Altitude deviation. Overshoot on descent.

Attributes
ACN	142505
Time
Date	199004
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : phl
State Reference	PA
Altitude	msl bound lower : 7600 msl bound upper : 8000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : phl
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 120 flight time total : 3500 flight time type : 300
ASRS Report	142505
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 non adherence : required legal separation
Independent Detector	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:

The flight originated in tampa, fl, to philadelphia, PA. The aircraft had a MEL deferred altitude alerter. The captain explained before takeoff that we needed to be extra cautious about all altitude changes. While arriving into the philadelphia terminal area, we were assigned an altitude of 8000' from 10000'. During the descent, the pressurization system failed to operate. The captain (the PNF) immediately applied all of his attention to fix the system, and did not provide the callout 'one to go' (1000' to go). I was suddenly distracted by ATC notice of traffic that was very close to our position. As a result of the distrs, I did not level off at 8000' but 7600'. I noticed the altitude deviation within seconds, and immediately returned to 8000' with no known incident. The altitude deviation was caused by two major distrs. Pressurization failure and the captain's full attention, and the ATC call of close traffic. Even with these distrs, an operable altitude alerter would have prevented this! To avoid this problem on aircraft having only a two man crew, altitude alerters should not be deferrable! The workload is high enough.

Original NASA ASRS Text

Title: ALT DEVIATION. OVERSHOOT ON DESCENT.

Narrative: THE FLT ORIGINATED IN TAMPA, FL, TO PHILADELPHIA, PA. THE ACFT HAD A MEL DEFERRED ALT ALERTER. THE CAPT EXPLAINED BEFORE TKOF THAT WE NEEDED TO BE EXTRA CAUTIOUS ABOUT ALL ALT CHANGES. WHILE ARRIVING INTO THE PHILADELPHIA TERMINAL AREA, WE WERE ASSIGNED AN ALT OF 8000' FROM 10000'. DURING THE DSNT, THE PRESSURIZATION SYS FAILED TO OPERATE. THE CAPT (THE PNF) IMMEDIATELY APPLIED ALL OF HIS ATTN TO FIX THE SYS, AND DID NOT PROVIDE THE CALLOUT 'ONE TO GO' (1000' TO GO). I WAS SUDDENLY DISTRACTED BY ATC NOTICE OF TFC THAT WAS VERY CLOSE TO OUR POS. AS A RESULT OF THE DISTRS, I DID NOT LEVEL OFF AT 8000' BUT 7600'. I NOTICED THE ALT DEVIATION WITHIN SECS, AND IMMEDIATELY RETURNED TO 8000' WITH NO KNOWN INCIDENT. THE ALT DEVIATION WAS CAUSED BY TWO MAJOR DISTRS. PRESSURIZATION FAILURE AND THE CAPT'S FULL ATTN, AND THE ATC CALL OF CLOSE TFC. EVEN WITH THESE DISTRS, AN OPERABLE ALT ALERTER WOULD HAVE PREVENTED THIS! TO AVOID THIS PROB ON ACFT HAVING ONLY A TWO MAN CREW, ALT ALERTERS SHOULD NOT BE DEFERRABLE! THE WORKLOAD IS HIGH ENOUGH.

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.