On 6 March 2018, smoke was detected coming from flight deck and passenger cabin air conditioning vents of an en-route Bombardier DHC8-400. A MAYDAY was declared to ATC but the prescribed response effectively cleared the smoke and no emergency evacuation on landing was deemed necessary. The Investigation found that the smoke was caused by oil leaking into the air conditioning system due to a failed right hand engine seal. The operator subsequently began to implement a recommended engine modification and adopt a system provided by the engine manufacturer to proactively detect such oil leaks before air conditioning systems are contaminated.