What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
(-23) Aircraft ATR-72 flight number 5465 departed Bloomington, IL enroute to st. louis at approximately 1202UTC. Approximately 10 NM out of Bloomington, IL the electrical smoke warning light illuminated and pilot declared an emergency. Aircraft returned to Bloomington, IL and landed without further incident. Maintenance personnel from st. louis performed inspections and tests but could not duplicate the malfunction on the ground. Maintenance entries were made in aircraft records and reports filed. Technical support from aircraft manufacturer was requested for system information. The system is an ionization detector system would indicate smoke or electrical/electronic component overheated condition as in a short circuit or failure from over current or excessive heat.
As the FAA filed it
(-23) AIRCRAFT ATR-72 FLIGHT NUMBER 5465 DEPARTED BLOOMINGTON, IL ENROUTE TO ST. LOUIS AT APPROXIMATELY 1202UTC. APPROXIMATELY 10 NM OUT OF BLOOMINGTON, IL THE ELECTRICAL SMOKE WARNING LIGHT ILLUMINATED AND PILOT DECLARED AN EMERGENCY. AIRCRAFT RETURNED TO BLOOMINGTON, IL AND LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE PERSONNEL FROM ST. LOUIS PERFORMED INSPECTIONS AND TESTS BUT COULD NOT DUPLICATE THE MALFUNCTION ON THE GROUND. MAINTENANCE ENTRIES WERE MADE IN AIRCRAFT RECORDS AND REPORTS FILED. TECHNICAL SUPPORT FROM AIRCRAFT MANUFACTURER WAS REQUESTED FOR SYSTEM INFORMATION. THE SYSTEM IS AN IONIZATION DETECTOR SYSTEM WOULD INDICATE SMOKE OR ELECTRICAL/ELECTRONIC COMPONENT OVERHEATED CONDITION AS IN A SHORT CIRCUIT OR FAILURE FROM OVER CURRENT OR EXCESSIVE HEAT.