Narrative:

Navigating INS dir to fam VOR from east of buffi. A line of thunderstorms were indicated on the WX radar in the msy area in a southwest to northeast line. Detoured to a north heading to pass over the east end of line. After passing over line, with no echos on the WX radar, encountered moderate chop/light turbulence. Requested lower altitude. Clrd to 33000', then to 31000', 28000', 14000' and 10000'. Out of 34500-34000', we encountered severe turbulence with large variations in airspeed and altitude. Captain's airspeed indicator fluctuating between 150-350 KTS 2, 3 times during des. First officer's varied also, but 180 degrees out of phase with captain's. Observed V/south pegged 6000' down once. I was unable to attempt a level off prior to reaching 28000-30000' with the indications I was receiving from my flight instruments. Entire des in IFR conditions. I did level off at 28000', but was still encountering moderate chop, so continued to 18000' which was smooth. Was in constant communication with hou center during this time. Broke out into the clear soon after level off assessed situation. No structural, personnel or passenger injury was evident, so ascended back to 37000' crs altitude and continued to destination. Supplemental information from acn 81603: the captain elected to fly on the dir routing as no returns were along this path and only slight course changes were needed to fly between the scattered areas. There were no contours and no dappler returns. As the airplane approached the area of rain, the captain turned on the fasten seatbelt sign and the second officer made an announcement. The air was smooth with occasional light chop. The radar showed 2 small areas of light rain using the 40 mi range and 3.50 degree nd. The one left was 12 mi west, the one east was 10 mi east. Another yet smaller area appeared at 12 O'clock and 18-20 mi. As the turbulence became steady and at moderate intensity the captain requested a lower altitude. ATC indicated a traffic conflict ahead and would call back. The turbulence continued and the captain requested heading information from the first officer. Again a slight left turn, about 10 degrees, was initiated. Suddenly the airspeed indicators fell to 160K, first officer mach below .70 with a loss of 1000' in altitude. Immediately, the first officer transmitted 'heavy, severe turbulence, we're coming down.' ATC issued des clearance to FL310. The captain lowered the nose to 8-10 degrees nose down in an attempt to regain airspeed. The ivsi pegged at 6000 FPM down, the first officer airspeed at 160K, but then the captain airspeed went to the barber's pole. With the nose attitude still at 8 degrees nose down and increasing wind noise, the first officer pulled the power to idle. The captain's airspeed indicated an airspeed condition the first officer indicated below 160K turbulence and downdrafts still a factor. A lower altitude was requested. ATC assigned FL240. The captain attempted to reduce the rate of des and airspeed at around 28000'. First officer airspeed returned to normal and an overspd warning sounded. At slightly below FL240 the first officer requested still lower and received clearance to FL180 and at 21000-22000' the ivsi stabilized at 1000 FPM down, airspeed at 320K. As reports from the cabin came in, it was apparent the galleys had emptied and everyone was upset, but no one was injured. All systems were normal and the airplane was flying and responding normally. There had been some G loading on the airplane during the des, but not to the extent any crewmember felt the integrity of the airplane was damaged. Supplemental information from acn 81666: a plane flying behind us told ATC that he encountered heavy (may have said severe) turbulence and had no warning of it on his radar. Callback conversation revealed the following: reporter stated that although on instruments, according to the radar, they were past the storm front line, and as stated in narrative, no storms within 15 mi at the very closest. He did state on that day there was a jet stream to the south of msy over the gulf and another to the north over the mem area and strong winds in the immediate area. But, no real knowledge as to whether these could have been the cause. Stated was able to keep wings level with no trouble, but that no way to stop the rapid airspeed fluctuation. Afterincident he inquired of company personnel why the difference in the 2 indicated airspds. No one could give real answer to cause except to surmise may have been enough yaw to cause large pressure differences on the static ports. The company did take aircraft out of service for inspection later because of request from FAA which apparently initiated by an FAA maintenance inspector who had been riding in the coach section of aircraft but never made himself known to PIC. Reporter has heard nothing from company on results of inspection so assumes nothing was found and has had no further follow-up from FAA.

