Narrative:

A large line of thunderstorms were crossing the route with tops above FL400 over carps intersection on ar-3. I decided to cross circumnaving the targets so we prepare in advance. People: take your seats, fasten seat belts for turbulence. Aircraft: anti-ice system on. Penetration speed (mach .76). Approaching the line, we start a 5 NM east deviation. Abeam carps without any indication on radar the WX started to deteriorate very fast with ice, static and turbulence. Then the aircraft starts a slight shake with the airspeed decreasing continuously. We try to contact center asking for lower level with no answer. So we declare the emergency descent to keep or increase the minimum airspeed as follows: blind transmission done, squawk 7700, more deviation left of course, descending 2000 FPM. Thrust on go around. Crossing FL280 stall warning activates. We increase the rate to 4000 FPM. Crossing FL230 the airspeed start to increase, the shake disappears and the WX improves, at FL210 we level with cruise speed and thrust. Finally we contact center and continue our flight with no further problems. Conclusions: altitude capability degraded by ice build-up, adverse shear and anti-ice system.

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Original NASA ASRS Text

Title: MLG ACFT IN CRUISE ON OCEANIC AIRWAY ENCOUNTERED SEVERE WX. ICING AND TURB RESULTED IN ACFT APCHING STALL SPD WHILE FLC TRIED TO CONTACT CTLR FOR LOWER ALT, BUT WERE UNABLE. FLC DECLARED EMER IN THE BLIND. COMMENCED DSCNT AND HAD TO DSND TO FL210 BEFORE THEY WERE ABLE TO REGAIN AIRSPD.

Narrative: A LARGE LINE OF TSTMS WERE XING THE RTE WITH TOPS ABOVE FL400 OVER CARPS INTXN ON AR-3. I DECIDED TO CROSS CIRCUMNAVING THE TARGETS SO WE PREPARE IN ADVANCE. PEOPLE: TAKE YOUR SEATS, FASTEN SEAT BELTS FOR TURB. ACFT: ANTI-ICE SYS ON. PENETRATION SPD (MACH .76). APCHING THE LINE, WE START A 5 NM E DEV. ABEAM CARPS WITHOUT ANY INDICATION ON RADAR THE WX STARTED TO DETERIORATE VERY FAST WITH ICE, STATIC AND TURB. THEN THE ACFT STARTS A SLIGHT SHAKE WITH THE AIRSPD DECREASING CONTINUOUSLY. WE TRY TO CONTACT CTR ASKING FOR LOWER LEVEL WITH NO ANSWER. SO WE DECLARE THE EMER DSCNT TO KEEP OR INCREASE THE MINIMUM AIRSPD AS FOLLOWS: BLIND XMISSION DONE, SQUAWK 7700, MORE DEV L OF COURSE, DSNDING 2000 FPM. THRUST ON GAR. XING FL280 STALL WARNING ACTIVATES. WE INCREASE THE RATE TO 4000 FPM. XING FL230 THE AIRSPD START TO INCREASE, THE SHAKE DISAPPEARS AND THE WX IMPROVES, AT FL210 WE LEVEL WITH CRUISE SPD AND THRUST. FINALLY WE CONTACT CTR AND CONTINUE OUR FLT WITH NO FURTHER PROBS. CONCLUSIONS: ALT CAPABILITY DEGRADED BY ICE BUILD-UP, ADVERSE SHEAR AND ANTI-ICE SYS.

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.