Date: 201912
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: IMC
Aircraft: A320
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Second reporter function: Pilot Not Flying; First Officer
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 Attendant; Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Taxiing out from ZZZ; First Officer noticed a faint odor. We discussed it and both agreed it was probably residue odor from starting the engines. After takeoff and climbing through the teens; my First Officer noticed the faint odor again. I couldn't smell anything; but thought I might be able to sense it in my throat. It was then we called the flight attendants and asked them if they smelled anything; they said they thought they smelled something like a burnt nylon rope. At no time did anyone mention 'dirty socks.' We asked them if they felt it was okay to continue since we couldn't witness firsthand what a few flight attendants were experiencing. They said yes and they would keep us informed of any changes. It wasn't until after landing we were told that they were using their personal breathing apparatuses. We decided at that point to complete a fumes event form and record it In the AML. I don't have any idea if anything really happened or not. We initiated the call to the flight attendants. Not the other way around. Odor detection is very subjective per each individual. Maybe some matter of fact guidelines to remove individual opinions form the process.


Second narrative: During startup for our flight to ZZZ1; I noticed a faint musty smell once the packs were back on after engine start. I brought this to the Captain's attention; however; he didn't smell it. Thinking I might be mistaken; I didn't press the issue further and we departed for ZZZ1. During climbout the smell went away and then returned a little stronger. This time the Captain mentioned he noticed the smell; but couldn't place it. Again the musty smell seemed to dissipate; only to return a short while later. At this point; we looked through the logbook again for history. Finding none; we decided to contact Maintenance Control via Dispatch using IPad crew phone. Maintenance Control had not had any complaints on the aircraft and the APU oil was last serviced on 11/XX/19. We didn't want to startle the flight attendants but we did ask for their feedback regarding any unusual smells in the cabin. We were told there was an unusual smell; but it was more like a burning rope smell. Since we didn't have a parallel smell response from the flight attendants; we elected to continue unless things got worse. We reviewed nearby diversion airports; finding ZZZ2 and ZZZ3 nearby; we felt safe to continue. The remainder of cruise to ZZZ1 was uneventful. During descent the smell returned stronger than before and we decided to have maintenance check the aircraft and assess the smell once we arrived at the gate. We never received a call from the flight attendants regarding a change in the smell during the descent. Subsequent to the flight; we learned a jumpseating Flight Attendant reported the smell to the flight attendants during descent; but this information wasn't passed along until after arrival. Maintenance ultimately declined to release the aircraft for continued service and we were deadheaded back to ZZZ. Had we known about the Flight Attendant difficulties regarding the odor/smell; I feel more confident we would have diverted as opposed to continuing to our destination. On the flight deck; we felt the odor was manageable given it's transient nature; but felt it should be checked out by Maintenance upon our arrival in ZZZ1.


Synopsis: A320 flight crew reported an odor initiated during takeoff and continued intermittently during the entire flight. Flight attendants reported having to use personal breathing devices to destination.