Date: 201807
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Aircraft: A320
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Air Conditioning Distribution System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Human factors: Situational Awareness
Second reporter function: Pilot Not Flying; Captain
Anomaly: Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Illness / Injury; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Attendant
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Diverted; Flight Crew Landed As Precaution; General Physical Injury / Incapacitation
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: While nearing top of climb; flight attendants called the cockpit to complain of an odor emanating from the rear galley that was causing them concern. We performed the 'Elimination Of Odors In The Cockpit/Cabin' checklist; but limited the procedure to the aft cabin/Pack 2 portion of the procedure due to the fact that both the Captain and myself could smell no odor; nor were suffering from any physical/physiological effects.After completing the checklist items; we again established communication with the Flight Attendants and discovered that both the smell; as well as physical/physiological symptoms that they were experiencing; as well as the 'Dirty Sock' smell persisted; we decided to LAND ASAP and ZZZ was selected (with concurrence from Dispatch) as the nearest suitable diversion airport.After briefing the Flight Attendants and Passengers; we diverted to ZZZ and an overweight landing checklist was performed as we were approximately 8000-9000 LBS. over max landing weight. Tower and ground were advised to have EMS meet us at the gate to assist with Flight Attendant and Passenger medical evaluation as needed. Touchdown was smooth and later determined to be well within limits by maintenance. To my knowledge; only one passenger complained of feeling ill; but declined medical treatment; however; all four Flight Attendants complained of feeling nauseous; burning eyes; and dizziness. One flight attendant was observed vomiting in the rear lavatory. After all Flight Attendants were checked at the gate by medical personnel/EMS; they were transported to a nearby medical clinic where it was later learned they had all been diagnosed with Carbon Monoxide Poisoning-with severity ranging from mild to serious. All Flight Attendants as well as Captain performed admirably and professionally during this emergency. All crew members worked together to attain the best possible outcome from unfavorable circumstances that we were presented with yesterday and I have nothing but praise and accolades for our crew.

Callback: The reporter stated that the APU was deferred prior to the flight; therefore; the APU was not operating. The reporter stated that a very strong 'dirty sock' odor was only evident in the aft galley area and; it's as if there was a wall containing the odor only in the aft galley area. The reporter added that all the flight attendants required medical attention and it was determined that each had carbon monoxide poisoning. Only one passenger complained of the odor; but declined any medical attention added the reporter. The reporter stated that they turned off the right hand pack and it didn't seem to make a difference; however; they didn't have time to troubleshoot any further because they were on oxygen and were dealing with landing the aircraft as to not exacerbate the situation. The reporter concluded with stating that that they ferried the aircraft for maintenance; but did not use the packs so there was no odor at that time. Additionally; Maintenance said they did not find any discrepancy; but did a duct burn-out to try and clean the AC ducts.

Second narrative: We were greatly delayed because upon arriving at the aircraft; we found that the APU was deferred and no outside air conditioning was connected. The temperature was about 96 degrees on the aircraft and I told the agent we couldn't board until we cooled the aircraft. After connecting ground air and waiting several minutes; we couldn't get the temperature to drop below about 90 degrees on the aircraft. After contacting the chief pilot; we decided to board all the luggage and below wing items and then start an engine at the gate to cool the aircraft. Finally; we boarded and a short time later departed.When we were within a few thousand feet of top of climb; I received a call from the flight attendants. They stated that they had an odor in the cabin that smelled like dirty socks and that they had been told in recurrent ground school to contact the pilots immediately if they had this issue.We proceeded to find and run the appropriate fumes removal checklist and contacted the flight attendants after waiting an appropriate time for circulation of the cabin air. They stated that the smell did NOT go away and in fact; it might be getting worse. We decided to contact dispatch and divert to another airport. ZZZ appeared to be the best choice and nearest in point of time and after coordinating with dispatch we identified as an emergency and proceeded with haste to ZZZ. We had EMS meet the aircraft in case any passengers were reporting symptoms. The flight attendants had all been exposed and two were quite nauseous. They later were checked at the hospital and found positive for minor Carbon Monoxide poisoning.


Synopsis: A320 flight crew reported diverting after all four flight attendants noted a dirty sock smell in the aft galley area during climb.