CL65 CREW HAD ACCESS DOOR COME OPEN INFLT.

Narrative

JUST AFTER ROTATION; A FAIRLY LOUD BUZZING AND HIGH PITCHED WHINE WERE HEARD COMING FROM THE R SIDE OF THE ACFT NOSE. NO WARNINGS OR OTHER COCKPIT INDICATIONS OCCURRED. AFTER A SHORT CREW DISCUSSION IT WAS DECIDED SAFETY DICTATED WE RETURN TO THE POINT OF DEP. WE RECEIVED ATC VECTORS FOR A VISUAL APCH. WHILE TURNING FROM BASE TO AN APPROX 20 MI FINAL ON INDICATED AIRSPD; WARNING FLAG WAS OBSERVED FOR APPROX 1 SECOND WITH A CORRESPONDING LARGE FLUCTUATION IN AIRSPD. AIRSPD THEN RETURNED TO NORMAL. (THE DOOR IS LOCATED IN FRONT OF A PITOT TUBE.) AFTER AN UNEVENTFUL LNDG AND TAXI IN; IT WAS DISCOVERED AN OXYGEN SVC DOOR HAD OPENED UP CAUSING THE NOISE. THE DOOR IS HINGED AT THE TOP AND IS SPRING-LOADED TO STAY OPEN WHEN UNLATCHED. AFTER CREW AND MECH INSPECTION; THE HINGES AND LATCHES WERE OPERATING PROPERLY. A 7 DAY SVC CHK HAD BEEN PERFORMED THE PREVIOUS NIGHT AND THIS WAS THE FIRST FLT OF THE DAY. THE MECH AND I WERE POSITIVE IT WAS CLOSED PRIOR TO TAXI. SUPPLEMENTAL INFO FROM ACN 457725: ON TKOF; OXYGEN SVC DOOR POPPED OPEN. THIS CAUSED VERY LOUD WIND NOISES IN COCKPIT AND CAUSES MALFUNCTIONS IN AIR DATA SYS BECAUSE DOOR 1) IS IN FRONT OF 1 PITOT TUBE AND ANGLE OF ATTACK INDICATOR. 2) DOOR IS NOT HINGED INTO THE SLIPSTREAM SO AIR FORCES IT OPEN. DOOR SHOULD BE ROTATED 90 DEGS AND MOVED AWAY FROM PITOT TUBES.