Narrative:

The aircraft in use was a CL65. On departure from gsp, the altimeters were all set at 29.88, the local setting at the airport. This was noted on the before starting engines checklist. We taxied out after starting our engines and took off on runway 3. During climb out, the captain alerted me to a deviation in our altitude readouts. We had been assigned 10000 ft. My side said/indicated 9500 ft, his above 10000 ft. We then saw that the electronic barometric display on the copilot's side was indicating 28.88. I immediately initiated a leveloff followed by an expeditious descent to 10000 ft on the corrected setting of 29.88. The deviation at its greatest was 10600 ft. No conflict occurred. This is a very troubling incident. The air data reference panel that is manufactured by collins and installed has a defect. This defect, which is now becoming recognized, occurs when there is a power spike in the aircraft's electrical system, ie, engine starts, generator selections and so on. The result is that the barometric settings are thrown off by an inch or more, in all occurrences to a lower setting. This is a potentially deadly defect which was explained to me by the avionics technician as a 'mounting problem.' upon arrival at our destination we wrote up the air data reference panel which was replaced. Collins claims it is aware of this malfunction and is correcting it. This needs to be followed up and confirmed with them. Our company is checking into making a change in the checklist procedure at this time so that the altimeter is reconfirmed prior to taking the runway. Callback conversation with reporter revealed the following information: the reporter has since this incident gathered more information on the electrical interruption effects on the air data computer. He spoke to a representative from collins and another one from bombardier. He said that he was assured that there was a fix to the problem that was currently before the auths in canada and this was to be incorporated in the new aircraft during manufacture. A kit was going to be distributed to the users of older aircraft. Both representatives, according to the reporter, said that the problem had been occurring for some time, but since the phenomenon does not always occur there were delays in tracking it down. The reporter's airline has changed its procedures so that the altimeters were again checked prior to takeoff and 1000 ft prior to all leveloffs. These new checks will help, but the reporter pointed out that the type of error that he encountered, and that he further alleged was the most common, would still result in an overshoot during a climb. The reporter also said that his 1 inch lower setting error was allegedly corrected during earlier modifications during construction, but allegedly, this fix was inconsistently applied. The new fix will be applied to all aircraft. The collins representative also apparently said that part of the new fix was a remounting of the air data computer.

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Original NASA ASRS Text

Title: AN ACR CL65 FLC CLBED ABOVE THEIR ASSIGNED ALT DUE TO AN ALTIMETER SETTING ERROR. THE ALTIMETER RESET ITSELF WHEN THE ELECTRICAL SOURCE WAS CHANGED DURING ENG START ON THE GND.

Narrative: THE ACFT IN USE WAS A CL65. ON DEP FROM GSP, THE ALTIMETERS WERE ALL SET AT 29.88, THE LCL SETTING AT THE ARPT. THIS WAS NOTED ON THE BEFORE STARTING ENGS CHKLIST. WE TAXIED OUT AFTER STARTING OUR ENGS AND TOOK OFF ON RWY 3. DURING CLBOUT, THE CAPT ALERTED ME TO A DEV IN OUR ALT READOUTS. WE HAD BEEN ASSIGNED 10000 FT. MY SIDE SAID/INDICATED 9500 FT, HIS ABOVE 10000 FT. WE THEN SAW THAT THE ELECTRONIC BAROMETRIC DISPLAY ON THE COPLT'S SIDE WAS INDICATING 28.88. I IMMEDIATELY INITIATED A LEVELOFF FOLLOWED BY AN EXPEDITIOUS DSCNT TO 10000 FT ON THE CORRECTED SETTING OF 29.88. THE DEV AT ITS GREATEST WAS 10600 FT. NO CONFLICT OCCURRED. THIS IS A VERY TROUBLING INCIDENT. THE AIR DATA REF PANEL THAT IS MANUFACTURED BY COLLINS AND INSTALLED HAS A DEFECT. THIS DEFECT, WHICH IS NOW BECOMING RECOGNIZED, OCCURS WHEN THERE IS A PWR SPIKE IN THE ACFT'S ELECTRICAL SYS, IE, ENG STARTS, GENERATOR SELECTIONS AND SO ON. THE RESULT IS THAT THE BAROMETRIC SETTINGS ARE THROWN OFF BY AN INCH OR MORE, IN ALL OCCURRENCES TO A LOWER SETTING. THIS IS A POTENTIALLY DEADLY DEFECT WHICH WAS EXPLAINED TO ME BY THE AVIONICS TECHNICIAN AS A 'MOUNTING PROB.' UPON ARR AT OUR DEST WE WROTE UP THE AIR DATA REF PANEL WHICH WAS REPLACED. COLLINS CLAIMS IT IS AWARE OF THIS MALFUNCTION AND IS CORRECTING IT. THIS NEEDS TO BE FOLLOWED UP AND CONFIRMED WITH THEM. OUR COMPANY IS CHKING INTO MAKING A CHANGE IN THE CHKLIST PROC AT THIS TIME SO THAT THE ALTIMETER IS RECONFIRMED PRIOR TO TAKING THE RWY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR HAS SINCE THIS INCIDENT GATHERED MORE INFO ON THE ELECTRICAL INTERRUPTION EFFECTS ON THE AIR DATA COMPUTER. HE SPOKE TO A REPRESENTATIVE FROM COLLINS AND ANOTHER ONE FROM BOMBARDIER. HE SAID THAT HE WAS ASSURED THAT THERE WAS A FIX TO THE PROB THAT WAS CURRENTLY BEFORE THE AUTHS IN CANADA AND THIS WAS TO BE INCORPORATED IN THE NEW ACFT DURING MANUFACTURE. A KIT WAS GOING TO BE DISTRIBUTED TO THE USERS OF OLDER ACFT. BOTH REPRESENTATIVES, ACCORDING TO THE RPTR, SAID THAT THE PROB HAD BEEN OCCURRING FOR SOME TIME, BUT SINCE THE PHENOMENON DOES NOT ALWAYS OCCUR THERE WERE DELAYS IN TRACKING IT DOWN. THE RPTR'S AIRLINE HAS CHANGED ITS PROCS SO THAT THE ALTIMETERS WERE AGAIN CHKED PRIOR TO TKOF AND 1000 FT PRIOR TO ALL LEVELOFFS. THESE NEW CHKS WILL HELP, BUT THE RPTR POINTED OUT THAT THE TYPE OF ERROR THAT HE ENCOUNTERED, AND THAT HE FURTHER ALLEGED WAS THE MOST COMMON, WOULD STILL RESULT IN AN OVERSHOOT DURING A CLB. THE RPTR ALSO SAID THAT HIS 1 INCH LOWER SETTING ERROR WAS ALLEGEDLY CORRECTED DURING EARLIER MODIFICATIONS DURING CONSTRUCTION, BUT ALLEGEDLY, THIS FIX WAS INCONSISTENTLY APPLIED. THE NEW FIX WILL BE APPLIED TO ALL ACFT. THE COLLINS REPRESENTATIVE ALSO APPARENTLY SAID THAT PART OF THE NEW FIX WAS A REMOUNTING OF THE AIR DATA COMPUTER.

Data retrieved from NASA's ASRS site as of July 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.