Incident Description
On 29 September 2019, a Boeing 737-800 (registration SP-ENL) departed from Madrid-Barajas Airport (LEMD). Shortly after takeoff, at approximately 2,000 feet, the cabin crew (CC1 and CC4) heard a loud hissing sound coming from the forward galley and noticed a rapid drop in temperature. They informed the captain, who did not observe any door warning indications. During the climb, the crew found that the aircraft could not be pressurized regardless of the mode selected. The climb was stopped at Flight Level 100, and the crew performed the "AUTO FAIL or Unscheduled Pressurization Change" procedure. The captain decided to return to LEMD.
After landing, CC1 observed a large gap at the left forward (1L) door. The door was closed and the handle was in the horizontal position. Mechanics who arrived determined that the door had been improperly closed. Prior to departure, no ground personnel had reported any issue with the door. CC1 stated that after closing and arming the door, no gap was visible. Due to the improper positioning of the door, CC1 was unable to open it independently and had to request assistance from the pilot. After opening, mechanics performed a visual inspection, which revealed no abnormalities. The door was then closed again and a cabin pressurization test was conducted, which yielded a positive result.
Investigation Findings
The investigation did not establish a definitive cause for the incident. It was noted that the door was improperly closed, leading to a gap and pressurization loss. The absence of a door warning indication was attributed to the fact that the door closure sensor is installed only on the right side of the door frame.
Contributing Circumstances
A possible contributing circumstance was the presence of a foreign object that may have caused improper locking of the door. After takeoff, the depressurization could have sucked the object out of the aircraft, which would explain why it was not found during the inspection by mechanics at LEMD.
Preventive and Corrective Actions
The operator proposed the following preventive measures:
- In the next revision of the Cabin Crew Manual, add a point in the section on closing doors from the inside about checking the door frame and floor (especially around metal handles) to ensure they are free of debris or items that could be pinched.
- Publish information about the incident and its circumstances in an "Operations Bulletin."
- Publish information about the incident and its circumstances in a "Flight Safety Bulletin."
No additional safety recommendations were formulated by the investigation commission.