Large transport air carrier aircraft had decreasing B system hydraulic fluid and pump light. Flight crew turned off the pump as aircraft, on autoplt, pitched up and climbed 400 ft before reporter could react and return to assigned altitude. Emergency declared and landed at destination airport.

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Attributes
ACN	383206
Time
Date	199709
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : zme
State Reference	TN
Altitude	msl bound lower : 28000 msl bound upper : 28400
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zme tower : phx
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 20 flight time total : 10000 flight time type : 4500
ASRS Report	383206
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : declared emergency flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

In cruise flight on autoplt at FL280, B system hydraulic light (pump) came on. Noticed fluid decreasing. Turned off B electric pumps. Just after attention was drawn to hydraulic panel, the nose pitched up and the aircraft began to climb despite the fact the autoplt was on altitude hold and in the a channel. I disconnected the autoplt and the trim was very nose high. I retrimmed while stiff arming the control column to stop the nose from pitching up further. We gained approximately 400 ft before we started back down to FL280. We declared an emergency going into denver airport and executed an uneventful partial flap landing. It was not clear what the connection was between the B system hydraulic and the a channel autoplt, but after the hydraulic system was repaired, the autoplt worked normally. (A channel autoplt uses a system hydraulic.) the distraction of the hydraulic failure with attendant procedures contributed to the altitude deviation.

Original NASA ASRS Text

Title: LGT ACR ACFT HAD DECREASING B SYS HYD FLUID AND PUMP LIGHT. FLC TURNED OFF THE PUMP AS ACFT, ON AUTOPLT, PITCHED UP AND CLBED 400 FT BEFORE RPTR COULD REACT AND RETURN TO ASSIGNED ALT. EMER DECLARED AND LANDED AT DEST ARPT.

Narrative: IN CRUISE FLT ON AUTOPLT AT FL280, B SYS HYD LIGHT (PUMP) CAME ON. NOTICED FLUID DECREASING. TURNED OFF B ELECTRIC PUMPS. JUST AFTER ATTN WAS DRAWN TO HYD PANEL, THE NOSE PITCHED UP AND THE ACFT BEGAN TO CLB DESPITE THE FACT THE AUTOPLT WAS ON ALT HOLD AND IN THE A CHANNEL. I DISCONNECTED THE AUTOPLT AND THE TRIM WAS VERY NOSE HIGH. I RETRIMMED WHILE STIFF ARMING THE CTL COLUMN TO STOP THE NOSE FROM PITCHING UP FURTHER. WE GAINED APPROX 400 FT BEFORE WE STARTED BACK DOWN TO FL280. WE DECLARED AN EMER GOING INTO DENVER ARPT AND EXECUTED AN UNEVENTFUL PARTIAL FLAP LNDG. IT WAS NOT CLR WHAT THE CONNECTION WAS BTWN THE B SYS HYD AND THE A CHANNEL AUTOPLT, BUT AFTER THE HYD SYS WAS REPAIRED, THE AUTOPLT WORKED NORMALLY. (A CHANNEL AUTOPLT USES A SYS HYD.) THE DISTR OF THE HYD FAILURE WITH ATTENDANT PROCS CONTRIBUTED TO THE ALTDEV.

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.