Narrative:

While at FL350 in IMC conditions, with no WX cells displayed on the radar and captain's radar screen displaying a spoke pattern just prior to the event, aircraft encountered moderate turbulence for approximately 3 mins, followed by severe turbulence accompanied with hail for approximately 1 min. The first officer was flying the aircraft (on autoplt). I announced/placed the mode control panel/speed monitoring system to turbulence mode. First officer's L-1 window outer pane then cracked from a hail strike. I immediately took control of the aircraft and disengaged the full flight regime autothrottle system. Entry airspeed was approximately mach .84, sat M47, tat M12 and gross weight 204.0. I disengaged the autoplt in order to maintain wings level while the first officer and flight engineer monitored the speed, engines were remaining within limits (we had turned on the engine ignition upon initial encounter of turbulence). Entry into this unknown WX was sudden and degraded rapidly. Throughout the entire event, no abrupt control movements were made, as my main concern was structural loading of the aircraft. Once clear of the WX/severe turbulence, we performed a structural damage assessment of the aircraft and performed the procedures for a cracked windshield outer pane. We slowed/configured the aircraft early in the chance of a structural/gear/ctlability issue in order to provide the additional time window to work a potential problem. The aircraft and its system were operating normally, and we landed without further event. The event was also reported to ATC. After block-in, the aircraft was noted to have radome damage and paint chips missing from the wing's upper leading edge. I believe the event would have been avoided with a normally functioning color radar as you can't avoid what you can't see. Mins prior to the severe WX encounter, my radar planned position indicator intermittently displayed spokes. I asked the first officer (as the PF) if he displayed the same pattern on his ppi, to which he responded, no. We were starting to pick up light to moderate chop in IMC conditions, and I did not want to select the alternate receiver transmitter as this type of system can take up to 1 min to paint WX after switching receiver transmitters in-flight. Being in moderate chop while in IMC, I deemed it better to have at least 1 ppi painting WX than none, while the alternate receiver transmitter pwred up. First officer's ppi was not displaying 'spokes' or any defined WX cells prior to the severe turbulence/WX encounter. The radar installed on this particular aircraft is the older generation with monochromatic ppi's without the capacity of displaying WX cell intensity information. WX encounter on this event was due to a malfunctioning radar system. However, even when this older system operates normally, it lacks the performance required for safe flight operations imho. I believe that all united states certificated turbojet (high altitude) operators should be required to use radar that displays WX cell intensity as a minimum standard (color would enhance safety even more). Example for this reasoning: departing out of an airport in the intertropical convergence zone like cali, columbia, with high terrain throughout, strict adherence must be given to the departure course in order to avoid CFIT. Since the intertropical convergence zone will always have the convective WX yr round, deviating around WX is quite routine. Cali, with its small northbound departure corridor (defined by a high terrain on both sides), leaves little room for WX avoidance. When departing here at night or in IFR conditions, having a radar system that displays a storm's intensity is essential for minimum safe flight operations and radar with color ppi's is even more of a safety enhancement. Given the fact that WX radar is primarily for complete WX avoidance, it is sometimes necessary to determine if a cell tops out at 5000 ft with light precipitation or goes to FL550 with extreme precipitation/turbulence as in the above example on a departure with high/close terrain in all quadrants. This is why I believe that acrs should not utilize these older (less capable) WX radar system. Plus, these system are usually over 30+ yrs old and more prone to malfunction just due to the component's age. Again, this WX encounter was due to a radar malfunction, but I felt this would be a good opportunity to address the issue of lacking radar specification/performance with regards to flight safety. Just as TCASII was implemented and now required in order to provide collision avoidance, industry improvements should be mandated for airborne WX radar minimum performance specifications for the type of flight operations being conducted by the acrs.

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Original NASA ASRS Text

Title: B747 FLC ENCOUNTERS SEVERE TURB WHILE AT CRUISE ALT.

