Narrative:

During departure; we experienced a loss of an air data computer (air data computer) at the time of gear retraction. We lost all flight director command bar information and the mach trim comparator light came on. While trying to hand fly a very short heading and turn we had 3 different airspeed indications and 3 different altitude readouts. Upon reaching the initial altitude for the departure of 1500 feet; one altimeter read 1200 feet; another read 1600 feet and the third altimeter was about 1300 feet. We had the captain's airspeed indicators approaching 250 the copilot's reading 180 and the standby reading 200. ATC asked us to verify our altitude which we stated after correcting back to 1500 feet. We were preoccupied running the abnormal checklist and unable to complete any items that could get us our information back on the routing. We evaluated the ground speed readouts and determined that the captain's reading was correct based upon a quickly run E6B manual computer. Continuing during the climbout we had various airspeed readings. The controller cleared us to 10 thousand feet and by this time we had re-engaged our command bars; engaged the mach trim and had almost everything under control except figuring out which airspeed was still off. We had run the entire abnormal checklist for a comparator failure; even switching to the alternate static sources on the copilot side with no change in the indication on his panel. Out of 15000 feet the comparator light went out; both air data computer computers came up to operation status and the rest of the flight was normal until our downwind leg on arrival at which time when we lowered the flaps the mach trim light went out and the flight director command bars failed again. Upon landing we discovered the cause of this situation. The 4 inch door which covers the manual nose door release handle and contains the O2 gauge had come open. This disruption in airflow in front of the copilot pitot tube and the rose mount probe had caused a disagreement in the two air data computer systems and thus dropped off the entire system. Rendering a complete set of instruments to be unreliable. We can only speculate as to the cause due to distractions that the copilot experienced during the preflight. It is my responsibility; we're both captains and preflight for each other. Did the door close in flight to cause all indication to return to normal; and then with a change in the pitch attitude during the down-wind leg cause the door to open again and disrupt the airflow again where by losing the command bars; effecting the altimeters and airspeed again?

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Original NASA ASRS Text

Title: Challenger 600 flight crew reported experiencing multiple instrument malfunctions which lead to an altitude deviation on climbout. After landing the crew discovered that an access door in front of the First Officer's pitot tube was open and disrupted airflow around the pitot tube.

Narrative: During departure; we experienced a loss of an ADC (Air Data Computer) at the time of gear retraction. We lost all Flight Director Command Bar information and the Mach Trim Comparator light came on. While trying to hand fly a very short heading and turn we had 3 different airspeed indications and 3 different altitude readouts. Upon reaching the initial altitude for the departure of 1500 feet; one altimeter read 1200 feet; another read 1600 feet and the third altimeter was about 1300 feet. We had the Captain's airspeed indicators approaching 250 the copilot's reading 180 and the standby reading 200. ATC asked us to verify our altitude which we stated after correcting back to 1500 feet. We were preoccupied running the abnormal checklist and unable to complete any items that could get us our information back on the routing. We evaluated the ground speed readouts and determined that the Captain's reading was correct based upon a quickly run E6B manual computer. Continuing during the climbout we had various airspeed readings. The controller cleared us to 10 thousand feet and by this time we had re-engaged our command bars; engaged the Mach Trim and had almost everything under control except figuring out which airspeed was still off. We had run the entire abnormal checklist for a comparator failure; even switching to the alternate static sources on the copilot side with no change in the indication on his panel. Out of 15000 feet the comparator light went out; both ADC Computers came up to operation status and the rest of the flight was normal until our downwind leg on arrival at which time when we lowered the flaps the Mach trim light went out and the flight director command bars failed again. Upon landing we discovered the cause of this situation. The 4 inch door which covers the manual nose door release handle and contains the O2 gauge had come open. This disruption in airflow in front of the copilot pitot tube and the Rose Mount Probe had caused a disagreement in the two ADC systems and thus dropped off the entire system. Rendering a complete set of instruments to be unreliable. We can only speculate as to the cause due to distractions that the copilot experienced during the preflight. It is my responsibility; we're both captains and preflight for each other. Did the door close in flight to cause all indication to return to normal; and then with a change in the pitch attitude during the down-wind leg cause the door to open again and disrupt the airflow again where by losing the command bars; effecting the altimeters and airspeed again?

Data retrieved from NASA's ASRS site 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.