Narrative:

Flight was supposed to start using aircraft XXXA on gate ab in ZZZ but soon after boarding passengers after a 2 hour delay a mechanic notified us that we were going to have to deplane; change aircraft; and terminal due to a maintenance problem with another aircraft; XXXB. We complied and swapped into XXXB on gate bb. We quickly boarded and left the gate. While waiting in line for departure the flight attendants notify us that they and several passengers are getting a headache from a smell described as 'wet gym socks' that seems to be getting progressively stronger. We then noticed it on the flight deck and could not identify the smell. We then notified ATC; operations; and maintenance control that we were returning to the gate for an inspection. We deplaned and a mechanic boarded to see if he could locate or duplicate the smell. After about 10 minutes of troubleshooting we could not duplicate. We then boarded and closed the door only to be notified by a flight attendant that a passenger incorrectly boarded our aircraft thinking it was going to ZZZ2 not ZZZ1. So we opened the door and allowed the passenger to deplane. We corrected the passenger count and departed the gate. After a short taxi we take off for ZZZ1. Climbing through FL240 we get an EICAS message that the forward cargo door is open. We ask ATC if we can level off at FL250. We level off at FL250 and comply with the quick reference handbook which indicates that we simply have an indication problem but due to the prior unusual smell we opted to return to ZZZ. ATC then notifies us that we are going to have to hold so we declare an emergency. We notify the flight attendants and passengers that we are returning to ZZZ due to an indication problem. We get vectored for runway 27L and land. Upon arriving at the gate we deplane and have maintenance board and troubleshoot. The mechanic decides to MEL the cargo door wereupon he discovers that the cargo door had been meled in january. After verifying the cargo door is closed we reboard and depart for ZZZ1 without further incident. After switching aircraft I should have followed the SOP and properly briefed and reviewed the flight release which includes going over the mels.

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Original NASA ASRS Text

Title: An ERJ-170 departed after a delay for a foul smell but declared an emergency and returned to land because of a forward cargo door open EICAS message. The door had previously been MEL'ed but the crew missed the MEL note.

Narrative: Flight was supposed to start using aircraft XXXA on gate AB in ZZZ but soon after boarding passengers after a 2 hour delay a Mechanic notified us that we were going to have to deplane; change aircraft; and terminal due to a Maintenance problem with another aircraft; XXXB. We complied and swapped into XXXB on gate BB. We quickly boarded and left the gate. While waiting in line for departure the Flight Attendants notify us that they and several passengers are getting a headache from a smell described as 'wet gym socks' that seems to be getting progressively stronger. We then noticed it on the flight deck and could not identify the smell. We then notified ATC; Operations; and Maintenance Control that we were returning to the gate for an inspection. We deplaned and a Mechanic boarded to see if he could locate or duplicate the smell. After about 10 minutes of troubleshooting we could not duplicate. We then boarded and closed the door only to be notified by a Flight Attendant that a passenger incorrectly boarded our aircraft thinking it was going to ZZZ2 not ZZZ1. So we opened the door and allowed the passenger to deplane. We corrected the passenger count and departed the gate. After a short taxi we take off for ZZZ1. Climbing through FL240 we get an EICAS message that the forward cargo door is open. We ask ATC if we can level off at FL250. We level off at FL250 and comply with the Quick Reference Handbook which indicates that we simply have an indication problem but due to the prior unusual smell we opted to return to ZZZ. ATC then notifies us that we are going to have to hold so we declare an emergency. We notify the Flight Attendants and passengers that we are returning to ZZZ due to an indication problem. We get vectored for Runway 27L and land. Upon arriving at the gate we deplane and have Maintenance board and troubleshoot. The Mechanic decides to MEL the cargo door wereupon he discovers that the cargo door had been MELed in January. After verifying the cargo door is closed we reboard and depart for ZZZ1 without further incident. After switching aircraft I should have followed the SOP and properly briefed and reviewed the flight release which includes going over the MELs.

Data retrieved from NASA's ASRS site as of April 2012 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.