Narrative:

Approximately 7:30 hours into the flight. The relief pilot was the pilot flying; while I was the pilot monitoring. The first officer was on break in the crew rest module. We were at FL410 cruising with a cost index of 60. An amber IAS illuminated on both pfd's. There was no other caution or warning lights. About 15-30 minutes later; the 'select #2 and #3 alternate fadec' light illuminated. We selected altitude 1; 2 and 3 fadec's to the alternate mode. We then started reading the 'select alternate fadec' checklist. While reading the checklist; approximately 2 minutes later; we started to get a constant stick shaker even though our pitch and power settings did not change since we selected the alternate switches. We did not finish the checklist at that time as the aircraft started to buffet. We called the first officer to come up to the cockpit as he was in the rest module. I took control of the aircraft and we declared an emergency and said that we were going to descend to FL200. While descending; the aircraft continued to buffet. The airspeed indicator gave conflicting signals -- the airspeed was boxed red; but it was within the safe area between the high and low speed stall region. The vsi showed a descent of 6000 FPM; but the altitude tape indicated a much slower rate of descent or approximately 1500 FPM. The pli was red and at the bottom of the HSI. The first officer remembers seeing his airspeed indicator at 247 knots and the stby indicator was at 250 knots. The captain airspeed indicator went blank during the descent. I instructed the first officer to finish running the checklist that we started earlier. We selected 1 fadec back into the normal mode. At approximately FL250; my screens blinked and then our displays went back to normal. I gave the aircraft control back to the relief pilot upon level off and he continued the descent. We called the company and told them that we were going to divert to ZZZZ. Since the relief pilot was in the first officer's seat I decided that it would not be prudent to do a seat swap. The relief pilot continued flying and made an uneventful landing at ZZZZ.supplemental information from acn 812972: upon entering the cockpit I became aware that the stall shaker was activated. I did not know if it was a high speed or low speed buffet at that time. I also noted on the captain's pfd that it appeared we were in a high rate of descent (approximately 6000 FPM) indicated on the vsi. I did not note the rate indicated on the altimeter. However; the captain later stated that he cross referenced the vsi and altitude; and the altitude did not seem to indicate a descent greater than 1500 ft. I also noted that the captain experienced two or three rolls of approximately 15 degrees to which he added power and recover to level flight. This was my first indication that we my be in a stall with associated buffet; but did not verbalize it at the time. I was still working out what was happening. The captain then informed us that his airspeed tape went blank during the descent. Shortly after I entered the cockpit the captain transferred aircraft control to the first officer and instructed me to run the level 2 select engine fadec altitude checklist. As I began to run this checklist I looked at the first officer's airspeed tape and saw the as abruptly change from its previous indication to indicate well in the red with a green trend line extended to the top of the tape. We rapidly accelerated out of the red min airspeed zone into the green and all buffeting and stick shaker activations ceased. We returned to normal flight. I continued through the checklist but informed the captain that all indications seems normal and asked if I should continue the checklist. He confirmed that I should and I noted that at its completion we were directed to run the airspeed loss; suspected; un-reliable checklist. I ran that and we concluded all had returned to normal with the exception of the engine 2/3 fadec which were now in altitude; non autopilot and autothrottles. I assume engine 1 was returned to fadec normal position. I estimate the duration of the eventnot including the divert and landing to have lasted less than 10 min.callback conversation with reporter revealed the following information: the reporter; who was the captain; stated that the fadecs were turned off in error. As part of the fadec checklist matrix; the question is asked about the airspeed stability. If the airspeed is unstable leave the fadecs on. Selecting fadec altitude is essentially turning them off and in this case that was probably an error. When the stall started the captain took control of the aircraft. The indications were extremely confusing and the crew is still not sure if they were in a high speed or low speed buffet. Additionally they had no external visual cues because it was a very dark moonless night with no horizon. When the first officer returned to the cockpit as this event was unfolding; he ran the fadec checklist at the captain's request and caught the error as he looked at the first officer's pfd which was operating and erratic at the time. Shortly after that the aircraft was below 25000 ft and the stall warning ceased. At that point the captain returned the aircraft to the first officer. After landing; the maintenance department reported that both air data computer's failed. They were replaced and the crew continued to its scheduled destination.

Related reports:

Google
 

Original NASA ASRS Text

Title: AN MD11 HAD DUAL FADEC FAILURE RESULTING IN A STALLED CONDITION AT FL410. AN EMERGENCY WAS DECLARED WITH A LANDING AT A NEARBY AIRPORT.

