Air carrier medium large transport altitude deviation excursion from clearance altitude.

Attributes
ACN	132725
Time
Date	198912
Day	Thu
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : pvd
State Reference	RI
Altitude	msl bound lower : 26400 msl bound upper : 27000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zbw
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise other descent other
Route In Use	enroute airway : zbw
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 75 flight time total : 7000 flight time type : 2000
ASRS Report	132725
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : flight engineer
Experience	flight time total : 10800
ASRS Report	132059
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

About 125 mi out of pvd I was picking up the ATIS. We were in cruise at 27,000'. I noticed the captain check his approach plate and then set 24,000 in the altitude window. Shortly after that he pressed 'execute' on the pms and the aircraft started a descent. I assumed ATC had given us 24,000' while I was getting the ATIS and I was just about to ask the captain when ATC asked what our altitude was. I looked at the captain and asked if he gave us 24,000. He didn't answer. I didn't answer ATC because I did not know what was going on. ATC informed us that our altitude showed 600' low, at which point I understood that we should still be at 27,000'. I tried to convey to the captain that we should still be at 27,000 but it took him a few seconds to get the point. He began to correct his mistake when ATC told us to descend to 24,000. After the incident, the captain swears that I asked for a lower altitude and that I set 24,000 in the altitude window. I told him that I did not. He was certain that I asked for and set 24,000 in the altitude window. I told him that I did not. I monitored the captain very carefully after that. I should have questioned the captain immediately when he set 24,000 in the altitude window but it seemed like he knew what he was doing and I assumed I missed the call while getting the ATIS. The whole thing was very strange!

Original NASA ASRS Text

Title: ACR MLG ALT DEVIATION EXCURSION FROM CLRNC ALT.

Narrative: ABOUT 125 MI OUT OF PVD I WAS PICKING UP THE ATIS. WE WERE IN CRUISE AT 27,000'. I NOTICED THE CAPT CHECK HIS APCH PLATE AND THEN SET 24,000 IN THE ALT WINDOW. SHORTLY AFTER THAT HE PRESSED 'EXECUTE' ON THE PMS AND THE ACFT STARTED A DSCNT. I ASSUMED ATC HAD GIVEN US 24,000' WHILE I WAS GETTING THE ATIS AND I WAS JUST ABOUT TO ASK THE CAPT WHEN ATC ASKED WHAT OUR ALT WAS. I LOOKED AT THE CAPT AND ASKED IF HE GAVE US 24,000. HE DIDN'T ANSWER. I DIDN'T ANSWER ATC BECAUSE I DID NOT KNOW WHAT WAS GOING ON. ATC INFORMED US THAT OUR ALT SHOWED 600' LOW, AT WHICH POINT I UNDERSTOOD THAT WE SHOULD STILL BE AT 27,000'. I TRIED TO CONVEY TO THE CAPT THAT WE SHOULD STILL BE AT 27,000 BUT IT TOOK HIM A FEW SECONDS TO GET THE POINT. HE BEGAN TO CORRECT HIS MISTAKE WHEN ATC TOLD US TO DSND TO 24,000. AFTER THE INCIDENT, THE CAPT SWEARS THAT I ASKED FOR A LOWER ALT AND THAT I SET 24,000 IN THE ALT WINDOW. I TOLD HIM THAT I DID NOT. HE WAS CERTAIN THAT I ASKED FOR AND SET 24,000 IN THE ALT WINDOW. I TOLD HIM THAT I DID NOT. I MONITORED THE CAPT VERY CAREFULLY AFTER THAT. I SHOULD HAVE QUESTIONED THE CAPT IMMEDIATELY WHEN HE SET 24,000 IN THE ALT WINDOW BUT IT SEEMED LIKE HE KNEW WHAT HE WAS DOING AND I ASSUMED I MISSED THE CALL WHILE GETTING THE ATIS. THE WHOLE THING WAS VERY STRANGE!

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.