization, anti-G, canopy seal, fuel tank pressurization, and air conditioning as well as the cabin pressurization dump valve.

OFF - engine bleed air valve is closed. Deactivates all the systems listed above.

NORM - engine bleed air valve is open and providing pressurized air for cabin pressure and air conditioning.

DUMP - cabin air dump valve is open. Bleed air functions to ventilate cabin and can provide a slight pressure boost above 8000 feet MSL.

RAM - engine bleed air valve is closed and cabin dump valve open. Cabin is ventilated by ram air through an exterior scoop.

This is not closing or shutting off air supply to the engine, but rather the cockpit and other systems that rely on bleed air from the engine to operate. Bleeder valves are often left open during start up, as this presents less resistance from the compressors, when the JFS crank the engine, and allows the engine to build up core speed much more quickly during startup. Apparently, the F-16 is started up with those systems in operation.

  • $\begingroup$ If F-16 sims DCS and BMS are to be believed, this setting also enables air intake used to cool the avionics, and if you fly with it off you risk breaking the avionics due to overheating. $\endgroup$ Commented Oct 12, 2023 at 3:41
  • $\begingroup$ The real issue here would be the fire control radar (FCR), which is cooled by the bleed air environmental control supply. If, for any reason, the bleed air system had to be shut off, it would be advisable to turn the FCR off as well. It is possible you could use the FCR for short periods of time w/o bleed air operational, but a flight crew should monitor the warning light display for a EQUIP HOT caution and shut off the FCR immediately, should it become illuminated. $\endgroup$ Commented Oct 14, 2023 at 15:00

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