Narrative: APPROXIMATELY 7:30 HRS INTO THE FLIGHT. THE RELIEF PLT WAS THE PILOT FLYING; WHILE I WAS THE PILOT MONITORING. THE FO WAS ON BREAK IN THE CREW REST MODULE. WE WERE AT FL410 CRUISING WITH A COST INDEX OF 60. AN AMBER IAS ILLUMINATED ON BOTH PFD'S. THERE WAS NO OTHER CAUTION OR WARNING LIGHTS. ABOUT 15-30 MINUTES LATER; THE 'SELECT #2 AND #3 ALTERNATE FADEC' LIGHT ILLUMINATED. WE SELECTED ALT 1; 2 AND 3 FADEC'S TO THE ALTERNATE MODE. WE THEN STARTED READING THE 'SELECT ALTERNATE FADEC' CHECKLIST. WHILE READING THE CHECKLIST; APPROXIMATELY 2 MINUTES LATER; WE STARTED TO GET A CONSTANT STICK SHAKER EVEN THOUGH OUR PITCH AND POWER SETTINGS DID NOT CHANGE SINCE WE SELECTED THE ALTERNATE SWITCHES. WE DID NOT FINISH THE CHECKLIST AT THAT TIME AS THE AIRCRAFT STARTED TO BUFFET. WE CALLED THE FO TO COME UP TO THE COCKPIT AS HE WAS IN THE REST MODULE. I TOOK CONTROL OF THE AIRCRAFT AND WE DECLARED AN EMERGENCY AND SAID THAT WE WERE GOING TO DESCEND TO FL200. WHILE DESCENDING; THE AIRCRAFT CONTINUED TO BUFFET. THE AIRSPEED INDICATOR GAVE CONFLICTING SIGNALS -- THE AIRSPEED WAS BOXED RED; BUT IT WAS WITHIN THE SAFE AREA BETWEEN THE HIGH AND LOW SPEED STALL REGION. THE VSI SHOWED A DESCENT OF 6000 FPM; BUT THE ALTITUDE TAPE INDICATED A MUCH SLOWER RATE OF DESCENT OR APPROXIMATELY 1500 FPM. THE PLI WAS RED AND AT THE BOTTOM OF THE HSI. THE FO REMEMBERS SEEING HIS AIRSPEED INDICATOR AT 247 KNOTS AND THE STBY INDICATOR WAS AT 250 KNOTS. THE CAPT AIRSPEED INDICATOR WENT BLANK DURING THE DESCENT. I INSTRUCTED THE FO TO FINISH RUNNING THE CHECKLIST THAT WE STARTED EARLIER. WE SELECTED 1 FADEC BACK INTO THE NORMAL MODE. AT APPROXIMATELY FL250; MY SCREENS BLINKED AND THEN OUR DISPLAYS WENT BACK TO NORMAL. I GAVE THE AIRCRAFT CONTROL BACK TO THE RELIEF PLT UPON LEVEL OFF AND HE CONTINUED THE DESCENT. WE CALLED THE COMPANY AND TOLD THEM THAT WE WERE GOING TO DIVERT TO ZZZZ. SINCE THE RELIEF PLT WAS IN THE FO'S SEAT I DECIDED THAT IT WOULD NOT BE PRUDENT TO DO A SEAT SWAP. THE RELIEF PLT CONTINUED FLYING AND MADE AN UNEVENTFUL LANDING AT ZZZZ.SUPPLEMENTAL INFO FROM ACN 812972: UPON ENTERING THE COCKPIT I BECAME AWARE THAT THE STALL SHAKER WAS ACTIVATED. I DID NOT KNOW IF IT WAS A HIGH SPEED OR LOW SPEED BUFFET AT THAT TIME. I ALSO NOTED ON THE CAPTAIN'S PFD THAT IT APPEARED WE WERE IN A HIGH RATE OF DESCENT (APPROX 6000 FPM) INDICATED ON THE VSI. I DID NOT NOTE THE RATE INDICATED ON THE ALTIMETER. HOWEVER; THE CAPTAIN LATER STATED THAT HE CROSS REFERENCED THE VSI AND ALT; AND THE ALT DID NOT SEEM TO INDICATE A DESCENT GREATER THAN 1500 FT. I ALSO NOTED THAT THE CAPTAIN EXPERIENCED TWO OR THREE ROLLS OF APPROXIMATELY 15 DEGREES TO WHICH