Narrative:

Approaching 800 ft MSL; sfo tower instructed us to contact departure control. While my eyes were in the cockpit; the first officer (pilot flying) said 'birds' and I quickly looked up to see a flash go by my left as a group of birds passed by in the illumination of the landing lights. The first officer stated later that he thought he saw 4 birds pass the left side and one on the right. I felt a thump and immediately; there was a change in sound coming from one of the engines. The engine did not surge or fluctuate. The sound was a constant frequency like someone turned on a very noisy ventilation fan. I also noticed a small vibration that was associated with the noise. I scanned the engine instruments and all parameters were stable in the normal range except for the left engine vibration. It showed an elevated reading for N1 with a value of 2.5. That's not alarmingly high; but it was elevated none the less. The right engine's N1 value was 0.3. When we reduced the thrust to climb thrust; I noticed a decrease in the frequency of the noise and a slight decrease in the vibration level. At this point; I was pretty sure the bird or birds impacted the left engine and caused fan blade damage. We leveled off at 5;000 ft MSL and with the power back; the vibration and noise reduced to almost undetectable levels. Because of this; I did not feel we had severe damage and I chose not to perform the engine fire/severe damage/separation checklist. I felt we could keep the engine running. However; I was concerned that we took enough damage to that engine that we needed to make a precautionary landing back at sfo. I talked to the passengers and told them what had apparently happened and then I talked to the chief purser and he asked me if I wanted him to do anything special; hinting at prep. I said no; a prep would not be necessary; it would be a normal landing and that he could do a cabin advisory. We informed ATC that we were going to return to sfo. I sent an ACARS to dispatch to call me. I then sent him an ACARS message that we had a bird strike and we were returning to sfo. Shortly thereafter; dispatch called me and we had a brief discussion informing him what we were doing. He asked if I wanted to talk to maintenance; however; at that point; we knew we would be returning to sfo; our best option. I did not see maintenance being of a lot of help to us at that moment. Maintenance could look at it on the ground. Around this time; ATC had us near the final approach about 12 to 15 miles from the field. Dispatch said he would work on notifying everyone and we ended our discussion. When I rejoined with the first officer; ATC asked if we were ready to turn toward the field. At that point I felt we were ready to make the approach and landing. We then did a quick brief for a visual approach and I ran all the appropriate checklists. The first officer flew the approach and landing. We were 3;000 pounds over maximum landing weight and the first officer made a nice soft landing on runway 28L. After exiting the runway; we shut down the left engine and taxied to the gate. After the parking checklist was complete; we made sure to logbook the overweight landing and the bird strike. We viewed the left engine inlet and noted 6 to 8 fan blades with significant damage due to the bird strike.

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Original NASA ASRS Text

Title: An Air Carrier aircraft departed SFO Runway 1R and struck a flock of birds at about 700 FT damaging the left engine. The crew returned to land and found 6-8 blades with significant damage.

Narrative: Approaching 800 FT MSL; SFO Tower instructed us to contact Departure Control. While my eyes were in the cockpit; the First Officer (pilot flying) said 'birds' and I quickly looked up to see a flash go by my left as a group of birds passed by in the illumination of the landing lights. The First Officer stated later that he thought he saw 4 birds pass the left side and one on the right. I felt a thump and immediately; there was a change in sound coming from one of the engines. The engine did not surge or fluctuate. The sound was a constant frequency like someone turned on a very noisy ventilation fan. I also noticed a small vibration that was associated with the noise. I scanned the engine instruments and all parameters were stable in the normal range except for the left engine vibration. It showed an elevated reading for N1 with a value of 2.5. That's not alarmingly high; but it was elevated none the less. The right engine's N1 value was 0.3. When we reduced the thrust to climb thrust; I noticed a decrease in the frequency of the noise and a slight decrease in the vibration level. At this point; I was pretty sure the bird or birds impacted the left engine and caused fan blade damage. We leveled off at 5;000 FT MSL and with the power back; the vibration and noise reduced to almost undetectable levels. Because of this; I did not feel we had severe damage and I chose not to perform the Engine Fire/Severe Damage/Separation checklist. I felt we could keep the engine running. However; I was concerned that we took enough damage to that engine that we needed to make a precautionary landing back at SFO. I talked to the passengers and told them what had apparently happened and then I talked to the Chief Purser and he asked me if I wanted him to do anything special; hinting at prep. I said no; a prep would not be necessary; it would be a normal landing and that he could do a cabin advisory. We informed ATC that we were going to return to SFO. I sent an ACARS to Dispatch to call me. I then sent him an ACARS message that we had a bird strike and we were returning to SFO. Shortly thereafter; Dispatch called me and we had a brief discussion informing him what we were doing. He asked if I wanted to talk to Maintenance; however; at that point; we knew we would be returning to SFO; our best option. I did not see Maintenance being of a lot of help to us at that moment. Maintenance could look at it on the ground. Around this time; ATC had us near the final approach about 12 to 15 miles from the field. Dispatch said he would work on notifying everyone and we ended our discussion. When I rejoined with the First Officer; ATC asked if we were ready to turn toward the field. At that point I felt we were ready to make the approach and landing. We then did a quick brief for a visual approach and I ran all the appropriate checklists. The First Officer flew the approach and landing. We were 3;000 LBS over maximum landing weight and the First Officer made a nice soft landing on Runway 28L. After exiting the runway; we shut down the left engine and taxied to the gate. After the parking checklist was complete; we made sure to logbook the overweight landing and the bird strike. We viewed the left engine inlet and noted 6 to 8 fan blades with significant damage due to the bird strike.

Data retrieved from NASA's ASRS site as of April 2012 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.