Date: 201412
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Light: Dawn
Aircraft: Large Transport
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Airspace: Class C ZZZ
ATC / advisory: Tower ZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Commercial
Human factors: Situational Awareness; Distraction; Troubleshooting
Anomaly: Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Illness / Injury; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Crew
When detected: Pre-flight
Result: General Flight Cancelled / Delayed; General Physical Injury / Incapacitation
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: The entire flight crew was onboard the plane preparing for the morning flight.  I had completed my walk around was back on the flight deck doing flows and cockpit setup.  The APU was started and several minutes later the captain took a call from the aft flight attendant.  She said she smelled an odor that she described as 'dirty socks.'  The captain left the flight deck to inspect the smell.  I too; noticed an odor now coming into the flight deck.  At first; I thought it may have been some residual deicing fluid from a previous flight and expected this would soon dissipate as it normally does.  Once the captain returned; we discussed the odor.  The smell was stronger in the back of the plane and was not dissipating.  It did not have any 'sweet' smell to it associated with deicing fluid.  In addition; I did not see any deicing residue on the outside of the aircraft during my walk around.  We discussed how the smell had a 'greasy or oily' smell to it.  I thought it similar to an elevator shaft that was freshly lubricated.  Since the smell only started after the APU Bleed was selected on; we concluded that must be the source.  The APU Bleed was selected off and APU shut down.  The captain decided to stop boarding and to have everyone leave the plane.  He communicated with the station; operations; maintenance and the crew.  I went down to the ramp to look at the APU compartment for anything unusual.  When contract maintenance showed up; I was there.  I watched them open the APU compartment access doors.  I estimate I saw 4-8 ounces of oil pour out of the lower door seems when first opened.  The rest of the compartment was coated in fresh looking; shiny oil residue.I returned to the flight deck to get my bags and gear. I was quite surprised how bad it actually smelled.  It was really noticeable after being out in the fresh air and then returning.  I had a very slight headache and was a bit nauseous.  I also had an unpleasant taste in my mouth.  Some flight attendants were complaining of other symptoms too.  The captain spoke with Chief Pilot; Captain.  At his direction we were to be checked out by airport paramedics and then taken to an ER for evaluation.  My symptoms quickly disappeared within a few hours.  I was examined and eventually released with a 'return to work' letter from the ER the same afternoon.  I cleared medical the following day.The captain later spoke with maintenance.  He told me they discovered an oil leak in the APU.  The oil fumes or oil burning fumes must have been pumped into the plane via the APU bleed system.I don't have any suggestions to avoid these types of malfunctions.




Synopsis: Pilot and crew report smelling an odor they associated with deicing; but found it to be an APU that was leaking oil.  Pilot reported being nauseous and having a headache.