Narrative:

Departed pit en route to bwi with an FAA maintenance safety inspector on my jump seat as an observer. Shortly after takeoff, we received an ECAM caution regarding an engine #1 probe fault with no further ECAM follow-up requirements. I xferred control of the aircraft to the first officer and researched this probe fault in our aircraft handbook chapter 21, to verify that this fault, while in the air, is for 'pilot awareness only,' no further crew action required. This probe fault also caused the affected engine (#1) to surge by increasing then decreasing power output, causing the aircraft to yaw due to this surge. After discussion with my first officer and the FAA observer, I determined that the surge did not warrant a return to the field (pit). The throttle lever angle donut and power limit mark were surging between 90% and 115% range with engine power trying to follow. Since these indicators are maximum limit and the power requirement was well below this level, the engine never surged more than 10-15% above or below actual requirements. This scenario sets the stage for the following event: while on a descent from approximately 16000 ft to assigned 10000 ft, we received a TA at approximately 13000 ft at 10 O'clock position. The VFR cessna was positively idented by me, my first officer and the FAA observer as climbing with a high deck angle at approximately 2-3 mi, 400 ft below us. We were in an idle descent at approximately 2500-3000 FPM descent with the #1 engine still surging at idle power. The TA turned to an RA with a climb request at approximately 300 ft vertical and 1 mi horizontal separation. This scenario calls for maximum toga power and maximum effort climb. Considering the surging engine (#1) and the potential to surge beyond 115% N1 at maximum power and the violent rolling action which could follow in a climbing right turn, I chose to continue the descent because the descent rate between us was very rapid and the target aircraft (RA) was now turning towards us which would remove him from our sight. This event was in clear VFR with the target aircraft never out of positive sight to anyone in the cockpit. At no time did ATC call out the traffic or bring it to our attention! Very shortly after the 'clear of conflict,' ATC issued a frequency change but prior to leaving I asked ATC if they were talking to this aircraft and did they see it. ATC said they saw it and were not talking to it! I told them of the RA event and continued to bwi with no further events.

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Original NASA ASRS Text

Title: FLC RECEIVES TCASII RA ALERT WHILE DSNDING.

Narrative: DEPARTED PIT ENRTE TO BWI WITH AN FAA MAINT SAFETY INSPECTOR ON MY JUMP SEAT AS AN OBSERVER. SHORTLY AFTER TKOF, WE RECEIVED AN ECAM CAUTION REGARDING AN ENG #1 PROBE FAULT WITH NO FURTHER ECAM FOLLOW-UP REQUIREMENTS. I XFERRED CTL OF THE ACFT TO THE FO AND RESEARCHED THIS PROBE FAULT IN OUR ACFT HANDBOOK CHAPTER 21, TO VERIFY THAT THIS FAULT, WHILE IN THE AIR, IS FOR 'PLT AWARENESS ONLY,' NO FURTHER CREW ACTION REQUIRED. THIS PROBE FAULT ALSO CAUSED THE AFFECTED ENG (#1) TO SURGE BY INCREASING THEN DECREASING PWR OUTPUT, CAUSING THE ACFT TO YAW DUE TO THIS SURGE. AFTER DISCUSSION WITH MY FO AND THE FAA OBSERVER, I DETERMINED THAT THE SURGE DID NOT WARRANT A RETURN TO THE FIELD (PIT). THE THROTTLE LEVER ANGLE DONUT AND PWR LIMIT MARK WERE SURGING BTWN 90% AND 115% RANGE WITH ENG PWR TRYING TO FOLLOW. SINCE THESE INDICATORS ARE MAX LIMIT AND THE PWR REQUIREMENT WAS WELL BELOW THIS LEVEL, THE ENG NEVER SURGED MORE THAN 10-15% ABOVE OR BELOW ACTUAL REQUIREMENTS. THIS SCENARIO SETS THE STAGE FOR THE FOLLOWING EVENT: WHILE ON A DSCNT FROM APPROX 16000 FT TO ASSIGNED 10000 FT, WE RECEIVED A TA AT APPROX 13000 FT AT 10 O'CLOCK POS. THE VFR CESSNA WAS POSITIVELY IDENTED BY ME, MY FO AND THE FAA OBSERVER AS CLBING WITH A HIGH DECK ANGLE AT APPROX 2-3 MI, 400 FT BELOW US. WE WERE IN AN IDLE DSCNT AT APPROX 2500-3000 FPM DSCNT WITH THE #1 ENG STILL SURGING AT IDLE PWR. THE TA TURNED TO AN RA WITH A CLB REQUEST AT APPROX 300 FT VERT AND 1 MI HORIZ SEPARATION. THIS SCENARIO CALLS FOR MAX TOGA PWR AND MAX EFFORT CLB. CONSIDERING THE SURGING ENG (#1) AND THE POTENTIAL TO SURGE BEYOND 115% N1 AT MAX PWR AND THE VIOLENT ROLLING ACTION WHICH COULD FOLLOW IN A CLBING R TURN, I CHOSE TO CONTINUE THE DSCNT BECAUSE THE DSCNT RATE BTWN US WAS VERY RAPID AND THE TARGET ACFT (RA) WAS NOW TURNING TOWARDS US WHICH WOULD REMOVE HIM FROM OUR SIGHT. THIS EVENT WAS IN CLR VFR WITH THE TARGET ACFT NEVER OUT OF POSITIVE SIGHT TO ANYONE IN THE COCKPIT. AT NO TIME DID ATC CALL OUT THE TFC OR BRING IT TO OUR ATTN! VERY SHORTLY AFTER THE 'CLR OF CONFLICT,' ATC ISSUED A FREQ CHANGE BUT PRIOR TO LEAVING I ASKED ATC IF THEY WERE TALKING TO THIS ACFT AND DID THEY SEE IT. ATC SAID THEY SAW IT AND WERE NOT TALKING TO IT! I TOLD THEM OF THE RA EVENT AND CONTINUED TO BWI WITH NO FURTHER EVENTS.

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.