What happened
During the initial takeoff climb, the flight crew encountered smoke within both the cockpit and the passenger compartment. In response to the situation, the pilot-in-command declared an emergency and returned the aircraft to the departure airport. Upon landing, the captain ordered an emergency evacuation of all passengers and flight crew.
During the evacuation process, it was noted that two aft emergency slides failed to deploy.
The investigation
An examination of the aircraft determined that smoke and fumes had entered the cabin via the air conditioning system. This was traced back to a wash solution that remained in the left engine for longer than the permitted duration during an engine wash performed the day before the accident. During that maintenance procedure, the engine starter failed, causing the solution to remain in the engine for more than the required 20 minutes while the starter was being replaced.
Furthermore, an inspection of the aft emergency slides revealed that the installation safety pins had not been removed and were still installed.