B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 215
Aircraft Equipment Problem Less Severe
Aircraft Equipment Problem Dissipated; Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport; General Maintenance Action
Aircraft
Our flight departed and was climbing through 11;000 feet when the Number1 engine began to surge. N1 was fluctuating between 100-70 percent. As you would expect; this caused substantial aircraft yaw. The F/O (Pilot Flying) immediately recognized the condition and executed the QRH memory items for engine surge by disconnecting the autothrottles and pulling back the thrust levers to about mid range. Simultaneously the Number 2 engine began to fluctuate but to a lesser degree of approximately 95-80 percent. After about 15-30 seconds with the thrust levers in the reduced position; both engines stabilized at approximately 70% N1. Our flight was approximately 20 miles northeast of the departure airport when this event started and the weather was clear with unlimited visibility. We quickly determined that returning would be our safest course of action. ATC gave us vectors back to the field and we landed without further incident. On landing roll; both Number 1 and Number 2 ENG CONTROL lights illuminated. Upon arrival at the gate; Maintenance was notified and the aircraft was subsequently taken out of service.
During climbout passing through approximately 11;000 feet; the Number 1 engine started to fluctuate in N1. The fluctuation was severe enough to cause significant yaw. I disconnected the autothrottles and reduced thrust to maintain engine limits. Shortly after that the Number 2 engine started fluctuating also. Further thrust reduction on both engines to about 70% seemed to stop the variations. We accomplished the Engine Limit/Surge/Stall Checklist. We then requested a return. Once we turned south and descended; we were handed off to Approach and cleared for the visual approach. During the descent and approach phase of flight; the engines seemed to operate normally. Normal landing and taxi back to the gate were uneventful.
B737-700 flight crew experiences fluctuating N1 on the left engine climbing through 11;000 feet. Auto thrust is turned off with no change then the thrust is reduced until stability returns at about 70 percent N1. The right engine also experienced brief N1 fluctuations and the crew returns uneventfully to the departure airport.