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Original NASA ASRS Text

Title: ACR HVT ENCOUNTERED SEVERE TURBULENCE AND UNABLE TO MAINTAIN ALT.

Narrative: NAVIGATING INS DIR TO FAM VOR FROM E OF BUFFI. A LINE OF TSTMS WERE INDICATED ON THE WX RADAR IN THE MSY AREA IN A SW TO NE LINE. DETOURED TO A N HDG TO PASS OVER THE E END OF LINE. AFTER PASSING OVER LINE, WITH NO ECHOS ON THE WX RADAR, ENCOUNTERED MODERATE CHOP/LIGHT TURB. REQUESTED LOWER ALT. CLRD TO 33000', THEN TO 31000', 28000', 14000' AND 10000'. OUT OF 34500-34000', WE ENCOUNTERED SEVERE TURB WITH LARGE VARIATIONS IN AIRSPD AND ALT. CAPT'S AIRSPD INDICATOR FLUCTUATING BTWN 150-350 KTS 2, 3 TIMES DURING DES. F/O'S VARIED ALSO, BUT 180 DEGS OUT OF PHASE WITH CAPT'S. OBSERVED V/S PEGGED 6000' DOWN ONCE. I WAS UNABLE TO ATTEMPT A LEVEL OFF PRIOR TO REACHING 28000-30000' WITH THE INDICATIONS I WAS RECEIVING FROM MY FLT INSTRUMENTS. ENTIRE DES IN IFR CONDITIONS. I DID LEVEL OFF AT 28000', BUT WAS STILL ENCOUNTERING MODERATE CHOP, SO CONTINUED TO 18000' WHICH WAS SMOOTH. WAS IN CONSTANT COM WITH HOU CENTER DURING THIS TIME. BROKE OUT INTO THE CLEAR SOON AFTER LEVEL OFF ASSESSED SITUATION. NO STRUCTURAL, PERSONNEL OR PAX INJURY WAS EVIDENT, SO ASCENDED BACK TO 37000' CRS ALT AND CONTINUED TO DEST. SUPPLEMENTAL INFORMATION FROM ACN 81603: THE CAPT ELECTED TO FLY ON THE DIR ROUTING AS NO RETURNS WERE ALONG THIS PATH AND ONLY SLIGHT COURSE CHANGES WERE NEEDED TO FLY BTWN THE SCATTERED AREAS. THERE WERE NO CONTOURS AND NO DAPPLER RETURNS. AS THE AIRPLANE APCHED THE AREA OF RAIN, THE CAPT TURNED ON THE FASTEN SEATBELT SIGN AND THE S/O MADE AN ANNOUNCEMENT. THE AIR WAS SMOOTH WITH OCCASIONAL LIGHT CHOP. THE RADAR SHOWED 2 SMALL AREAS OF LIGHT RAIN USING THE 40 MI RANGE AND 3.50 DEG ND. THE ONE LEFT WAS 12 MI W, THE ONE E WAS 10 MI E. ANOTHER YET SMALLER AREA APPEARED AT 12 O'CLOCK AND 18-20 MI. AS THE TURB BECAME STEADY AND AT MODERATE INTENSITY THE CAPT REQUESTED A LOWER ALT. ATC INDICATED A TFC CONFLICT AHEAD AND WOULD CALL BACK. THE TURB CONTINUED AND THE CAPT REQUESTED HDG INFO FROM THE F/O. AGAIN A SLIGHT LEFT TURN, ABOUT 10 DEGS, WAS INITIATED. SUDDENLY THE AIRSPD INDICATORS FELL TO 160K, F/O MACH BELOW .70 WITH A LOSS OF 1000' IN ALT. IMMEDIATELY, THE F/O TRANSMITTED 'HEAVY, SEVERE TURB, WE'RE COMING DOWN.' ATC ISSUED DES CLRNC TO FL310. THE CAPT LOWERED THE NOSE TO 8-10 DEGS NOSE DOWN IN AN ATTEMPT