Narrative:

I arrived at the airport with the rest of the crew to execute a flight to ZZZ. The aircraft was MEL'd for the cargo door indicator system 52-xx-xx on the flight release and was found to be documented correctly in the aircraft maintenance log by the cpt (captain) and reviewed by myself. This MEL mandates that the crew; before each flight; establish communication with a trained person outside of the aircraft to make sure the cargo compartment door is in the closed position with the handle locked and in the recess and that the trigger plate is latched (handle stowed position). Upon initial communication with the ground crew; the captain notified the ground crew of this MEL and that we would need the cargo door checked to ensure it was closed and latched correctly. When ready for push; ground crew stated that chocks were removed and aircraft was clear of FOD but did not mention cargo door. The captain asked the tug driver to please ensure that the cargo door was verified closed and latched; there was a pause for about a minute and the tug driver stated the cargo door was closed. The rest of the push back and takeoff took place normally and no other issues occurred until around an hour into cruise flight. I was the PF (pilot flying); in cruise flight at FL260 if I remember correctly; I went to the ecs (environmental control system) page on EICAS (engine indicating and crew alerting system) 2 to check on the cabin and pack output temperatures to ensure our passengers were remaining as comfortable as possible. While scanning this page; I noticed that our cabin altitude rate of change was not zero but increasing by 100 FPM which I thought odd since we were in cruise flight. I then looked at our cabin altitude which was 8;000 ft and thought this abnormally high for flight at FL260. I then brought both these indications to the captain's attention. During this short conversation with the captain; we received the cabin altitude caution message aural alert and message on EICAS. The captain stated that I would take radios and maintain aircraft controls while he pulled out QRH. He then stated that we should request 15000 ft from due to a cabin pressurization issue that we were troubleshooting but no emergency declaration at this time. The captain told me this was done to be closer to 10;000 ft should the issue get worse. I let ATC know and we were cleared down to 15;000 ft. I started the descent in vs mode with ap (autopilot) on at a rate of 2.5. I thought this was sufficient for the current situation considering cabin alt was only increasing by 100 FPM and cabin altitude was at 8;500 ft. Soon after the descent was initiated and the captain was doing the QRH I noticed the rate of change went from 100 to around 1;000 FPM and I let the captain know about this indication. Not long after; passing through around FL180 the cabin altitude warning message was displayed. We immediately reacted by donning O2 masks and establishing communication with one another. I then asked the captain if he would like to declare an emergency. He said to [request priority handling] with ATC and notify them of descent to 10;000 ft. I [requested priority handling] with ATC and requested 10;000 ft and was given the request immediately and was asked what else was needed to which I told them to standby while we worked the checklist. I adjusted the descent rate from vs 2.5 to 4.5 in order expedite to an emergency rate of descent. I deployed the flight spoilers to full; throttles at idle and allowed the airspeed to increase from about 260 to around 280 in the descent. During the descent I noticed the captain still had the QRH open to the amber cabin altitude message page and suggested that maybe we should change to the red cabin altitude message and he immediately agreed. During the descent I continued to monitor cabin altitude and the highest value I saw was around 11;300 ft. Approaching 10;000 ft I began to level the descent with vs to prevent the aircraft from going below the chosen altitude. Once at 10;000 ft the captain stated that we could remove O2 masks and we did. The captain called back to the flight attendant to check on the passengers and asked if everything was ok with the airplane. The flight attendant stated she thought we were nearing [our destination] but passengers were puzzled when they saw mountains but everyone was fine and did not notice the incident. As the aircraft leveled at 10;000 ft the captain was just finishing the immediate action items at the top of the QRH page. We had already donned masks and were at 10;000 ft so he said exchanging controls was no longer needed and he completed the rest of the checklist to where it said land at nearest suitable airport. We had a short discussion about what was best; continue to ZZZ which we had already briefed and loaded before the cabin altitude event and we were less than 30 minutes away or divert to nearest suitable and reload and brief everything. We both decided to follow exactly what the QRH stated even though it was going to be a lot more work and induce more pilot workload. We looked at the airports closest to us on the mfd (multi-function flight display) and settled on ZZZ1 because it was the closest; had [an air carrier] ground crew; and we were both familiar with the airport. I let ATC know of our intentions and they obliged with direct to the field routing and began to descend us into the terminal area. The captain had begun working the manual pressurization checklist as this was occurring and I began to pull up the ZZZ1 charts and preparing the FMS (flight management system) for the arrival. ATC gave us the ATIS which was fortunate as this would have also increased pilot workload going into the diversion airport. I was able to brief the approach as we were on an extended base vector for runway 21 and finished as we were being vectored to final. This is when we both noticed that we were both high and faster than we should be at this stage of the approach. I began to try to slow the airplane down with spoilers and brought in flaps as able but we were still high at 2;000 ft. The captain asked if I thought a go around was necessary and I agreed that was the safest course of action. He requested a go around with left traffic due to the fact we were VMC. We executed left traffic and re-intercepted the course for 21 in a much better aircraft state (speed; altitude; and configuration) and landed without further issue. Once at the gate we deplaned the aircraft and were told by ground crew they found our cargo door slightly open.my best guess at the cause is the ground crew did not in fact get the cargo door fully latched or there was a problem with the latch. This caused the cargo door to come open in flight resulting in the loss of cabin pressure and subsequent emergency and diversion. It's impossible to know for sure which is the case from my perspective.train ground crew better for situations dealing with MEL'd cargo doors and other various aircraft equipment deferrals that they have control over.

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Original NASA ASRS Text

Title: CRJ-200 First Officer reported encountered depressurization event inflight due to cargo door unlatch issue.

