What was found
(CAN) FLIGHT DEPARTED, AT 1500FT CABIN AND COCKPIT HAD A STRONG SMOKE ODOUR IN THE FORM OF A WHITE POWDER COME THROUGH THE VENTS. PASSENGERS AND CREW EXPERIENCED EYE AND THROAT IRRITATION. COCKPIT CREW DONNED OXYGEN MASKS AND DECLARED A MAYDAY WITH ATC. FLIGHT RETURNED AND LANDED ON WITHOUT FURTHER INCIDENT. AIRCRAFT WAS INSPECTED BY EMERGENCY SERVICES ONCE STOPPED ON RWY. CAPTAIN DETERMINED SAFE TO CONTINUE TO GATE. RESOLUTION FOUND HEAT EXCHANGER AND AIR CYCLE MACHINE HEAVLY CONTAMINATED WITH COFFEE . BOTH REPLACED AS PER AMM 21-51-04 AND 21-51-05. FUNCTION CHK CARRIED OUT OK FOR SERVICE.