Flight crew of a DC10-30 cargo flight, hauling horses, descended below assigned altitude due to distraction of ATC instructions and no warning from the altitude alerter.

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Attributes
ACN	383630
Time
Date	199710
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : trm
State Reference	CA
Altitude	msl bound lower : 30600 msl bound upper : 31000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zla
Operator	common carrier : air carrier
Make Model Name	DC-10 30F
Navigation In Use	Other
Flight Phase	descent other
Route In Use	arrival other arrival star : star enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 2500 flight time type : 200
ASRS Report	383630
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 14500 flight time type : 2600
ASRS Report	383510
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

ATC gave us a vector, an altitude change (from FL350 to FL310), and an airspeed reduction. As we approached FL310, we shallowed the descent due to our sensitive cargo (horses) and the '1000 ft above' call was made. However, the altitude alert horn did not sound and there may have been some task saturation with ATC's instructions. We descended about 400 ft below FL310, recognized our mistake, and immediately corrected it. No conflict occurred. Supplemental information from acn 383510: last 1000 ft, used manual control of vertical speed due to horses on board. Must have inadvertently disconnected automatic capture/altitude hold. Nothing said by ZLA.

Original NASA ASRS Text

Title: FLC OF A DC10-30 CARGO FLT, HAULING HORSES, DSNDED BELOW ASSIGNED ALT DUE TO DISTR OF ATC INSTRUCTIONS AND NO WARNING FROM THE ALT ALERTER.

Narrative: ATC GAVE US A VECTOR, AN ALT CHANGE (FROM FL350 TO FL310), AND AN AIRSPD REDUCTION. AS WE APCHED FL310, WE SHALLOWED THE DSCNT DUE TO OUR SENSITIVE CARGO (HORSES) AND THE '1000 FT ABOVE' CALL WAS MADE. HOWEVER, THE ALT ALERT HORN DID NOT SOUND AND THERE MAY HAVE BEEN SOME TASK SATURATION WITH ATC'S INSTRUCTIONS. WE DSNDED ABOUT 400 FT BELOW FL310, RECOGNIZED OUR MISTAKE, AND IMMEDIATELY CORRECTED IT. NO CONFLICT OCCURRED. SUPPLEMENTAL INFO FROM ACN 383510: LAST 1000 FT, USED MANUAL CTL OF VERT SPD DUE TO HORSES ON BOARD. MUST HAVE INADVERTENTLY DISCONNECTED AUTO CAPTURE/ALT HOLD. NOTHING SAID BY ZLA.

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.