Narrative: WHILE AT FL350 IN IMC CONDITIONS, WITH NO WX CELLS DISPLAYED ON THE RADAR AND CAPT'S RADAR SCREEN DISPLAYING A SPOKE PATTERN JUST PRIOR TO THE EVENT, ACFT ENCOUNTERED MODERATE TURB FOR APPROX 3 MINS, FOLLOWED BY SEVERE TURB ACCOMPANIED WITH HAIL FOR APPROX 1 MIN. THE FO WAS FLYING THE ACFT (ON AUTOPLT). I ANNOUNCED/PLACED THE MODE CTL PANEL/SPD MONITORING SYS TO TURB MODE. FO'S L-1 WINDOW OUTER PANE THEN CRACKED FROM A HAIL STRIKE. I IMMEDIATELY TOOK CTL OF THE ACFT AND DISENGAGED THE FULL FLT REGIME AUTOTHROTTLE SYS. ENTRY AIRSPD WAS APPROX MACH .84, SAT M47, TAT M12 AND GROSS WT 204.0. I DISENGAGED THE AUTOPLT IN ORDER TO MAINTAIN WINGS LEVEL WHILE THE FO AND FE MONITORED THE SPD, ENGS WERE REMAINING WITHIN LIMITS (WE HAD TURNED ON THE ENG IGNITION UPON INITIAL ENCOUNTER OF TURB). ENTRY INTO THIS UNKNOWN WX WAS SUDDEN AND DEGRADED RAPIDLY. THROUGHOUT THE ENTIRE EVENT, NO ABRUPT CTL MOVEMENTS WERE MADE, AS MY MAIN CONCERN WAS STRUCTURAL LOADING OF THE ACFT. ONCE CLR OF THE WX/SEVERE TURB, WE PERFORMED A STRUCTURAL DAMAGE ASSESSMENT OF THE ACFT AND PERFORMED THE PROCS FOR A CRACKED WINDSHIELD OUTER PANE. WE SLOWED/CONFIGURED THE ACFT EARLY IN THE CHANCE OF A STRUCTURAL/GEAR/CTLABILITY ISSUE IN ORDER TO PROVIDE THE ADDITIONAL TIME WINDOW TO WORK A POTENTIAL PROB. THE ACFT AND ITS SYS WERE OPERATING NORMALLY, AND WE LANDED WITHOUT FURTHER EVENT. THE EVENT WAS ALSO RPTED TO ATC. AFTER BLOCK-IN, THE ACFT WAS NOTED TO HAVE RADOME DAMAGE AND PAINT CHIPS MISSING FROM THE WING'S UPPER LEADING EDGE. I BELIEVE THE EVENT WOULD HAVE BEEN AVOIDED WITH A NORMALLY FUNCTIONING COLOR RADAR AS YOU CAN'T AVOID WHAT YOU CAN'T SEE. MINS PRIOR TO THE SEVERE WX ENCOUNTER, MY RADAR PLANNED POS INDICATOR INTERMITTENTLY DISPLAYED SPOKES. I ASKED THE FO (AS THE PF) IF HE DISPLAYED THE SAME PATTERN ON HIS PPI, TO WHICH HE RESPONDED, NO. WE WERE STARTING TO PICK UP LIGHT TO MODERATE CHOP IN IMC CONDITIONS, AND I DID NOT WANT TO SELECT THE ALTERNATE RECEIVER XMITTER AS THIS TYPE OF SYS CAN TAKE UP TO 1 MIN TO PAINT WX AFTER SWITCHING RECEIVER XMITTERS INFLT. BEING IN MODERATE CHOP WHILE IN IMC, I DEEMED IT BETTER TO HAVE AT LEAST 1 PPI PAINTING WX THAN NONE, WHILE THE ALTERNATE RECEIVER XMITTER PWRED UP. FO'S PPI WAS NOT DISPLAYING 'SPOKES' OR ANY DEFINED WX CELLS PRIOR TO THE SEVERE TURB/WX ENCOUNTER. THE RADAR INSTALLED ON THIS PARTICULAR ACFT IS THE OLDER GENERATION WITH MONOCHROMATIC PPI'S WITHOUT THE CAPACITY OF DISPLAYING WX CELL INTENSITY INFO. WX ENCOUNTER ON THIS EVENT WAS DUE TO A MALFUNCTIONING RADAR SYS. HOWEVER, EVEN WHEN THIS OLDER SYS OPERATES NORMALLY, IT LACKS THE PERFORMANCE REQUIRED FOR SAFE FLT OPS IMHO. I BELIEVE THAT ALL UNITED STATES CERTIFICATED TURBOJET (HIGH ALT) OPERATORS SHOULD BE REQUIRED TO USE RADAR THAT DISPLAYS WX CELL INTENSITY AS A MINIMUM STANDARD (COLOR WOULD ENHANCE SAFETY EVEN MORE). EXAMPLE FOR THIS REASONING: DEPARTING OUT OF AN ARPT IN THE INTERTROPICAL CONVERGENCE ZONE LIKE CALI, COLUMBIA, WITH HIGH TERRAIN THROUGHOUT, STRICT ADHERENCE MUST BE GIVEN TO THE DEP COURSE IN ORDER TO AVOID CFIT. SINCE THE INTERTROPICAL CONVERGENCE ZONE WILL ALWAYS HAVE THE CONVECTIVE WX YR ROUND, DEVIATING AROUND WX IS QUITE ROUTINE. CALI, WITH ITS SMALL NBOUND DEP CORRIDOR (DEFINED BY A HIGH TERRAIN ON BOTH SIDES), LEAVES LITTLE ROOM FOR WX AVOIDANCE. WHEN DEPARTING HERE AT NIGHT OR IN IFR CONDITIONS, HAVING A RADAR SYS THAT DISPLAYS A STORM'S INTENSITY IS ESSENTIAL FOR MINIMUM SAFE FLT OPS AND RADAR WITH COLOR PPI'S IS EVEN MORE OF A SAFETY ENHANCEMENT. GIVEN THE FACT THAT WX RADAR IS PRIMARILY FOR COMPLETE WX AVOIDANCE, IT IS SOMETIMES NECESSARY TO DETERMINE IF A CELL TOPS OUT AT 5000 FT WITH LIGHT PRECIP OR GOES TO FL550 WITH EXTREME PRECIP/TURB AS IN THE ABOVE EXAMPLE ON A DEP WITH HIGH/CLOSE TERRAIN IN ALL QUADRANTS. THIS IS WHY I BELIEVE THAT ACRS SHOULD NOT UTILIZE THESE OLDER (LESS CAPABLE) WX RADAR SYS. PLUS, THESE SYS ARE USUALLY OVER 30+ YRS OLD AND MORE PRONE TO MALFUNCTION JUST DUE TO THE COMPONENT'S AGE. AGAIN, THIS WX ENCOUNTER WAS DUE TO A RADAR MALFUNCTION, BUT I FELT THIS WOULD BE A GOOD OPPORTUNITY TO ADDRESS THE ISSUE OF LACKING RADAR SPEC/PERFORMANCE WITH REGARDS TO FLT SAFETY. JUST AS TCASII WAS IMPLEMENTED AND NOW REQUIRED IN ORDER TO PROVIDE COLLISION AVOIDANCE, INDUSTRY IMPROVEMENTS SHOULD BE MANDATED FOR AIRBORNE WX RADAR MINIMUM PERFORMANCE SPECS FOR THE TYPE OF FLT OPS BEING CONDUCTED BY THE ACRS.

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.