First officer of a B737-400 allowed the aircraft to ascend above assigned altitude when slowing the aircraft for descent due misprogramming the FMC automatic hold before it was time for their descent.

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Attributes
ACN	401193
Time
Date	199805
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : btg airport : sea
State Reference	WA
Altitude	msl bound lower : 31000 msl bound upper : 31800
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zse
Operator	common carrier : air carrier
Make Model Name	B737-400
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	arrival other arrival star : star
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : atp pilot : commercial
Experience	flight time last 90 days : 140 flight time total : 15000 flight time type : 140
ASRS Report	401193
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : commercial pilot : cfi pilot : atp
Experience	flight time last 90 days : 160 flight time total : 11000 flight time type : 4800
ASRS Report	401090
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

ZSE was slowing us down and giving us vectors for spacing into seattle. Approximately 40 mi from top of descent, we were cleared, pilot's discretion, to FL240, which we set in the altitude alerter. The first officer was PF and responded to ATC as I was off frequency to get ATIS. A flight attendant came up at that time to take away our meal trays and remind us that a medical oxygen bottle was needed in seattle on landing. When I turned forward, I noticed that we were turning back to btg per ATC instructions, but the autoplt was in control wheel steering pitch mode. A quick glance at the altitude showed that we were climbing and passing FL316. (Assigned altitude was FL310.) I grabbed the controls and gently pushed the elevator over to get us back to FL310. Our altimeter showed we got to FL318 before we started back down. No altitude alerter went off because we had FL240 in the MCP. I am not sure how the aircraft got into control wheel steering pitch mode, but the lack of any bells, my attention diverted to the flight attendant, busy ATC instructions, and the first officer not noticing what mode the airplane had downgraded to, caused us to bust our altitude.

Original NASA ASRS Text

Title: FO OF A B737-400 ALLOWED THE ACFT TO ASCEND ABOVE ASSIGNED ALT WHEN SLOWING THE ACFT FOR DSCNT DUE MISPROGRAMMING THE FMC AUTO HOLD BEFORE IT WAS TIME FOR THEIR DSCNT.

Narrative: ZSE WAS SLOWING US DOWN AND GIVING US VECTORS FOR SPACING INTO SEATTLE. APPROX 40 MI FROM TOP OF DSCNT, WE WERE CLRED, PLT'S DISCRETION, TO FL240, WHICH WE SET IN THE ALT ALERTER. THE FO WAS PF AND RESPONDED TO ATC AS I WAS OFF FREQ TO GET ATIS. A FLT ATTENDANT CAME UP AT THAT TIME TO TAKE AWAY OUR MEAL TRAYS AND REMIND US THAT A MEDICAL OXYGEN BOTTLE WAS NEEDED IN SEATTLE ON LNDG. WHEN I TURNED FORWARD, I NOTICED THAT WE WERE TURNING BACK TO BTG PER ATC INSTRUCTIONS, BUT THE AUTOPLT WAS IN CTL WHEEL STEERING PITCH MODE. A QUICK GLANCE AT THE ALT SHOWED THAT WE WERE CLBING AND PASSING FL316. (ASSIGNED ALT WAS FL310.) I GRABBED THE CTLS AND GENTLY PUSHED THE ELEVATOR OVER TO GET US BACK TO FL310. OUR ALTIMETER SHOWED WE GOT TO FL318 BEFORE WE STARTED BACK DOWN. NO ALT ALERTER WENT OFF BECAUSE WE HAD FL240 IN THE MCP. I AM NOT SURE HOW THE ACFT GOT INTO CTL WHEEL STEERING PITCH MODE, BUT THE LACK OF ANY BELLS, MY ATTN DIVERTED TO THE FLT ATTENDANT, BUSY ATC INSTRUCTIONS, AND THE FO NOT NOTICING WHAT MODE THE AIRPLANE HAD DOWNGRADED TO, CAUSED US TO BUST OUR ALT.

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.