Narrative:

During this oceanic flight we noted several anomalies of the installed rockwell collins multi-scan weather radar unit. There was no indication of an internal error of the weather radar unit and it is my opinion that this unit is representative of the operation of other rockwell collins multi-scan radar units installed on this fleet.1.) during the initial hours of the flight which was conducted in daylight hours in clear air; the radar indicated a normal display which showed no radar returns. As the flight continued into an area of lower level convective activity there was appropriate display of echo returns. Our flight then entered an area of greater convective activity and with the radar in auto mode it began to display several green isolated cells approximately 80-90 miles in front of us. We continued to monitor the horizon and did not see any sign of convective activity in front of us. For 15 to 20 minutes the same size and intensity 'phantom cell' remained displayed at our 12 o'clock with the radar in the auto mode.2.) later in the flight; with the radar set to auto we had cells which did move toward the airplane as we progressed. However; a look out the window in clear air reveled no convective activity that could be associated with what we were seeing on the radar display. If we were in IMC conditions or at night we would be compelled to deviate around these 'non-existent' cells.3.) as the flight continued we entered a moonless night approaching the equator. While level at FL360 with the radar in auto mode and no echo's displayed within 80nm's of the airplane we entered the tops of visually unseen clouds and the flight went from smooth to 30 seconds of violently strong moderate turbulence with the airplane altitude alert going off as the airplane abruptly gained 300 feet of altitude. This is exactly the type of weather phenomena that this radar unit is designed to 'see' due to the extensive use of geographic weather correlation and the gain plus features of the multi-scan radar. Clearly neither the radar nor the two of us on the flight deck did not 'see' this coming.4.) another separate issue with this radar is the inconsistency of operation. During the flight in an attempt to monitor the radar operation I selected the map mode of operation and tilted the antenna down 11 degrees. This resulted in only the right 90 degrees of the ground return arc display being show; there was no ground return display on the left half of the arc. Then we repeated these same radar settings and we were able to correctly see the full 180 degree arc of the ground return. What is causing this?each of these issue is concerning to me because there is nothing in the flight manual; training handouts or pilot bulletins that address these issues. In speaking with crews on the line; the vast majority of pilots know that this radar is a problem. This radar is simply not able to be consistently relied upon and if these issues are not addressed it will only be a matter of time before we hurt someone badly as a result of entering weather that should have been avoided.

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Original NASA ASRS Text

Title: A Captain reported Rockwell Collins MultiScan weather radar unit weather and ground mapping performance inconsistencies.

Narrative: During this oceanic flight we noted several anomalies of the installed Rockwell Collins Multi-Scan weather radar unit. There was no indication of an internal error of the weather radar unit and it is my opinion that this unit is representative of the operation of other Rockwell Collins Multi-Scan radar units installed on this fleet.1.) During the initial hours of the flight which was conducted in daylight hours in clear air; the radar indicated a normal display which showed no radar returns. As the flight continued into an area of lower level convective activity there was appropriate display of echo returns. Our flight then entered an area of greater convective activity and with the radar in auto mode it began to display several green isolated cells approximately 80-90 miles in front of us. We continued to monitor the horizon and did not see any sign of convective activity in front of us. For 15 to 20 minutes the same size and intensity 'phantom cell' remained displayed at our 12 o'clock with the radar in the auto mode.2.) Later in the flight; with the radar set to auto we had cells which did move toward the airplane as we progressed. However; a look out the window in clear air reveled no convective activity that could be associated with what we were seeing on the radar display. If we were in IMC conditions or at night we would be compelled to deviate around these 'non-existent' cells.3.) As the flight continued we entered a moonless night approaching the equator. While level at FL360 with the radar in auto mode and no echo's displayed within 80nm's of the airplane we entered the tops of visually unseen clouds and the flight went from smooth to 30 seconds of violently strong moderate turbulence with the airplane altitude alert going off as the airplane abruptly gained 300 feet of altitude. This is exactly the type of weather phenomena that this radar unit is designed to 'see' due to the extensive use of Geographic Weather Correlation and the Gain PLUS features of the Multi-Scan radar. Clearly neither the radar nor the two of us on the flight deck did not 'see' this coming.4.) Another separate issue with this radar is the inconsistency of operation. During the flight in an attempt to monitor the radar operation I selected the MAP mode of operation and tilted the antenna down 11 degrees. This resulted in only the right 90 degrees of the ground return arc display being show; there was no ground return display on the left half of the arc. Then we repeated these same radar settings and we were able to correctly see the full 180 degree arc of the ground return. What is causing this?Each of these issue is concerning to me because there is nothing in the flight manual; training handouts or pilot bulletins that address these issues. In speaking with crews on the line; the vast majority of pilots know that this radar is a problem. This radar is simply not able to be consistently relied upon and if these issues are not addressed it will only be a matter of time before we hurt someone badly as a result of entering weather that should have been avoided.

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.