B737NG flight crew reported they discharged a fire bottle into the engine when it did not shut down ...

Attributes
ACN	1412990
Time
Date	201612
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Taxi
Flight Plan	IFR
Component
Aircraft Component	Engine Starting System
Person 1
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 210 Flight Crew Type 974
Person 2
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy

Narrative:

[Event occurred during] pushback. After engine no 1 start we had an idg light on the left engine...we talked to maintenance and returned to gate. The left engine did not shut down with start lever. We pulled the fire handle and the engine still did not shut down. The engine kept running and was making loud noises and an unusual vibration. I had the flight attendants deplane the aircraft. I was worried that the engine might catch fire so I decided to fire one of the fire bottles; hoping that would shut down the engine. I decided to save the other fire bottle. We were very confused by the engine indications and the fact that the fire handle did not work.it turned out that the engine had shut down but the air valve to the starter stayed open. That was causing the loud noise and vibration. The air valve did not close with the fire handle being pulled. After about 10 minutes maintenance decided to close the APU valve and the engine finally spooled down. I am writing this [report] because I fired the fire bottle without a fire. I was worried about the vibration and confusing engine indications.

Original NASA ASRS Text

Title: B737NG flight crew reported they discharged a fire bottle into the engine when it did not shut down with the fuel handle or the fire handle. Apparently the starter valve remained open even after the attempted shut down.

Narrative: [Event occurred during] pushback. After engine no 1 start we had an IDG light on the left engine...we talked to maintenance and returned to gate. The left engine did not shut down with start lever. We pulled the fire handle and the engine still did not shut down. The engine kept running and was making loud noises and an unusual vibration. I had the flight attendants deplane the aircraft. I was worried that the engine might catch fire so I decided to fire one of the fire bottles; hoping that would shut down the engine. I decided to save the other fire bottle. We were very confused by the engine indications and the fact that the fire handle did not work.It turned out that the engine had shut down but the air valve to the starter stayed open. That was causing the loud noise and vibration. The air valve did not close with the fire handle being pulled. After about 10 minutes maintenance decided to close the APU valve and the engine finally spooled down. I am writing this [report] because I fired the fire bottle without a fire. I was worried about the vibration and confusing engine indications.

Data retrieved from NASA's ASRS site 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.