Narrative:

After takeoff the captain and I noticed a strong (oily) dirty sock odor. We got a call from the aft galley flight attendant station at around 1;500 ft indicating them smelling the (oily) dirty sock smell also. The smell was not decreasing so we donned our O2 masks and established communications. We asked for a level off at 3;000 ft from ATC and notified them of an odor in the aircraft. We declared an emergency. ATC was very accommodating and gave us a choice of runways. We turned off the packs and engine bleeds to eliminate the fumes. When the captain called back to the flight attendants after making a PA the flight attendants said the smell had dissipated. We returned to runway 36. Airfield rescue and fire fighters followed us to the gate and confirmed the aircraft was not smoking and did not have detectable fumes. After we arrived at the gate and the mechanics were onboard they informed us an engine wash was performed when it was overnight. As of this report I am not sure if that was the cause of the smell or it is an actual oil seal in the compressor section. A test is scheduled to be performed later in the day to confirm the cause. In order to possibly prevent this in the future; knowledge of the engine wash would have been helpful in our decision making.

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Original NASA ASRS Text

Title: A B737-800 returned to land after takeoff because a strong dirty socks odor was detected in throughout the aircraft. Maintenance stated an engine wash was completed the previous night so the odor may be a chemical residue.

Narrative: After takeoff the Captain and I noticed a strong (oily) dirty sock odor. We got a call from the aft galley Flight Attendant station at around 1;500 FT indicating them smelling the (oily) dirty sock smell also. The smell was not decreasing so we donned our O2 masks and established Communications. We asked for a level off at 3;000 FT from ATC and notified them of an odor in the aircraft. We declared an emergency. ATC was very accommodating and gave us a choice of runways. We turned OFF the packs and engine bleeds to eliminate the fumes. When the Captain called back to the flight attendants after making a PA the flight attendants said the smell had dissipated. We returned to Runway 36. Airfield Rescue and Fire Fighters followed us to the gate and confirmed the aircraft was not smoking and did not have detectable fumes. After we arrived at the gate and the mechanics were onboard they informed us an engine wash was performed when it was overnight. As of this report I am not sure if that was the cause of the smell or it is an actual oil seal in the compressor section. A test is scheduled to be performed later in the day to confirm the cause. In order to possibly prevent this in the future; knowledge of the engine wash would have been helpful in our decision making.

Data retrieved from NASA's ASRS site as of July 2013 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.