<< >> NASA ASRS Report 1275303, June 2015

Enroute to diversion airport (for weather) crew of B-737 exceeded limit speed after the autothrottle disengaged and created an overspeed situation.

Attributes
ACN	1275303
Time
Date	201506
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	Throttle/Power Lever
Person 1
Function	Captain
Experience	Flight Crew Last 90 Days 239 Flight Crew Type 239
Events
Anomaly	Deviation - Speed All Types

Narrative:

In a newer model aircraft; the autothrottle disconnected and would not reengage. During cruise at FL380 in turbulence; the speed increased rather suddenly to mach .83 and the airspeed warning clacker sounded. The thrust was reduced and aircraft speed was brought back within limits. It was a busy phase of flight as we were in the process of having to divert. After landing; dispatch and maintenance were notified and a logbook entry was made.this might have been avoided altogether by selecting a slightly lower cruise mach speed; or a lower altitude; but more vigilance by both pilots would have been the only way to prevent this overspeed.

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Original NASA ASRS Text

Title: Enroute to diversion airport (for weather) crew of B-737 exceeded limit speed after the autothrottle disengaged and created an overspeed situation.

Narrative: In a newer model aircraft; the autothrottle disconnected and would not reengage. During cruise at FL380 in turbulence; the speed increased rather suddenly to Mach .83 and the Airspeed Warning Clacker sounded. The thrust was reduced and aircraft speed was brought back within limits. It was a busy phase of flight as we were in the process of having to divert. After landing; Dispatch and Maintenance were notified and a logbook entry was made.This might have been avoided altogether by selecting a slightly lower cruise Mach speed; or a lower altitude; but more vigilance by both pilots would have been the only way to prevent this overspeed.

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.