Date: 202106
Local time of day: 1801-2400
Location: ZZZ.ARTCC, US
Aircraft: Regional Jet 700 ER/LR (CRJ700)
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: Exterior Pax/Crew Door
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Workload; Troubleshooting; Distraction
Second reporter function: Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Person Flight Attendant; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Returned To Departure Airport; Flight Crew Landed As Precaution; Flight Crew Overcame Equipment Problem; General Flight Cancelled / Delayed
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Climbing on the SID the forward Flight Attendant called the flight deck about noise coming from the main cabin door. We verified that the doors indications were all closed. No pressurization abnormalities were noted with the CPAM system. The noise was not audible in the flight deck. Shortly after the Flight Attendant called again saying the noise was louder; at which time the CPAM and doors EICAS (Engine Indicating and Crew Alerting System) page indications were checked again. Pilot Monitoring advised the Flight Attendant to verify all door securing pins were in the green position and to try and detect if air was passing through. During this time ATC amended our climb instructions from 37;000 feet to level at 32;000 feet for traffic. When the Flight Attendant called again she said she felt air coming from the right side of the door.At this point the noise was audible through the flight deck door and inter-phone rapidly increasing in volume. We then donned our oxygen masks and decided a descent was immediately required. Pilot Monitoring advised ATC that we were beginning a descent. Upon completion of the emergency descent and at a safe altitude; Pilot Flying gave aircraft control to Pilot Monitoring. At this time an announcement was given for a precautionary landing. The Pilot Flying began setting the aircraft up for a return to ZZZ; via straight in. The approach and landing phase was conducted in accordance with normal operations and checklist procedures resulting in a standard landing and taxi to the gate. Once at the gate; the Flight Attendant had difficulty opening the MCD (Main Cabin Door). This was in addition to difficulty experienced closing the MCD for departure. Both Flight Attendants reported hearing a loud pop prior to the sharp increase in sound from the MCD in flight.The risk was a complete and rapid; possibly explosive decompression of the aircraft. Suggest extra vigilance in verifying the airworthiness of MCD seals.


Second narrative: As were climbing after departing ZZZ; our Forward Flight Attendant called the flight deck advising us that she was concerned about a loud noise coming from the main cabin door. We verified that the door was secured and all systems reported normal. We continued our climbout. She then called back and said it was getting progressively and rapidly louder and she can feel air coming from the right side. Systems were still normal. After being given an amended altitude of 32;000 [feet] from a previous altitude of 37;000 [feet]; we were cleared higher. It was at this time we heard the sound from the main cabin door through our flight deck. It was very rapidly getting worse. As a crew; concerned about pressurization issues; we immediately decided to initiate a descent. We donned our oxygen masks as a safety measure. During the descent; all systems still reported normal. However; the issue with the door was still evident. Once the descent was completed and we were at a safe altitude; as pilot flying; I handed controls to the pilot monitoring.I stated that this would be a precautionary landing and to prepare the cabin. I also made my passenger announcement. We then set the aircraft up for a return to ZZZ. The return and landing at ZZZ was completed under normal procedures and checklists. We returned to the gate as planned. After talking with the flights attendants upon landing; they reported that just prior to the sound becoming very loud they heard a 'pop' further exacerbating the issue. It should also be noted that there was trouble closing the main cabin door prior to departure. There was also trouble opening the door once we arrived at the gate. Cause MCD (Main Cabin Door) seal.


Synopsis: CRJ-700 flight crew reported they returned to their departure airport when they heard air passing through the Main Cabin Door and the Flight Attendant reported air was passing through the door. The flight landed safely and they discovered the Main Cabin Door seals failed.