B757 captain reports disengaging autothrottles during descent and forgetting to reengage them as the...

Narrative:

I was monitoring the descent and had postponed some pilot not flying duties as the ride was quite rough and the need to coordinate with ATC. Clearance [was] given to cross arrival fix at 13;000 and 250 KTS. Reaching 13;000 the air smoothed out and I began setting up the approach and other duties that were delayed by the previous conditions and work load. I was unaware that the pilot flying had turned the autothrottle arm switch off for the descent with the autopilot still engaged. The aircraft continued slowing beyond 250 KTS and slowed to 10 KTS below clean bug speed. At this point both the captain and I noticed the low speed and acted accordingly to return to 250 KTS. I believe fatigue could have played a role in this event as we were delayed over 4 hours from original departure and I had been awake for over 14 hours when the event occurred.

Original NASA ASRS Text

Title: B757 Captain reports disengaging autothrottles during descent and forgetting to reengage them as the aircraft levels off on autopilot. Aircraft slows below clean maneuver airspeed before being noticed and power added. Fatigue was cited as a factor.

Narrative: I was monitoring the descent and had postponed some pilot not flying duties as the ride was quite rough and the need to coordinate with ATC. Clearance [was] given to cross arrival fix at 13;000 and 250 KTS. Reaching 13;000 the air smoothed out and I began setting up the approach and other duties that were delayed by the previous conditions and work load. I was unaware that the pilot flying had turned the autothrottle arm switch off for the descent with the autopilot still engaged. The aircraft continued slowing beyond 250 KTS and slowed to 10 KTS below clean bug speed. At this point both the Captain and I noticed the low speed and acted accordingly to return to 250 KTS. I believe fatigue could have played a role in this event as we were delayed over 4 hours from original departure and I had been awake for over 14 hours when the event occurred.

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.

Attributes
ACN	954361
Time
Date	201106
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.TRACON
State Reference	US
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Flight Phase	Descent
Flight Plan	IFR
Person 1
Function	Pilot Not Flying First Officer
Person 2
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Deviation - Procedural Published Material / Policy Deviation - Speed All Types

B757 captain reports disengaging autothrottles during descent and forgetting to reengage them as the aircraft levels off on autopilot. Aircraft slows below clean maneuver airspeed before being noticed and power added. Fatigue was cited as a factor.