Does anyone know what are the two holes are on the Boeing 747, on the left forward part of the fuselage?

enter image description here Source: airliners.net

I guess the right hole is the E/E compartment smoke override valve, is that correct?

Another hole under the belly just before pack inlet:

enter image description here

What is the function or name of this one?


2 Answers 2


The forward opening is the forward outflow valve or forward overboard valve (depending on reference consulted) which opens automatically if airflow in the forward compartment is low. It is independent from the two large aft outflow valves at the lower aft hull used for pressurization.

The second valve is the smoke override valve used in case there is smoke sensed in the the E&E compartment. Basically you try to get rid of the smoke by dumping it overboard. The second function is in case the fans used for ventilation of the E&E compartment fail. Then this valve is opened as well and the differential pressure ventilates the E&E compartment in reverse flow direction. The duct who was supplying the air is now sucking it out of the compartment.

The opening close to the pack inlet on the R/H side is the ground exhaust valve used to dump the air used for E&E cooling on ground overboard in case the temperature is high. This valve is always closed in flight.


  • Boeing 747-400 System Schematic Manual, chapter 21, valves V462 (forward overboard valve), V447 (ground exhaust valve), V448 (smoke override valve)
  • internal documentation provided by employer of the author
  • $\begingroup$ @mins unfortunately I'm unable to share the documentation I have as it is Boeing proprietary or my employer proprietary. If you can get hold of the Boeing 747-400 System Schematic Manual Chapter 21 have a look on schematic 21-58-00 sheet 1. You are interested in the valves V447 & V448. $\endgroup$
    – Chris
    May 27, 2017 at 23:57
  • $\begingroup$ Chris: Your edits look perfect to me. Great answer! $\endgroup$
    – mins
    May 28, 2017 at 8:51

The forward one is exhaust for E&E cooling. The aft one probably is dirt on the camera lens. You can see from the close up that it is a miss shaped circle.

  • 2
    $\begingroup$ It's not on the camera. See jetphotos.net/photo/8445641 jetphotos.net/photo/8433213 and jetphotos.net/photo/8402175 $\endgroup$
    – TomMcW
    Jan 4, 2017 at 0:02
  • 1
    $\begingroup$ Dirt on cameras is always very out of focus in any image. It produces vague blobs that are slightly darker than whatever's in the image, not sharply defined black marks. $\endgroup$ Feb 7, 2017 at 9:48
  • $\begingroup$ Simply not true. Please check your facts before posting. $\endgroup$
    – Chris
    Sep 2, 2019 at 19:23

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