An air carrier flight crew flying an EMB120 near iah fails to level at altitude as assigned by ATC.

Attributes
ACN	483590
Time
Date	200008
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : iah.bcstn
State Reference	TX
Altitude	msl single value : 18000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zhu.artcc
Operator	common carrier : air carrier
Make Model Name	Brasilia EMB-120 All Series
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	climbout : intermediate altitude
Route In Use	departure : other published ifr departure
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : instrument pilot : multi engine
Experience	flight time last 90 days : 265 flight time total : 7235 flight time type : 1265
ASRS Report	483594
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial pilot : multi engine
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance
Independent Detector	aircraft equipment : altitude alert other flight crewa other flight crewb
Resolutory Action	flight crew : overcame equipment problem flight crew : returned to assigned altitude
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were cleared to climb and maintain FL180. Autoplt was on. When the altitude alerter was set to FL180, altitude capture on the flight director went off. This happens on occasion and neither of us noticed it. At FL183, the altitude alerter chimed. The first officer immediately disengaged the autoplt and descended to FL180. Paying closer attention to the flight director control panel when changing the altitude alerter would have prevented this.

Original NASA ASRS Text

Title: AN ACR FLC FLYING AN EMB120 NEAR IAH FAILS TO LEVEL AT ALT AS ASSIGNED BY ATC.

Narrative: WE WERE CLRED TO CLB AND MAINTAIN FL180. AUTOPLT WAS ON. WHEN THE ALT ALERTER WAS SET TO FL180, ALT CAPTURE ON THE FLT DIRECTOR WENT OFF. THIS HAPPENS ON OCCASION AND NEITHER OF US NOTICED IT. AT FL183, THE ALT ALERTER CHIMED. THE FO IMMEDIATELY DISENGAGED THE AUTOPLT AND DSNDED TO FL180. PAYING CLOSER ATTN TO THE FLT DIRECTOR CTL PANEL WHEN CHANGING THE ALT ALERTER WOULD HAVE PREVENTED THIS.

Data retrieved from NASA's ASRS site as of July 2007 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.