Date: 201201
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Light: Night
Aircraft: A320
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Physiological - Other; Situational Awareness
Anomaly: Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Attendant; Person Passenger
When detected: In-flight
Result: Flight Crew Diverted; Flight Crew Landed As Precaution; General Maintenance Action; General Declared Emergency
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: While in cruise flight; approximately 20-25 minutes into flight; the Chief Flight Attendant called the cockpit and said that all the flight attendants had noticed a strange smell of 'dirty rancid socks' at about row 6 and further back. All the flight attendants wanted to tell me what they smelled and were clearly concerned. I asked if there actually dirty socks or anything to account for the smell. They reported in the negative. I asked if it smelled like deicing fluid and they said no. (We had deiced prior to takeoff due to moderate accretion of mixed ice on arrival on the previous flight.) I told them that an airport was straight ahead and that we may divert and to keep me updated frequently. I asked the First Officer to contact Operation Control through the Operation Control frequency. Operation Control did not come up under repeated calls. (We later heard that it hadn't been monitored). He then made contact by relaying through Airport Operations frequency. I typed messages to Dispatch informing that we may need to divert and asked if there was a history of fume events on the aircraft. I called back to the flight attendants and asked if the fumes had dissipated. They said it 'may' be less strong; but it was still there. I asked if the passengers had smelled it and they said yes; but had not reported it. They reported that a couple felt ill. Remembering the Union Safety Committee admonition and the Director of Flight's update on the fume events ('We are continuing to address each and every one of these air quality issues by immediately removing an affected aircraft from service.') to treat these events [as a] QRH Fume event and land at the nearest suitable airport; I decided to divert. I was concerned that we; the passengers and crew; were being exposed to TCP neurotoxins. I ordered O2 masks on; transferred control of the airplane to the First Officer to perform the flying duties; declared an emergency; and descended into the divert station. I informed the flight attendants and the passengers that we would be landing as a precaution in 15 minutes due to an unexplained odor in the cabin. There was little time to continue with the QRH Fume procedures or contact our contract medical service. We were vectored by ATC for a visual approach. I saw the runway first and resumed flying duties; landed; taxied to the gate and was met by paramedics. On taxi in I ordered the bleeds and packs to be shutdown. At deplaning; the flight attendants clearly seemed worried about TCP exposure. You could see it in their faces and eyes. We were checked out by paramedics and most of the crew was found to have elevated pulse and BP; and low O2. We declined transport to the hospital; being advised that we should call 911 if we felt ill at the hotel. They strongly recommended that we not continue flying at that time. The flight attendants were surprised after landing because a least two of the passengers; from row 6 and 11; hadn't sought medical treatment from the EMT's. They had reported feeling ill in flight. I faxed a cabin air quality report from the hotel.

Callback: The Reporter stated that because of the heightened 'dirty socks' awareness he did not hesitate to respond to the perceived neurotoxin threat although he First Officer attempted to talk him out of responding. His personal physical condition as determined by the paramedics was slightly elevated blood pressure and pulse; and oxygen level at about 90. The Reporter has been in contact with three other crew members who reported no lingering effects although all were to told to seek medical attention if they felt the need. The Reporter's Company did not report to him what was discovered and he personally wonders if maintenance outsourcing is a component in this problem. He was told that of the 'dirty socks' events; maintenance reported the causes as follows: 58% APU; 30% engine; the remainder unknown.



Synopsis: An A320 Captain declared an emergency and diverted after flight attendants and passengers reported a dirty rancid sock smell from row 6 and beyond. Paramedics discovered elevated BP; heart rate; and low O2 levels.