Narrative: I arrived at the airport with the rest of the crew to execute a flight to ZZZ. The aircraft was MEL'd for the Cargo Door Indicator system 52-XX-XX on the flight release and was found to be documented correctly in the aircraft maintenance log by the CPT (Captain) and reviewed by myself. This MEL mandates that the crew; before each flight; establish communication with a trained person outside of the aircraft to make sure the cargo compartment door is in the closed position with the handle locked and in the recess and that the trigger plate is latched (handle stowed position). Upon initial communication with the ground crew; the Captain notified the ground crew of this MEL and that we would need the cargo door checked to ensure it was closed and latched correctly. When ready for push; ground crew stated that chocks were removed and aircraft was clear of FOD but did not mention cargo door. The Captain asked the tug driver to please ensure that the cargo door was verified closed and latched; there was a pause for about a minute and the tug driver stated the cargo door was closed. The rest of the push back and takeoff took place normally and no other issues occurred until around an hour into cruise flight. I was the PF (Pilot Flying); in cruise flight at FL260 if I remember correctly; I went to the ECS (Environmental Control System) page on EICAS (Engine Indicating and Crew Alerting System) 2 to check on the cabin and pack output temperatures to ensure our passengers were remaining as comfortable as possible. While scanning this page; I noticed that our cabin altitude rate of change was not zero but increasing by 100 FPM which I thought odd since we were in cruise flight. I then looked at our cabin altitude which was 8;000 ft and thought this abnormally high for flight at FL260. I then brought both these indications to the Captain's attention. During this short conversation with the Captain; we received the CABIN ALTITUDE caution message aural alert and message on EICAS. The Captain stated that I would take radios and maintain aircraft controls while he pulled out QRH. He then stated that we should request 15000 ft from due to a cabin pressurization issue that we were troubleshooting but no emergency declaration at this time. The Captain told me this was done to be closer to 10;000 ft should the issue get worse. I let ATC know and we were cleared down to 15;000 ft. I started the descent in VS mode with AP (Autopilot) on at a rate of 2.5. I thought this was sufficient for the current situation considering cabin alt was only increasing by 100 FPM and cabin altitude was at 8;500 ft. Soon after the descent was initiated and the Captain was doing the QRH I noticed the rate of change went from 100 to around 1;000 FPM and I let the Captain know about this indication. Not long after; passing through around FL180 the CABIN ALTITUDE Warning message was displayed. We immediately reacted by donning O2 masks and establishing communication with one another. I then asked the Captain if he would like to declare an emergency. He said to [request priority handling] with ATC and notify them of descent to 10;000 ft. I [requested priority handling] with ATC and requested 10;000 ft and was given the request immediately and was asked what else was needed to which I told them to standby while we worked the checklist. I adjusted the descent rate from VS 2.5 to 4.5 in order expedite to an emergency rate of descent. I deployed the flight spoilers to full; throttles at idle and allowed the airspeed to increase from about 260 to around 280 in the descent. During the descent I noticed the Captain still had the QRH open to the Amber CABIN ALTITUDE message page and suggested that maybe we should change to the Red CABIN ALTITUDE message and he immediately agreed. During the descent I continued to monitor cabin altitude and the highest value I saw was around 11;300 ft. Approaching 10;000 ft I began to level the descent with VS to prevent the aircraft from going below the chosen altitude. Once at 10;000 ft the Captain stated that we could remove O2 masks and we did. The Captain called back to the Flight Attendant to check on the passengers and asked if everything was OK with the airplane. The Flight Attendant stated she thought we were nearing [our destination] but passengers were puzzled when they saw mountains but everyone was fine and did not notice the incident. As the aircraft leveled at 10;000 ft the Captain was just finishing the immediate action items at the top of the QRH page. We had already donned masks and were at 10;000 ft so he said exchanging controls was no longer needed and he completed the rest of the checklist to where it said land at nearest suitable airport. We had a short discussion about what was best; continue to ZZZ which we had already briefed and loaded before the cabin altitude event and we were less than 30 minutes away or divert to nearest suitable and reload and brief everything. We both decided to follow exactly what the QRH stated even though it was going to be a lot more work and induce more pilot workload. We looked at the airports closest to us on the MFD (Multi-function Flight Display) and settled on ZZZ1 because it was the closest; had [an air carrier] ground crew; and we were both familiar with the airport. I let ATC know of our intentions and they obliged with direct to the field routing and began to descend us into the terminal area. The Captain had begun working the manual pressurization checklist as this was occurring and I began to pull up the ZZZ1 charts and preparing the FMS (Flight Management System) for the arrival. ATC gave us the ATIS which was fortunate as this would have also increased pilot workload going into the diversion airport. I was able to brief the approach as we were on an extended base vector for Runway 21 and finished as we were being vectored to final. This is when we both noticed that we were both high and faster than we should be at this stage of the approach. I began to try to slow the airplane down with spoilers and brought in flaps as able but we were still high at 2;000 ft. The Captain asked if I thought a go around was necessary and I agreed that was the safest course of action. He requested a go around with left traffic due to the fact we were VMC. We executed left traffic and re-intercepted the course for 21 in a much better aircraft state (speed; altitude; and configuration) and landed without further issue. Once at the gate we deplaned the aircraft and were told by ground crew they found our cargo door slightly open.My best guess at the cause is the ground crew did not in fact get the cargo door fully latched or there was a problem with the latch. This caused the cargo door to come open in flight resulting in the loss of cabin pressure and subsequent emergency and diversion. It's impossible to know for sure which is the case from my perspective.Train ground crew better for situations dealing with MEL'd cargo doors and other various aircraft equipment deferrals that they have control over.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.