Narrative:

During level cruise, sps approach control asked us to check our altitude, as we were cleared to 10000'. They said they showed us at 9500'. We were actually level at 10000' according to all cockpit altimeters, and we notified ATC of same. Upon ground check of pitot static system and captain electric altimeters, maintenance changed our #1 (electric) altimeter. Have no idea how or why this came about. Only hope it is not going to be an ongoing occurrence in this aircraft. Flying the light transport for about 8 months now, several very strange things have occurred--not the least of which has been this altitude mode C reporting. When flown in heavy rain/ice, the reception of all communication radios are blocked out, seemingly blocked from the aircraft by a buildup of static. This aircraft is largely composite construction, and experience has shown me that the static discharge is not occurring as it should. I have also experienced several smaller altitude discrepancies in the past (100-300'), but never as large as this one today (500'). Perhaps now we will add to our list of things to always watch out for (or double check) will be the mode C readouts. The light transport is an all-EFIS, state of the art commuter aircraft, but there are several bugs that need to be worked out. Callback conversation with reporter revealed the following: all operators are having problems with the static buildup and unable to receive. The problem is scheduled to be a subject to be discussed with the manufacturer at an upcoming users conference. Apparently the static wicks are grounded to the aircraft metal frame with a thin metallic strip. There is some consideration the grounding is not sufficient. Also possibility that the composite composition does not have enough conductance to get the static build up to the frame or static wicks. Reporter stated they are able to transmit, but not receive, and the buildup of static is not as perceptible in the headsets as in other aircraft. Reporter also stated that the altitude problem was probably in the altimeter and not caused by the static build up as the altitude probably was just in clouds and in retrospect did not think much static built up at that time. Stated static buildup is very pronounced in snow and heavy rain.

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Original NASA ASRS Text

Title: NEW GENERATION ACR LTT DOES NOT DISSIPATE STATIC BUILDUP AND RECEPTION BECOMES BLOCKED. ALSO HAD ALT READOUT DISCREPANCY.

Narrative: DURING LEVEL CRUISE, SPS APCH CTL ASKED US TO CHK OUR ALT, AS WE WERE CLRED TO 10000'. THEY SAID THEY SHOWED US AT 9500'. WE WERE ACTUALLY LEVEL AT 10000' ACCORDING TO ALL COCKPIT ALTIMETERS, AND WE NOTIFIED ATC OF SAME. UPON GND CHK OF PITOT STATIC SYS AND CAPT ELECTRIC ALTIMETERS, MAINT CHANGED OUR #1 (ELECTRIC) ALTIMETER. HAVE NO IDEA HOW OR WHY THIS CAME ABOUT. ONLY HOPE IT IS NOT GOING TO BE AN ONGOING OCCURRENCE IN THIS ACFT. FLYING THE LTT FOR ABOUT 8 MONTHS NOW, SEVERAL VERY STRANGE THINGS HAVE OCCURRED--NOT THE LEAST OF WHICH HAS BEEN THIS ALT MODE C RPTING. WHEN FLOWN IN HEAVY RAIN/ICE, THE RECEPTION OF ALL COM RADIOS ARE BLOCKED OUT, SEEMINGLY BLOCKED FROM THE ACFT BY A BUILDUP OF STATIC. THIS ACFT IS LARGELY COMPOSITE CONSTRUCTION, AND EXPERIENCE HAS SHOWN ME THAT THE STATIC DISCHARGE IS NOT OCCURRING AS IT SHOULD. I HAVE ALSO EXPERIENCED SEVERAL SMALLER ALT DISCREPANCIES IN THE PAST (100-300'), BUT NEVER AS LARGE AS THIS ONE TODAY (500'). PERHAPS NOW WE WILL ADD TO OUR LIST OF THINGS TO ALWAYS WATCH OUT FOR (OR DOUBLE CHK) WILL BE THE MODE C READOUTS. THE LTT IS AN ALL-EFIS, STATE OF THE ART COMMUTER ACFT, BUT THERE ARE SEVERAL BUGS THAT NEED TO BE WORKED OUT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: ALL OPERATORS ARE HAVING PROBS WITH THE STATIC BUILDUP AND UNABLE TO RECEIVE. THE PROB IS SCHEDULED TO BE A SUBJECT TO BE DISCUSSED WITH THE MANUFACTURER AT AN UPCOMING USERS CONFERENCE. APPARENTLY THE STATIC WICKS ARE GNDED TO THE ACFT METAL FRAME WITH A THIN METALLIC STRIP. THERE IS SOME CONSIDERATION THE GNDING IS NOT SUFFICIENT. ALSO POSSIBILITY THAT THE COMPOSITE COMPOSITION DOES NOT HAVE ENOUGH CONDUCTANCE TO GET THE STATIC BUILD UP TO THE FRAME OR STATIC WICKS. RPTR STATED THEY ARE ABLE TO XMIT, BUT NOT RECEIVE, AND THE BUILDUP OF STATIC IS NOT AS PERCEPTIBLE IN THE HEADSETS AS IN OTHER ACFT. RPTR ALSO STATED THAT THE ALT PROB WAS PROBABLY IN THE ALTIMETER AND NOT CAUSED BY THE STATIC BUILD UP AS THE ALT PROBABLY WAS JUST IN CLOUDS AND IN RETROSPECT DID NOT THINK MUCH STATIC BUILT UP AT THAT TIME. STATED STATIC BUILDUP IS VERY PRONOUNCED IN SNOW AND HEAVY RAIN.

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.