B737-400 flight crew reported the aircraft failed to depressurize on the ground after arrival. The flight crew checked several times for correct actions and indications prior to attempting to open the L1 and R1 doors. When these doors would not operate; the First Officer attempted to operate the main deck cargo door; resulting in damage to the cargo door; smoke barrier door and interior of the main cargo deck.
Synopsis
B737-400 flight crew reported the aircraft failed to depressurize on the ground after arrival. The flight crew checked several times for correct actions and indications prior to attempting to open the L1 and R1 doors. When these doors would not operate; the First Officer attempted to operate the main deck cargo door; resulting in damage to the cargo door; smoke barrier door and interior of the main cargo deck.
Narrative
Aircraft X was operating earlier that morning from ZZZ1 to ZZZ2. The aircraft landed and took off with no incident or pressurization problems. Upon landing on its final flight for that day; Day 0 in ZZZ it failed to fully depressurize; causing damage to the cargo door and smoke barrier door. Aircraft was parked on the ramp with both engines shut down and APU running; the pressurization mode selector was in ground position and outflow valves were fully open. The First Officer attempted to open the L1 door and they were unable to open the L1 door. The First Officer then came back into the flight deck and verified the selector switch was in the ground position and the valves were open and the cabin altitude showed zero. They went back out to open the L1 door and were unable to open the door. The First Officer came back to the flight deck a second time to check the pressurization switch was in ground and the valves were fully open and cabin altitude showed zero. The First Officer then went to the L1 and then R1 door and attempted to open that door and was still unable to open that door. They then attempted to open the cargo door. They checked three times and all three times there was no indication of the aircraft being pressurized. When the cargo door was opened; it was then the smoked barrier door was blown off into the cargo area and the cargo door arm was sheared off. When we opened the cargo door. Aircraft did not fully depressurize. Unexpectedly; all the indications were that the plane was depressurized. If we can't open the L1 doors or R1 call Maintenance even if all indications show aircraft completely depressurized.
Second reporter narrative
Aircraft X was operated from ZZZ1 to ZZZ2. That same morning it took off and landed with no pressurization issues. Aircraft was on its final leg for the Day 0 from ZZZ2 to ZZZ. During that flight it did not show any indications of pressurization issues until we parked; even then there were indications in the flight deck that there was a problem. Airplane was parked on the ground in ZZZ; engines were shut down and APU was running. Aircraft showed indications of being fully depressurized; outflow valves fully open; pressurization mode selector was selected to ground and cabin altitude was at zero. First Officer went to open the L1 door first; they were unable to open the door; returned back to check the pressurization selector; confirmed it was in ground. First Officer went back out again to L1 door they were unable to open the door then came back into the flight deck to check the pressurization selector a second time and confirmed it was in ground and everything was reading normal; outflow valves and cabin altitude. The First Officer came back out the third time; tried the R2 door and they were not able to open the door; it was after the three attempts that they tried to open the cargo door. When they opened the cargo door; it popped off the cargo door arm and the smoke barrier door flew into the cargo area causing damage to the cargo door arm and smoke barrier door; and layers of the interior of the cabin.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.