Narrative:

Departure was delayed from rio de janeiro due to thunderstorms. After departure resumed, we taxied into position on runway 15 for takeoff. Pilots turned on radar to check WX. I, the flight engineer, was unable to see radar screens due to the aircraft design, but did point out lightning straight off runway, maybe 3-5 mi out. Pilots did not see lightning with head down for radar. Captain said there were no 'rocks' on display. I said there was a 'rock' (thunderstorm) ahead though. Captain said there was only light rain to the left which was our departure route. Unfortunately, I never made sure whether the radar displayed the thunderstorm I saw visually. This would have shown radar to be faulty. Rather, we departed and made our left turn into more thunderstorms and not rain. Over marica VOR, after taking 2 lightning strikes, we were approaching 12000 ft when our airspeed fell from 275 KT to 220 KTS. Still using flaps 1 to help climb. During recovery, we descended to almost 10000 MSL just north of marica VOR (not yet to porto) when the GPWS went off with repetitions of 'too low, terrain.' maximum power was applied with pitch to almost 20 degree nose up. The copilot called 600 ft on radar altimeter before GPWS stopped. The highest elevation in that area is 3200 ft, but our altimeters showed above 1000 ft. Did the lightning cause the GPWS? Was it a heavy concentration of hail and or rain? Maybe super low pressure from thunderstorms? Although I feel now it was a false alarm, it certainly felt real, too real, at the time. Moral of the story: don't allow your departure decision to be rushed in the vicinity of thunderstorms. I personally will shut down engine rather than allow my passenger and self into a similar situation.

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Original NASA ASRS Text

Title: ACR WDB ACFT CLBED IN THUNDERSTORM WX DURING DEP AND EXPERIENCED A DOWNDRAFT WINDSHEAR AND AN APPARENT FALSE GPWS WARNING WHICH RESULTED IN LOSS OF ALT AND THEN A HIGH PITCH-UP ATTITUDE AND FULL PWR TO SILENCE THE GPWS.

Narrative: DEP WAS DELAYED FROM RIO DE JANEIRO DUE TO TSTMS. AFTER DEP RESUMED, WE TAXIED INTO POS ON RWY 15 FOR TKOF. PLTS TURNED ON RADAR TO CHK WX. I, THE FE, WAS UNABLE TO SEE RADAR SCREENS DUE TO THE ACFT DESIGN, BUT DID POINT OUT LIGHTNING STRAIGHT OFF RWY, MAYBE 3-5 MI OUT. PLTS DID NOT SEE LIGHTNING WITH HEAD DOWN FOR RADAR. CAPT SAID THERE WERE NO 'ROCKS' ON DISPLAY. I SAID THERE WAS A 'ROCK' (TSTM) AHEAD THOUGH. CAPT SAID THERE WAS ONLY LIGHT RAIN TO THE L WHICH WAS OUR DEP RTE. UNFORTUNATELY, I NEVER MADE SURE WHETHER THE RADAR DISPLAYED THE TSTM I SAW VISUALLY. THIS WOULD HAVE SHOWN RADAR TO BE FAULTY. RATHER, WE DEPARTED AND MADE OUR L TURN INTO MORE TSTMS AND NOT RAIN. OVER MARICA VOR, AFTER TAKING 2 LIGHTNING STRIKES, WE WERE APCHING 12000 FT WHEN OUR AIRSPD FELL FROM 275 KT TO 220 KTS. STILL USING FLAPS 1 TO HELP CLB. DURING RECOVERY, WE DSNDED TO ALMOST 10000 MSL JUST N OF MARICA VOR (NOT YET TO PORTO) WHEN THE GPWS WENT OFF WITH REPETITIONS OF 'TOO LOW, TERRAIN.' MAX PWR WAS APPLIED WITH PITCH TO ALMOST 20 DEG NOSE UP. THE COPLT CALLED 600 FT ON RADAR ALTIMETER BEFORE GPWS STOPPED. THE HIGHEST ELEVATION IN THAT AREA IS 3200 FT, BUT OUR ALTIMETERS SHOWED ABOVE 1000 FT. DID THE LIGHTNING CAUSE THE GPWS? WAS IT A HEAVY CONCENTRATION OF HAIL AND OR RAIN? MAYBE SUPER LOW PRESSURE FROM TSTMS? ALTHOUGH I FEEL NOW IT WAS A FALSE ALARM, IT CERTAINLY FELT REAL, TOO REAL, AT THE TIME. MORAL OF THE STORY: DON'T ALLOW YOUR DEP DECISION TO BE RUSHED IN THE VICINITY OF TSTMS. I PERSONALLY WILL SHUT DOWN ENG RATHER THAN ALLOW MY PAX AND SELF INTO A SIMILAR SIT.

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.