Narrative:

Approximately 10 minutes after reaching our final cruise altitude of FL250 (to comply with the operational requirements for the pack 1 MEL); myself and the captain simultaneously noticed a very unusual and strong burning smell. Within two seconds or less; the flight attendant called us and confirmed that there was smoke building in the cabin from an undeterminable source. The captain instructed her to prepare the cabin for an emergency landing. We completed our cabin fire or smoke memory items and informed ATC. Initially they gave us direct ZZZ1; but we then asked if there was a closer suitable airport. ATC replied; 'ZZZ; 12 o'clock; about forty miles'. We replied that we intended to land at ZZZ and that we would need emergency trucks/personnel standing by. As we headed direct to ZZZ and initiated an expeditious descent; we spoke with the flight attendant again to get an update and she said the smoke/smell had started to dissipate. We advised her that we were diverting to ZZZ and to inform us of any pertinent info until we configured for landing. The approach and landing into ZZZ was expedited but normal. We landed on runway 14 and exited the runway onto [the] taxiway. We removed our oxygen masks and smoke goggles and asked the fire trucks to complete an exterior inspection of the aircraft. The captain turned off both bleeds (1 & 2) as well as pack 2. It immediately started to feel like it was getting extremely warm in the cockpit. After a brief discussion; we agreed that we should evacuate the passengers out the main cabin door onto the taxiway to get them to a safe location away from the aircraft. We completed the emergency evacuation checklist and then the captain jumped out first to assist the passengers down and out while I remained behind ready with a fire extinguisher if needed. All passengers were instructed to sit first and no one appeared to have any trouble or sustain any injury. After everyone was off (including myself) and gathered in a safe location with the flight attendant and emergency responders; the captain went back to the aircraft to perform a final walk-through to ensure no one was left on board and that the batteries were selected off. The passengers were shortly afterward transported to the terminal via van/bus and the flight attendant remained with the passengers. We stayed with the aircraft until maintenance towed the aircraft to an area just outside the hangar. They determined that a bearing in the pack 2 system had failed; causing the impellor to contact/grind against the metal housing creating the burning smell and smoke. They replaced both packs. We then taxied the aircraft to the terminal/gate to begin boarding the passengers to continue to [destination].smoke and possible aircraft fire were the primary threats at hand as well as the threat of panic leading to critical errors. Multiple MEL's including the ACARS system being inoperative further complicated things as well.

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Original NASA ASRS Text

Title: EMB-145XR First Officer reported diverting to nearest suitable airport when they noticed a burning smell from a hot pack.

Narrative: Approximately 10 minutes after reaching our final cruise altitude of FL250 (to comply with the operational requirements for the PACK 1 MEL); myself and the Captain simultaneously noticed a very unusual and strong burning smell. Within two seconds or less; the flight attendant called us and confirmed that there was smoke building in the cabin from an undeterminable source. The Captain instructed her to prepare the cabin for an emergency landing. We completed our Cabin Fire or Smoke memory items and informed ATC. Initially they gave us direct ZZZ1; but we then asked if there was a closer suitable airport. ATC replied; 'ZZZ; 12 o'clock; about forty miles'. We replied that we intended to land at ZZZ and that we would need emergency trucks/personnel standing by. As we headed direct to ZZZ and initiated an expeditious descent; we spoke with the flight attendant again to get an update and she said the smoke/smell had started to dissipate. We advised her that we were diverting to ZZZ and to inform us of any pertinent info until we configured for landing. The approach and landing into ZZZ was expedited but normal. We landed on runway 14 and exited the runway onto [the] taxiway. We removed our oxygen masks and smoke goggles and asked the fire trucks to complete an exterior inspection of the aircraft. The Captain turned off both bleeds (1 & 2) as well as PACK 2. It immediately started to feel like it was getting extremely warm in the cockpit. After a brief discussion; we agreed that we should evacuate the passengers out the main cabin door onto the taxiway to get them to a safe location away from the aircraft. We completed the emergency evacuation checklist and then the Captain jumped out first to assist the passengers down and out while I remained behind ready with a fire extinguisher if needed. All passengers were instructed to sit first and no one appeared to have any trouble or sustain any injury. After everyone was off (including myself) and gathered in a safe location with the flight attendant and emergency responders; the Captain went back to the aircraft to perform a final walk-through to ensure no one was left on board and that the batteries were selected off. The passengers were shortly afterward transported to the terminal via van/bus and the flight attendant remained with the passengers. We stayed with the aircraft until maintenance towed the aircraft to an area just outside the hangar. They determined that a bearing in the PACK 2 system had failed; causing the impellor to contact/grind against the metal housing creating the burning smell and smoke. They replaced both PACKs. We then taxied the aircraft to the terminal/gate to begin boarding the passengers to continue to [destination].Smoke and possible aircraft fire were the primary threats at hand as well as the threat of panic leading to critical errors. Multiple MEL's including the ACARS system being INOP further complicated things as well.

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.