Date: 202007
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent; Parked
Aircraft component: Air Conditioning Distribution System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Troubleshooting
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Attendant; Person Flight Crew; Person Other Person
When detected: In-flight; Pre-flight
Result: Flight Crew Overcame Equipment Problem; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Ground air was hooked up to the aircraft several minutes after the aircraft arrived in ZZZ with the APU running the Packs. Ground power was not provided. I and the FO (First Officer) entered the terminal for a few minutes and upon return the first Flight Attendant said the cabin had an odor from the air conditioning. The smell was the familiar 'dirty sock' or 'dirty; musty' smell that had been an issue with the fleet in the past related to the APU oil issue.I deactivated the APU Bleed to see if the ground air would clear out the odor. The boarding process also began; and the third Flight Attendant said the passengers were noticing the order. Attempted to contact maintenance on the frequency listed on the 10-7. No response. Contacted Maintenance directly by cell phone and stated the problem. Tech stated that contract Maintenance would be called and it would be a lengthy process.In the meantime; a commuting pilot in the back came up and indicated the Flight Attendant was making a bigger deal of it than what it really was. The odor wasn't increasing but was noticeable. I called the Dispatcher and relayed the issue and asked to delay the flight for 10 minutes until we could assess the issue. I mentioned we were considering taxiing out to allow the engine bleeds to run the packs and see if the odor improved. If not; we would return to the gate. I also asked him to relay the information to Maintenance.The plan was discussed with the First Officer and first FA (Flight Attendant). A final check would be made with the FA before departure to see what the conditions were. Start-up and slow taxi were made. The odor was not as noticeable in the flight deck. Called the FA and he stated he could now smell the passengers' food on the plane more than the odor. We departed for ZZZ1. After the initial descent; FA called and said the odor was noticeable again. ACARS message was sent to dispatch with ARMS Code to relay to Maintenance. All appropriate acknowledgments were made. AML entry made.Around 10;000 ft. FA called and said the smell had increased. After landing; we did not use the APU bleed for the packs. Ground air was connected and began to clear out the odor at the gate as passengers exited the aircraft.Neither the FO nor I experienced any physiological conditions from the odor. None of the flight attendants reported anything except the odor and did not indicate the passengers were experiencing any conditions. Maintenance was not observed to be at the gate.This was my final flight to maintain landing currency. The lack of regular line flying over the past several years could have been a factor. The primary causal factor was a bias towards previous experience with this particular odor and it was treated as somewhat routine.The core issue is making certain I follow the intended SOPS for fume events. The issue was downplayed by me but other resources and steps should have been followed.


Second narrative: The Captain and I returned to the plane after a 15 minute break inside the terminal in ZZZ. We discovered an odor throughout the aircraft similar to dirty socks that had not been present when we left the plane. It was determined that the station had hooked up the jetbridge ground air conditioning while we were inside and the odor was also strong in the jetbridge directly above the ground air unit. The Captain conferred with Maintenance and the flight attendants while we ran the APU to try and clear out the odor. After a short time; all parties agreed that the odor seemed to be slowly dissipating and was not a problem with the aircraft itself. We boarded and departed the gate.During the taxi out the Captain again talked to the lead Flight Attendant to confirm that the odor was dissipating and wasn't so strong as to be an issue for the comfort of the passengers. We completed the flight without further issue. The Captain did send a message to Dispatch/Maintenance enroute for someone to check the plane in ZZZ1 to see what could be done about eliminating the residual odor.


Synopsis: Air carrier flight crew reported a possible fumes event during departure and again during arrival.  The fumes were described as a 'dirty sock' odor.