HE ADDED POWER AND RECOVER TO LEVEL FLIGHT. THIS WAS MY FIRST INDICATION THAT WE MY BE IN A STALL WITH ASSOCIATED BUFFET; BUT DID NOT VERBALIZE IT AT THE TIME. I WAS STILL WORKING OUT WHAT WAS HAPPENING. THE CAPTAIN THEN INFORMED US THAT HIS AIRSPEED TAPE WENT BLANK DURING THE DESCENT. SHORTLY AFTER I ENTERED THE COCKPIT THE CAPTAIN TRANSFERRED ACFT CONTROL TO THE FO AND INSTRUCTED ME TO RUN THE LEVEL 2 SELECT ENGINE FADEC ALT CHECKLIST. AS I BEGAN TO RUN THIS CHECKLIST I LOOKED AT THE FO'S AIRSPEED TAPE AND SAW THE AS ABRUPTLY CHANGE FROM ITS PREVIOUS INDICATION TO INDICATE WELL IN THE RED WITH A GREEN TREND LINE EXTENDED TO THE TOP OF THE TAPE. WE RAPIDLY ACCELERATED OUT OF THE RED MIN AIRSPEED ZONE INTO THE GREEN AND ALL BUFFETING AND STICK SHAKER ACTIVATIONS CEASED. WE RETURNED TO NORMAL FLIGHT. I CONTINUED THROUGH THE CHECKLIST BUT INFORMED THE CAPTAIN THAT ALL INDICATIONS SEEMS NORMAL AND ASKED IF I SHOULD CONTINUE THE CHECKLIST. HE CONFIRMED THAT I SHOULD AND I NOTED THAT AT ITS COMPLETION WE WERE DIRECTED TO RUN THE AIRSPEED LOSS; SUSPECTED; UN-RELIABLE CHECKLIST. I RAN THAT AND WE CONCLUDED ALL HAD RETURNED TO NORMAL WITH THE EXCEPTION OF THE ENGINE 2/3 FADEC WHICH WERE NOW IN ALT; NON AUTOPILOT AND AUTOTHROTTLES. I ASSUME ENGINE 1 WAS RETURNED TO FADEC NORMAL POSITION. I ESTIMATE THE DURATION OF THE EVENTNOT INCLUDING THE DIVERT AND LANDING TO HAVE LASTED LESS THAN 10 MIN.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REPORTER; WHO WAS THE CAPTAIN; STATED THAT THE FADECS WERE TURNED OFF IN ERROR. AS PART OF THE FADEC CHECKLIST MATRIX; THE QUESTION IS ASKED ABOUT THE AIRSPEED STABILITY. IF THE AIRSPEED IS UNSTABLE LEAVE THE FADECS ON. SELECTING FADEC ALT IS ESSENTIALLY TURNING THEM OFF AND IN THIS CASE THAT WAS PROBABLY AN ERROR. WHEN THE STALL STARTED THE CAPTAIN TOOK CONTROL OF THE AIRCRAFT. THE INDICATIONS WERE EXTREMELY CONFUSING AND THE CREW IS STILL NOT SURE IF THEY WERE IN A HIGH SPEED OR LOW SPEED BUFFET. ADDITIONALLY THEY HAD NO EXTERNAL VISUAL CUES BECAUSE IT WAS A VERY DARK MOONLESS NIGHT WITH NO HORIZON. WHEN THE FO RETURNED TO THE COCKPIT AS THIS EVENT WAS UNFOLDING; HE RAN THE FADEC CHECKLIST AT THE CAPTAIN'S REQUEST AND CAUGHT THE ERROR AS HE LOOKED AT THE FO'S PFD WHICH WAS OPERATING AND ERRATIC AT THE TIME. SHORTLY AFTER THAT THE AIRCRAFT WAS BELOW 25000 FT AND THE STALL WARNING CEASED. AT THAT POINT THE CAPTAIN RETURNED THE AIRCRAFT TO THE FO. AFTER LANDING; THE MAINTENANCE DEPARTMENT REPORTED THAT BOTH ADC'S FAILED. THEY WERE REPLACED AND THE CREW CONTINUED TO ITS SCHEDULED DESTINATION.

Data retrieved from NASA's ASRS site as of May 2009 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.