EMB ERJ 145 ER/LR
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 211; Flight Crew Total 1800; Flight Crew Type 486
Situational Awareness
Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Flight Crew Landed As Precaution; Flight Crew Diverted
Aircraft
[En route; we] experienced 'Smoke in the cockpit'.  We were at cruise at FL240 more than half way through our flight. There was a strange odor followed by smoke emitted from the gaspers. Once that was observed we quickly donned our O2 masks and established communication. I pulled power and immediately started slowing for a descent. [The other pilot] started the QRH and notified FA (Flight Attendant) to be seated. As [he] was performing the QRH I informed ATC that we needed to descend to 10000 ft and started the descent 2000 FPM with speed brakes deployed. Once descent was started ATC asked the reason and I stated 'Smoke in cockpit'. ATC was then told to standby. The smoke eventually dispersed and masks were removed a few minutes later once pressurization was verified good. [The other pilot] completed the QRH and diversion to closest airport was requested. Vectors were given to [the closest alternate]. We taxied to the taxiway where [Airport Rescue and Firefighting] inspected the outside of the airplane. We then followed them to the gate and deplaned normally. Communication with FA did occur and she discussed a 'haze' in the cabin but no smoke. So the cabin masks were not deployed. Smell and visible smoke. Passengers did report hearing weird unusual noises around rows 8-9.Pack 2 was MEL'd and we believe Pack 1 burnt up because there was no real airflow after the smoke and it started getting warm in the plane. Even upon shutdown you could tell the pack wasn't running because it was quiet.Masks deployed; descent initiated; QRH ran; diversion completed. ATC directed and assisted the safe descent and diversion.The crew performed all procedures appropriately and within a timely manner. One item to note is that during training there is no discussion of turning hot mic off when O2 mask is on. Because during communication with FA it was hard to communicate until we turned hot mic off.
EMB-145 flight crew member reported diverting to an alternate airport after experiencing smoke in the cockpit; probably from a malfunctioning air conditioning pack.