|37000 Feet||Browse and search NASA's
Aviation Safety Reporting System
|Local Time Of Day||1201 To 1800|
|Locale Reference||atc facility : hvq|
|Altitude||msl bound lower : 34700|
msl bound upper : 35000
|Controlling Facilities||artcc : zid|
artcc : zdc
|Operator||general aviation : corporate|
|Make Model Name||Light Transport, Low Wing, 2 Turbojet Eng|
|Flight Phase||cruise other|
|Function||flight crew : first officer|
oversight : pic
|Qualification||pilot : atp|
pilot : cfi
|Experience||flight time last 90 days : 150|
flight time total : 15000
flight time type : 2000
|Function||flight crew : captain|
|Qualification||pilot : atp|
|Anomaly||aircraft equipment problem : less severe|
altitude deviation : undershoot
|Independent Detector||aircraft equipment other aircraft equipment : unspecified|
|Resolutory Action||none taken : anomaly accepted|
|Consequence||faa : reviewed incident with flight crew|
|Air Traffic Incident||other|
After flying 3 legs of a 5 leg trip we experienced a partial loss of our #1 air data computer. Prior to the problem on leg #4 we had been flying in heavy rain and also had quick turned our last stop. I believe the problem was caused by ice accumulation in the static system. As we were climbing through FL330 for FL350 the pilot in the left seat noticed a 200-300' difference in the altimeters. After turning off the autoplt and manually leveling off the aircraft at FL350 we switched the autoplt to the right side. After leveling off we noticed the vsi and altimeter on the left side were moving up and down 50-100', and still showing us to be about 300' low. We then descended to a lower altitude and hand flew the aircraft the last 200 mi to our destination. After descending to a lower altitude the problem seemed to correct itself. After sitting on the ground for about 40 mins (OAT and 65 degrees F) and seeing that all again looked normal, I decided to ferry the aircraft home at a lower altitude. The trip home was uneventful and everything worked normally. I don't know what could be done to correct the situation, but I do know that a good instrument scan by both pilots will help reduce the possibility of busting an altitude in this type situation.
Original NASA ASRS Text
Title: AIR DATA COMPUTER MALFUNCTION ACCOUNT MOISTURE OR ICING IN PITOT STATIC SYSTEM.
Narrative: AFTER FLYING 3 LEGS OF A 5 LEG TRIP WE EXPERIENCED A PARTIAL LOSS OF OUR #1 AIR DATA COMPUTER. PRIOR TO THE PROB ON LEG #4 WE HAD BEEN FLYING IN HEAVY RAIN AND ALSO HAD QUICK TURNED OUR LAST STOP. I BELIEVE THE PROB WAS CAUSED BY ICE ACCUMULATION IN THE STATIC SYS. AS WE WERE CLBING THROUGH FL330 FOR FL350 THE PLT IN THE LEFT SEAT NOTICED A 200-300' DIFFERENCE IN THE ALTIMETERS. AFTER TURNING OFF THE AUTOPLT AND MANUALLY LEVELING OFF THE ACFT AT FL350 WE SWITCHED THE AUTOPLT TO THE RIGHT SIDE. AFTER LEVELING OFF WE NOTICED THE VSI AND ALTIMETER ON THE LEFT SIDE WERE MOVING UP AND DOWN 50-100', AND STILL SHOWING US TO BE ABOUT 300' LOW. WE THEN DSNDED TO A LOWER ALT AND HAND FLEW THE ACFT THE LAST 200 MI TO OUR DEST. AFTER DSNDING TO A LOWER ALT THE PROB SEEMED TO CORRECT ITSELF. AFTER SITTING ON THE GND FOR ABOUT 40 MINS (OAT AND 65 DEGS F) AND SEEING THAT ALL AGAIN LOOKED NORMAL, I DECIDED TO FERRY THE ACFT HOME AT A LOWER ALT. THE TRIP HOME WAS UNEVENTFUL AND EVERYTHING WORKED NORMALLY. I DON'T KNOW WHAT COULD BE DONE TO CORRECT THE SITUATION, BUT I DO KNOW THAT A GOOD INSTRUMENT SCAN BY BOTH PLTS WILL HELP REDUCE THE POSSIBILITY OF BUSTING AN ALT IN THIS TYPE SITUATION.
Data retrieved from NASA's ASRS site as of August 2007 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.