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MD11 initiates uncommanded descent while at cruise at international rvsm airspace. Flight crew complies with TCAS RA in response to opposite direction traffic 1000 ft below.
| Attributes | |
| ACN | 698137 |
| Time | |
| Date | 200605 |
| Local Time Of Day | 0001 To 0600 |
| Place | |
| Locale Reference | intersection : salmi |
| State Reference | FO |
| Altitude | msl single value : 38000 |
| Environment | |
| Weather Elements | Turbulence |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : rorg.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | MD-11 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise : level |
| Flight Plan | IFR |
| Aircraft 2 | |
| Controlling Facilities | artcc : rorg.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | Commercial Fixed Wing |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise : level |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Experience | flight time last 90 days : 133 flight time total : 8000 flight time type : 700 |
| ASRS Report | 698137 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Events | |
| Anomaly | altitude deviation : excursion from assigned altitude conflict : airborne critical inflight encounter : turbulence non adherence : required legal separation other anomaly |
| Independent Detector | aircraft equipment : tcas other flight crewa other flight crewb |
| Resolutory Action | flight crew : overrode automation flight crew : regained aircraft control flight crew : took evasive action |
| Miss Distance | horizontal : 50 vertical : 800 |
| Supplementary | |
| Problem Areas | Aircraft Airspace Structure Weather |
| Primary Problem | Ambiguous |
Narrative:
Our aircraft began an uncommanded descent in moderate to severe turbulence while cruising south on B576 at FL380 approaching salmi waypoint. At the same time an aircraft was approaching salmi from the south at FL370. The first officer whose leg it was; had been monitoring the merge with this aircraft on TCAS prior to the event. Despite immediately recognizing that our aircraft was starting to descend and disengaging the autoplt; we had already achieved a rate of descent of about 1000 FPM. Within seconds we received an RA from TCAS and flight path guidance commanding a climb to avoid the converging traffic. The first officer did an excellent job of complying with TCAS but not before losing approximately 300 ft of altitude before climbing. I was able to acquire the traffic visually and determined that we were not in imminent danger of a collision; and estimate that we were already in a positive rate of climb before the merge. We continued the climb through FL380 still following TCAS guidance commands and eventually leveled off 340 ft high. We then returned to FL380 without further incident and re-engaged the autoplt. Shortly after passage; the other aircraft reported that they had also received an RA and reported deviating from their assigned altitude in compliance with TCAS commands. ATC responded by asking if there were any further problems to report. The other aircraft said no; and continued en route. We proceeded to our destination uneventfully. It is my belief that given this set of circumstances this event could not have been foreseen ahead of time nor could the PF reacted any more quickly or appropriately. We were both rested; alert; and aware of the approaching aircraft; and yet within seconds we were rudely reminded that in an rvsm environment the remarkable precision in time and space that our current technology can place us; makes any deviation a potential disaster.
Original NASA ASRS Text
Title: MD11 INITIATES UNCOMMANDED DSCNT WHILE AT CRUISE AT INTL RVSM AIRSPACE. FLT CREW COMPLIES WITH TCAS RA IN RESPONSE TO OPPOSITE DIRECTION TFC 1000 FT BELOW.
Narrative: OUR ACFT BEGAN AN UNCOMMANDED DSCNT IN MODERATE TO SEVERE TURB WHILE CRUISING S ON B576 AT FL380 APCHING SALMI WAYPOINT. AT THE SAME TIME AN ACFT WAS APCHING SALMI FROM THE S AT FL370. THE FO WHOSE LEG IT WAS; HAD BEEN MONITORING THE MERGE WITH THIS ACFT ON TCAS PRIOR TO THE EVENT. DESPITE IMMEDIATELY RECOGNIZING THAT OUR ACFT WAS STARTING TO DSND AND DISENGAGING THE AUTOPLT; WE HAD ALREADY ACHIEVED A RATE OF DSCNT OF ABOUT 1000 FPM. WITHIN SECONDS WE RECEIVED AN RA FROM TCAS AND FLT PATH GUIDANCE COMMANDING A CLB TO AVOID THE CONVERGING TFC. THE FO DID AN EXCELLENT JOB OF COMPLYING WITH TCAS BUT NOT BEFORE LOSING APPROX 300 FT OF ALT BEFORE CLBING. I WAS ABLE TO ACQUIRE THE TFC VISUALLY AND DETERMINED THAT WE WERE NOT IN IMMINENT DANGER OF A COLLISION; AND ESTIMATE THAT WE WERE ALREADY IN A POSITIVE RATE OF CLB BEFORE THE MERGE. WE CONTINUED THE CLB THROUGH FL380 STILL FOLLOWING TCAS GUIDANCE COMMANDS AND EVENTUALLY LEVELED OFF 340 FT HIGH. WE THEN RETURNED TO FL380 WITHOUT FURTHER INCIDENT AND RE-ENGAGED THE AUTOPLT. SHORTLY AFTER PASSAGE; THE OTHER ACFT RPTED THAT THEY HAD ALSO RECEIVED AN RA AND RPTED DEVIATING FROM THEIR ASSIGNED ALT IN COMPLIANCE WITH TCAS COMMANDS. ATC RESPONDED BY ASKING IF THERE WERE ANY FURTHER PROBS TO RPT. THE OTHER ACFT SAID NO; AND CONTINUED ENRTE. WE PROCEEDED TO OUR DEST UNEVENTFULLY. IT IS MY BELIEF THAT GIVEN THIS SET OF CIRCUMSTANCES THIS EVENT COULD NOT HAVE BEEN FORESEEN AHEAD OF TIME NOR COULD THE PF REACTED ANY MORE QUICKLY OR APPROPRIATELY. WE WERE BOTH RESTED; ALERT; AND AWARE OF THE APCHING ACFT; AND YET WITHIN SECONDS WE WERE RUDELY REMINDED THAT IN AN RVSM ENVIRONMENT THE REMARKABLE PRECISION IN TIME AND SPACE THAT OUR CURRENT TECHNOLOGY CAN PLACE US; MAKES ANY DEV A POTENTIAL DISASTER.
Data retrieved from NASA's ASRS site as of January 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.