Dhc-8-400 crew failed to level at FL240 following a 1;000 ft descent because the altitude sel mode c...

Attributes
ACN	1054094
Time
Date	201212
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Dash 8-400
Operating Under FAR Part	Part 121
Flight Phase	Descent
Flight Plan	IFR
Component
Aircraft Component	Altitude Alert
Person 1
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Commercial
Person 2
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Deviation - Altitude Overshoot Deviation - Procedural Published Material / Policy Deviation - Procedural Clearance

Narrative:

During descent; we were cleared to descend from FL250 to FL240 and to contact the next controller on a new frequency. The captain entered 24;000 ft into the autopilot; pushed the altitude sel button and initiated the descent. Upon initial check in with the new controller; I realized that altitude sel had somehow been deactivated and we were descending through FL233. I immediately notified the captain and he began to correct the deviation; I then advised ATC of our current altitude and we were then cleared to descend and maintain FL230. No further action was taken. Exercise additional vigilance while initiating 1;000 ft altitude changes; verify altitude sel activation more often during a 1;000 ft altitude change.

Original NASA ASRS Text

Title: DHC-8-400 crew failed to level at FL240 following a 1;000 FT descent because the ALT SEL mode control button was either not selected or was disengaged.

Narrative: During descent; we were cleared to descend from FL250 to FL240 and to contact the next Controller on a new frequency. The Captain entered 24;000 FT into the autopilot; pushed the ALT SEL button and initiated the descent. Upon initial check in with the new Controller; I realized that ALT SEL had somehow been deactivated and we were descending through FL233. I immediately notified the Captain and he began to correct the deviation; I then advised ATC of our current altitude and we were then cleared to descend and maintain FL230. No further action was taken. Exercise additional vigilance while initiating 1;000 FT altitude changes; verify ALT SEL activation more often during a 1;000 FT altitude change.

Data retrieved from NASA's ASRS site as of July 2013 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.

Dhc-8-400 crew failed to level at FL240 following a 1;000 ft descent because the altitude sel mode control button was either not selected or was disengaged.