Narrative:

Approximately 15 mins after departing on an far part 135 IFR passenger flight under day VFR conditions; the right side cowling opened in-flight at 8000 ft MSL. I immediately slowed the airplane to minimum ctlable airspeed and extended the flaps and landing gear and then declared an emergency to center and requested clearance to the nearest airport. The controller vectored me to ZZZ and I was given priority handling. After landing; I inspected the cowling and determined no mechanical irregularities or any damage from its opening in-flight. I closed and secured the cowling and called the director of operations for our air carrier and received permission to continue the originally planned flight.

Google
 

Original NASA ASRS Text

Title: BE36 PILOT REPORTS COWL OPENING IN FLIGHT WITH EMERGENCY DECLARED AND IMMEDIATE DIVERSION TO NEAREST ARPT.

Narrative: APPROX 15 MINS AFTER DEPARTING ON AN FAR PART 135 IFR PAX FLT UNDER DAY VFR CONDITIONS; THE R SIDE COWLING OPENED INFLT AT 8000 FT MSL. I IMMEDIATELY SLOWED THE AIRPLANE TO MINIMUM CTLABLE AIRSPD AND EXTENDED THE FLAPS AND LNDG GEAR AND THEN DECLARED AN EMER TO CTR AND REQUESTED CLRNC TO THE NEAREST ARPT. THE CTLR VECTORED ME TO ZZZ AND I WAS GIVEN PRIORITY HANDLING. AFTER LNDG; I INSPECTED THE COWLING AND DETERMINED NO MECHANICAL IRREGULARITIES OR ANY DAMAGE FROM ITS OPENING INFLT. I CLOSED AND SECURED THE COWLING AND CALLED THE DIRECTOR OF OPS FOR OUR ACR AND RECEIVED PERMISSION TO CONTINUE THE ORIGINALLY PLANNED FLT.

Data retrieved from NASA's ASRS site as of May 2009 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.