Air carrier medium large transport altitude deviation overshot during descent.

Attributes
ACN	122959
Time
Date	198909
Day	Thu
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : lga
State Reference	NY
Altitude	msl bound lower : 8000 msl bound upper : 9000
Environment
Flight Conditions	Mixed
Light	Night
Aircraft 1
Controlling Facilities	tracon : n90
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : cfi pilot : atp
Experience	flight time last 90 days : 200 flight time total : 7000 flight time type : 3000
ASRS Report	122959
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	other flight crewa
Resolutory Action	controller : issued new clearance
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Descending into lga clearance was given to 9000'. Both myself and captain remember verifying altitude selector set with 9000' in window. Circuit breaker's ahead with tops about 12000' with no clear way around them. I called, 'I'm off the radios,' to tell the F/a's in back to be seated for possible rough air. When I finished the aircraft was just leveling, but when I looked at the altimeter it read 8000' instead of 9000'. My eyes went right to the altitude window and 8000' was in the window. I asked the captain if we were cleared to 8000', thinking clearance was given while I was off the air. He responded he thought the clearance was to 9000', so I called the controller and requested assigned altitude for our aircraft. He came back with 'maintain 8000'.' I have read a bulletin that says that the medium large transport's altitude selector has been known to move maybe when just in the click between altitudes. As aircraft become more automated human x-chking naturally declines and will cause many problems.

Original NASA ASRS Text

Title: ACR MLG ALT DEVIATION OVERSHOT DURING DESCENT.

Narrative: DSNDING INTO LGA CLRNC WAS GIVEN TO 9000'. BOTH MYSELF AND CAPT REMEMBER VERIFYING ALT SELECTOR SET WITH 9000' IN WINDOW. CB'S AHEAD WITH TOPS ABOUT 12000' WITH NO CLR WAY AROUND THEM. I CALLED, 'I'M OFF THE RADIOS,' TO TELL THE F/A'S IN BACK TO BE SEATED FOR POSSIBLE ROUGH AIR. WHEN I FINISHED THE ACFT WAS JUST LEVELING, BUT WHEN I LOOKED AT THE ALTIMETER IT READ 8000' INSTEAD OF 9000'. MY EYES WENT RIGHT TO THE ALT WINDOW AND 8000' WAS IN THE WINDOW. I ASKED THE CAPT IF WE WERE CLRED TO 8000', THINKING CLRNC WAS GIVEN WHILE I WAS OFF THE AIR. HE RESPONDED HE THOUGHT THE CLRNC WAS TO 9000', SO I CALLED THE CTLR AND REQUESTED ASSIGNED ALT FOR OUR ACFT. HE CAME BACK WITH 'MAINTAIN 8000'.' I HAVE READ A BULLETIN THAT SAYS THAT THE MLG'S ALT SELECTOR HAS BEEN KNOWN TO MOVE MAYBE WHEN JUST IN THE CLICK BTWN ALTS. AS ACFT BECOME MORE AUTOMATED HUMAN X-CHKING NATURALLY DECLINES AND WILL CAUSE MANY PROBS.

Data retrieved from NASA's ASRS site as of August 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.