TO REGAIN AIRSPD. THE IVSI PEGGED AT 6000 FPM DOWN, THE F/O AIRSPD AT 160K, BUT THEN THE CAPT AIRSPD WENT TO THE BARBER'S POLE. WITH THE NOSE ATTITUDE STILL AT 8 DEGS NOSE DOWN AND INCREASING WIND NOISE, THE F/O PULLED THE PWR TO IDLE. THE CAPT'S AIRSPD INDICATED AN AIRSPD CONDITION THE F/O INDICATED BELOW 160K TURB AND DOWNDRAFTS STILL A FACTOR. A LOWER ALT WAS REQUESTED. ATC ASSIGNED FL240. THE CAPT ATTEMPTED TO REDUCE THE RATE OF DES AND AIRSPD AT AROUND 28000'. F/O AIRSPD RETURNED TO NORMAL AND AN OVERSPD WARNING SOUNDED. AT SLIGHTLY BELOW FL240 THE FO REQUESTED STILL LOWER AND RECEIVED CLRNC TO FL180 AND AT 21000-22000' THE IVSI STABILIZED AT 1000 FPM DOWN, AIRSPD AT 320K. AS RPTS FROM THE CABIN CAME IN, IT WAS APPARENT THE GALLEYS HAD EMPTIED AND EVERYONE WAS UPSET, BUT NO ONE WAS INJURED. ALL SYSTEMS WERE NORMAL AND THE AIRPLANE WAS FLYING AND RESPONDING NORMALLY. THERE HAD BEEN SOME G LOADING ON THE AIRPLANE DURING THE DES, BUT NOT TO THE EXTENT ANY CREWMEMBER FELT THE INTEGRITY OF THE AIRPLANE WAS DAMAGED. SUPPLEMENTAL INFORMATION FROM ACN 81666: A PLANE FLYING BEHIND US TOLD ATC THAT HE ENCOUNTERED HEAVY (MAY HAVE SAID SEVERE) TURB AND HAD NO WARNING OF IT ON HIS RADAR. CALLBACK CONVERSATION REVEALED THE FOLLOWING: RPTR STATED THAT ALTHOUGH ON INSTRUMENTS, ACCORDING TO THE RADAR, THEY WERE PAST THE STORM FRONT LINE, AND AS STATED IN NARRATIVE, NO STORMS WITHIN 15 MI AT THE VERY CLOSEST. HE DID STATE ON THAT DAY THERE WAS A JET STREAM TO THE S OF MSY OVER THE GULF AND ANOTHER TO THE N OVER THE MEM AREA AND STRONG WINDS IN THE IMMEDIATE AREA. BUT, NO REAL KNOWLEDGE AS TO WHETHER THESE COULD HAVE BEEN THE CAUSE. STATED WAS ABLE TO KEEP WINGS LEVEL WITH NO TROUBLE, BUT THAT NO WAY TO STOP THE RAPID AIRSPD FLUCTUATION. AFTERINCIDENT HE INQUIRED OF COMPANY PERSONNEL WHY THE DIFFERENCE IN THE 2 INDICATED AIRSPDS. NO ONE COULD GIVE REAL ANSWER TO CAUSE EXCEPT TO SURMISE MAY HAVE BEEN ENOUGH YAW TO CAUSE LARGE PRESSURE DIFFERENCES ON THE STATIC PORTS. THE COMPANY DID TAKE ACFT OUT OF SERVICE FOR INSPECTION LATER BECAUSE OF REQUEST FROM FAA WHICH APPARENTLY INITIATED BY AN FAA MAINT INSPECTOR WHO HAD BEEN RIDING IN THE COACH SECTION OF ACFT BUT NEVER MADE HIMSELF KNOWN TO PIC. RPTR HAS HEARD NOTHING FROM COMPANY ON RESULTS OF INSPECTION SO ASSUMES NOTHING WAS FOUND AND HAS HAD NO FURTHER FOLLOW-UP FROM FAA.

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.