Narrative:

Due to the turbulent flight conditions at the higher altitudes, it was discussed and planned that we should consider FL280 for our return leg to sfo and therefore plan on fuel for the lower altitude and possible engine anti-ice. Minimum dispatch fuel departing gdl was 29.2K pounds and we departed with 31.2K pounds. Field conditions departing gdl were clear, wind calm, temperature 20 degrees C, runway 28 and night conditions. During climb out of gdl and initial cruise flight conditions were clear with the same occasional light chop/light turbulence after leveloff at FL280. Again the reports at the higher altitudes were continuous light to moderate turbulence as reported by other aircraft and central mazatlan (center), therefore, we elected to remain at FL280. After passing mzt, flight conditions became similar as those we encountered sbound, with us in the tops of thin clouds and then in the clear with the periods in the clouds of shorter duration and the periods in the clear of longer duration than the conditions we encountered sbound. We were still encountering occasional light chop/light turbulence in and out of the clouds and while in the clouds engine anti-ice was utilized with no visible ice accumulation, no buildups or areas of high moisture content were displayed on the radar and no deviations from course for WX were made. At approximately XA30Z we entered the tops of clouds and initiated engine anti-ice. We began to observe st elmo's fire and ice accumulating rapidly on both windshield wiper bolts and the first officer's window necessitating airfoil anti-ice as well. In the course of 3-5 mins, 1/2 - 1 inch of ice accumulated in these areas. Following the application of both engine anti-ice and airfoil anti-ice, we were notified by 2 of the flight attendants who were in the rear of the aircraft that they heard 2 pops or bangs, 1 from each side of the aircraft in the vicinity of the engines. They conveyed to us that the reason they heard the sounds was due to their position in the rear of the aircraft at the time and had they been further forward in the cabin they would not have heard the sounds. During the application of both engine anti-ice and, airfoil anti-ice, there were no abnormal engine indications nor were there any following the flight attendant's report. The first officer went to the rear of the aircraft and observed no abnormal engine sounds or vibrations. We exited the cloud approximately 7-8 mins after entering it and both engine anti-ice and airfoil anti-ice system were utilized until all visible ice had dissipated. An engine data monitoring form was filled out and the engines were monitored closely for the duration of the flight with no abnormal indications observed. Upon arrival sfo, the first officer and I communicated with the 2 company maintenance personnel who met the aircraft and informed them of our encounter. It was observed that a fan tip blade was bent on the left engine. It was ensured that the mechanics would inspect the right engine as well. In light of the bent fan tip blade, we communicated with the mechanics the necessity for an aircraft maintenance discrepancy write-up. The mechanics assured us that they would write-up the discrepancy following a more thorough inspection of both engines. They in fact did so refering our report to them and the flight attendant's report to us. Upon notification by our chief pilot the following morning, I was informed that there was damage to both engines to the extent unknown as of the writing of this report.

Related reports:

Google
 

Original NASA ASRS Text

Title: POSSIBLE ICING FOREIGN OBJECT DAMAGE STRUCK ENG FAN BLADES AND BENT THEM.

