Date: 201409
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Dawn
Aircraft: EMB ERJ 190/195 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class A ZZZ; Class B 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
Anomaly: Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Crew; Person Flight Attendant
When detected: In-flight
Result: Flight Crew Returned To Departure Airport; Flight Crew Landed As Precaution; General Declared Emergency
Contributing factors: Human Factors; Aircraft
Primary problem: Aircraft

Narrative: Upon arrival at the aircraft the First Officer informed me that the #2 engine had a fuel leak and the circuit breakers for the #1 and #2 engine igniters were popped. I notified maintenance and made a logbook entry. Maintenance personnel ran the #2 engine momentarily at the gate and the fuel leak stopped and we began boarding passengers. During climb we noticed a foreign smell in the cockpit. Once above 10000 ft AGL the First Officer called the cabin crew to ask if they smelled anything. They each described the same smell that we had in the cockpit. The smell never seemed to dissipate and was getting stronger. It had a wet mold or musky smell that resembled dirty socks or severe body odor. I had never smelled this odor on an airplane like this before. I called the cabin crew once again and the lead Flight Attendant reported a developing headache. My First Officer (FO) reported feeling light headed. We donned our oxygen masks and leveled at 24000 ft. We [advised] ATC and received a clearance to return to ZZZ. I notified the flight attendants that we were returning to ZZZ and would be on the ground in 10 minutes. I sent an ACARS message to dispatch and told them we were returning. I had the FO fly the airplane while I opened the QRH for assistance. We could not readily identify the source of the smell and had no other cockpit indications. I proceeded to set up the MCDU for arrival into ZZZ and changed the destination runway to 27L. Our landing weight was 103000 lbs which is 6000 lbs over max landing weight. We maintained maximum forward airspeed to expedite our landing. After setting up for the approach and briefing for the landing I proceeded with the overweight landing checklist and then the descent and approach checklist. I checked the overweight landing performance and flaps 5 was selected for landing on the longest runway. By this time we were very close to landing and I took my Oxygen mask off momentarily to see if the odor was still there which it was. With very little time left I started the Smoke/Fire/Fumes QRH procedure but elected to discontinue the procedure to make the landing since the FO was feeling light headed. I landed on 27L with a descent rate of 200 fpm or less and exited the runway. We elected to proceed to gate to deplane the passengers and had EMT personnel meet us at the gate in case any of the passengers needed assistance. I made a logbook entry for the overweight landing and the unidentified odor. The entire crew proceeded to the hospital where we were evaluated and then released. At no time was smoke present and the source of the acrid odor could not be identified. I have no idea why this odor was present in the aircraft. I have never smelled this odor on the airplane before. The aircraft had been in ZZZ all night and maintenance had worked on the aircraft at some time during the evening. This was the first flight of the day for this aircraft.




Synopsis: During climb; an ERJ-190 flight crew detected a wet mold or musky smell that resembled dirty socks or severe body odor. After leveling at FL240 and being unable to find the source of the odor; the crew elects to return to the departure airport.