Altitude deviation.

Attributes
ACN	295961
Time
Date	199502
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : orw
State Reference	CT
Altitude	msl bound lower : 9700 msl bound upper : 10000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other descent : approach descent other
Route In Use	enroute airway : pvd
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial pilot : cfi pilot : atp
Experience	flight time last 90 days : 164 flight time total : 4500 flight time type : 2200
ASRS Report	295961
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : became reoriented flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I was hand flying the airplane due to inoperative autoplt because of failure of captain's pitot source which drives/provides information to the air data computer which provides signals to the autoplt. During this time vmo horn sounded due to malfunction of captain's airspeed indicator, true airspeed and static air temperature data dropped off our EFIS screens and we were trying to trouble-shoot the various malfunctions. Approach then cleared us from 11000 ft MSL to 10000 ft MSL. While hand flying the airplane and being distracted by the aforementioned problems, I descended to 9700 ft MSL and was apprised of this by our altitude alerter which sounds off at 300 ft low and by captain who noticed my altitude simultaneously. I immediately climbed back up to 10000 ft MSL. We said nothing to the controller. The controller called us out as traffic to another airplane as 'level at 10000 ft' (I believe he was being charitable) and apparently there was no conflict with any other aircraft.why did this happen? 1) PF distracted by overspd horn. True airspeed and static air temperature data loss, and helping PNF trouble-shoot. How could this have been prevented? 1) PF flies airplane, lets PNF trouble-shoot. 2) use of standard altitude callouts (1000 ft and 500 ft above, leveling).

Original NASA ASRS Text

Title: ALTDEV.

Narrative: I WAS HAND FLYING THE AIRPLANE DUE TO INOP AUTOPLT BECAUSE OF FAILURE OF CAPT'S PITOT SOURCE WHICH DRIVES/PROVIDES INFO TO THE AIR DATA COMPUTER WHICH PROVIDES SIGNALS TO THE AUTOPLT. DURING THIS TIME VMO HORN SOUNDED DUE TO MALFUNCTION OF CAPT'S AIRSPD INDICATOR, TRUE AIRSPD AND STATIC AIR TEMP DATA DROPPED OFF OUR EFIS SCREENS AND WE WERE TRYING TO TROUBLE-SHOOT THE VARIOUS MALFUNCTIONS. APCH THEN CLRED US FROM 11000 FT MSL TO 10000 FT MSL. WHILE HAND FLYING THE AIRPLANE AND BEING DISTRACTED BY THE AFOREMENTIONED PROBS, I DSNDED TO 9700 FT MSL AND WAS APPRISED OF THIS BY OUR ALT ALERTER WHICH SOUNDS OFF AT 300 FT LOW AND BY CAPT WHO NOTICED MY ALT SIMULTANEOUSLY. I IMMEDIATELY CLBED BACK UP TO 10000 FT MSL. WE SAID NOTHING TO THE CTLR. THE CTLR CALLED US OUT AS TFC TO ANOTHER AIRPLANE AS 'LEVEL AT 10000 FT' (I BELIEVE HE WAS BEING CHARITABLE) AND APPARENTLY THERE WAS NO CONFLICT WITH ANY OTHER ACFT.WHY DID THIS HAPPEN? 1) PF DISTRACTED BY OVERSPD HORN. TRUE AIRSPD AND STATIC AIR TEMP DATA LOSS, AND HELPING PNF TROUBLE-SHOOT. HOW COULD THIS HAVE BEEN PREVENTED? 1) PF FLIES AIRPLANE, LETS PNF TROUBLE-SHOOT. 2) USE OF STANDARD ALT CALLOUTS (1000 FT AND 500 FT ABOVE, LEVELING).

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.