Narrative:

While turning base to land there was a very strong 'dirty sock' odor detected as we descended through approximately 5;000 MSL. The odor seemed to start shortly after I heard the forward outflow valve open on the aircraft pressurization system. I immediately donned my O2 mask and kept it on until after the engines were shutdown and we were on the gate. I was monitoring the service interphone and I heard the flight attendants discussing the dirty sock odor as well. My first officer placed both recirculation fan switches to the 'off' position and left them there for the remainder of the flight. Since we had the airport in sight and were in the process of being cleared for an approach I made the decision not to consult the qrc/QRH procedure for 'smoke; fire; or fumes in passenger cabin; flight deck or main deck cargo compartment' since I felt the most important task was to get the passengers and crew off the jet as soon as possible in order to mitigate any possible ill effects that could result from the dirty sock odor. To accomplish this task I felt it was necessary to land as soon as possible and I felt that by referencing the qrc/QRH I would be taking the first officer out of the loop in a critical phase of flight when our most important priority was to land the jet and deplane as soon as possible. Also; since there was only an odor and no visible fumes detected; no thought was given to the possibility of ordering a passenger evacuation due to concerns of possible injuries from the evacuation being much worse than simply leaving everyone on the plane for just a few extra minutes and deplaning via the jetway. The odor seemed to start shortly after I heard the forward outflow valve open on the aircraft pressurization system.

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Original NASA ASRS Text

Title: A B737-800 Crew detected a strong dirty socks smell at 5;000' on the approach; so they donned oxygen masks; turned the RECIRC Fans OFF and proceeded to land ASAP. The First Officer felt ill.

Narrative: While turning base to land there was a very strong 'dirty sock' odor detected as we descended through approximately 5;000 MSL. The odor seemed to start shortly after I heard the forward outflow valve open on the aircraft pressurization system. I immediately donned my O2 mask and kept it on until after the engines were shutdown and we were on the gate. I was monitoring the service interphone and I heard the flight attendants discussing the dirty sock odor as well. My First Officer placed both recirculation fan switches to the 'OFF' position and left them there for the remainder of the flight. Since we had the airport in sight and were in the process of being cleared for an approach I made the decision not to consult the QRC/QRH procedure for 'Smoke; Fire; or Fumes in Passenger Cabin; Flight Deck or main Deck Cargo Compartment' since I felt the most important task was to get the passengers and crew off the jet as soon as possible in order to mitigate any possible ill effects that could result from the dirty sock odor. To accomplish this task I felt it was necessary to land as soon as possible and I felt that by referencing the QRC/QRH I would be taking the first officer out of the loop in a critical phase of flight when our most important priority was to land the jet and deplane as soon as possible. Also; since there was only an odor and no visible fumes detected; no thought was given to the possibility of ordering a passenger evacuation due to concerns of possible injuries from the evacuation being much worse than simply leaving everyone on the plane for just a few extra minutes and deplaning via the jetway. The odor seemed to start shortly after I heard the forward outflow valve open on the aircraft pressurization system.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.