Narrative: DUE TO THE TURBULENT FLT CONDITIONS AT THE HIGHER ALTS, IT WAS DISCUSSED AND PLANNED THAT WE SHOULD CONSIDER FL280 FOR OUR RETURN LEG TO SFO AND THEREFORE PLAN ON FUEL FOR THE LOWER ALT AND POSSIBLE ENG ANTI-ICE. MINIMUM DISPATCH FUEL DEPARTING GDL WAS 29.2K LBS AND WE DEPARTED WITH 31.2K LBS. FIELD CONDITIONS DEPARTING GDL WERE CLR, WIND CALM, TEMP 20 DEGS C, RWY 28 AND NIGHT CONDITIONS. DURING CLB OUT OF GDL AND INITIAL CRUISE FLT CONDITIONS WERE CLR WITH THE SAME OCCASIONAL LIGHT CHOP/LIGHT TURB AFTER LEVELOFF AT FL280. AGAIN THE RPTS AT THE HIGHER ALTS WERE CONTINUOUS LIGHT TO MODERATE TURB AS RPTED BY OTHER ACFT AND CENTRAL MAZATLAN (CTR), THEREFORE, WE ELECTED TO REMAIN AT FL280. AFTER PASSING MZT, FLT CONDITIONS BECAME SIMILAR AS THOSE WE ENCOUNTERED SBOUND, WITH US IN THE TOPS OF THIN CLOUDS AND THEN IN THE CLR WITH THE PERIODS IN THE CLOUDS OF SHORTER DURATION AND THE PERIODS IN THE CLR OF LONGER DURATION THAN THE CONDITIONS WE ENCOUNTERED SBOUND. WE WERE STILL ENCOUNTERING OCCASIONAL LIGHT CHOP/LIGHT TURB IN AND OUT OF THE CLOUDS AND WHILE IN THE CLOUDS ENG ANTI-ICE WAS UTILIZED WITH NO VISIBLE ICE ACCUMULATION, NO BUILDUPS OR AREAS OF HIGH MOISTURE CONTENT WERE DISPLAYED ON THE RADAR AND NO DEVS FROM COURSE FOR WX WERE MADE. AT APPROX XA30Z WE ENTERED THE TOPS OF CLOUDS AND INITIATED ENG ANTI-ICE. WE BEGAN TO OBSERVE ST ELMO'S FIRE AND ICE ACCUMULATING RAPIDLY ON BOTH WINDSHIELD WIPER BOLTS AND THE FO'S WINDOW NECESSITATING AIRFOIL ANTI-ICE AS WELL. IN THE COURSE OF 3-5 MINS, 1/2 - 1 INCH OF ICE ACCUMULATED IN THESE AREAS. FOLLOWING THE APPLICATION OF BOTH ENG ANTI-ICE AND AIRFOIL ANTI-ICE, WE WERE NOTIFIED BY 2 OF THE FLT ATTENDANTS WHO WERE IN THE REAR OF THE ACFT THAT THEY HEARD 2 POPS OR BANGS, 1 FROM EACH SIDE OF THE ACFT IN THE VICINITY OF THE ENGS. THEY CONVEYED TO US THAT THE REASON THEY HEARD THE SOUNDS WAS DUE TO THEIR POS IN THE REAR OF THE ACFT AT THE TIME AND HAD THEY BEEN FURTHER FORWARD IN THE CABIN THEY WOULD NOT HAVE HEARD THE SOUNDS. DURING THE APPLICATION OF BOTH ENG ANTI-ICE AND, AIRFOIL ANTI-ICE, THERE WERE NO ABNORMAL ENG INDICATIONS NOR WERE THERE ANY FOLLOWING THE FLT ATTENDANT'S RPT. THE FO WENT TO THE REAR OF THE ACFT AND OBSERVED NO ABNORMAL ENG SOUNDS OR VIBRATIONS. WE EXITED THE CLOUD APPROX 7-8 MINS AFTER ENTERING IT AND BOTH ENG ANTI-ICE AND AIRFOIL ANTI-ICE SYS WERE UTILIZED UNTIL ALL VISIBLE ICE HAD DISSIPATED. AN ENG DATA MONITORING FORM WAS FILLED OUT AND THE ENGS WERE MONITORED CLOSELY FOR THE DURATION OF THE FLT WITH NO ABNORMAL INDICATIONS OBSERVED. UPON ARR SFO, THE FO AND I COMMUNICATED WITH THE 2 COMPANY MAINT PERSONNEL WHO MET THE ACFT AND INFORMED THEM OF OUR ENCOUNTER. IT WAS OBSERVED THAT A FAN TIP BLADE WAS BENT ON THE L ENG. IT WAS ENSURED THAT THE MECHS WOULD INSPECT THE R ENG AS WELL. IN LIGHT OF THE BENT FAN TIP BLADE, WE COMMUNICATED WITH THE MECHS THE NECESSITY FOR AN ACFT MAINT DISCREPANCY WRITE-UP. THE MECHS ASSURED US THAT THEY WOULD WRITE-UP THE DISCREPANCY FOLLOWING A MORE THOROUGH INSPECTION OF BOTH ENGS. THEY IN FACT DID SO REFERING OUR RPT TO THEM AND THE FLT ATTENDANT'S RPT TO US. UPON NOTIFICATION BY OUR CHIEF PLT THE FOLLOWING MORNING, I WAS INFORMED THAT THERE WAS DAMAGE TO BOTH ENGS TO THE EXTENT UNKNOWN AS OF THE WRITING OF THIS RPT.

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.