B737-800
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Distraction; Troubleshooting
Aircraft Equipment Problem Critical
Flight Crew Returned To Gate; General Flight Cancelled / Delayed
Aircraft
While starting #2 engine during push back; the flight deck crew heard an unusual; but unidentified; noise. At approximately 23% N2; the First Officer observed N2 RPM stopped increasing and began to decrease. At about the same time; the tug driver reported sparks and smoke coming from the #2 engine. The stop attempt was terminated (fuel had not been introduced) and the aircraft was returned to the gate and subsequently taken out of service.
B737-800 Captain reported an unknown noise and lack of power while starting the number two engine.