During cruise at FL250, approximately 130NM from Riga near to FIR BDRY (IGORO, 562136N; 0281200E) the Captain said to First Officer that his stomach is not feeling well and went to lavatory. On the way to the lavatory he fell on the floor and fainted. Cabin crew No1 was at front station at that time and provided immediate assistance to Captain as well as called aircraft passengers for a doctor on board.
Upon considering Captain’s condition the FO made decision to return back to Riga airport. Declared emergency, and requested from ATC medical assistance as well as short radar vectors.
As the descent was commenced the Passengers were informed that an early descent was to be made and diversion to Riga due to a medical emergency. The descent, approach and landing were uneventful. The aircraft landed on RWY 36 at 21:23 hrs, after landing in about 20 min remained on runway for ambulance and passenger disembarkation and then was towed and parked on stand at Riga airport.
The First Officer had a Total flight experience of 2527 hrs which 965 hrs on aircraft DHC8-Q400
It is estimated that this serious incident was caused, when the aircraft was cruising the Commander (PIC) in duty of pilot flying became incapable of performing his duty normally by a loss of consciousness, which followed after sudden stomach upset as result of Acute Respiratory Viral Infection, Acute Gastroenterocolitis, Decompensated Diabetes and Hyperglycemia.
Concerning that the appearance of these symptoms was not predicted, it is estimated to contribute the PIC did not have any subjective symptoms before flight or under current aviation medical examinations is difficult if no subjective or objective symptoms are observed.