Altitude deviation. Excursion from assigned.

Attributes
ACN	139466
Time
Date	199003
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : alb
State Reference	NY
Altitude	msl bound lower : 37000 msl bound upper : 37700
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zbw
Operator	common carrier : air carrier
Make Model Name	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 : atp pilot : flight engineer
Experience	flight time last 90 days : 150 flight time total : 12300 flight time type : 350
ASRS Report	139466
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 : 15000 flight time type : 400
ASRS Report	139485
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude other anomaly other
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:

Requested initial descent from ZBW 370 to 330 due to turbulence. After a short delay we received clearance to FL330, this clearance came just as I was leaving my seat (first officer) to make a quick trip to the lavatory. I responded to the center radio call, cleared to FL330, on the hand microphone, having just removed my headset. Captain set the altitude select window to 330, which I verified with him. Captain at same time made a change to vertical speed selector to select 1000 FPM descent rate. This selection, however, must have been to a +1.0 not -1.0 on vertical speed select. I did not observe the actual setting since I was just leaving my seat. When I returned and sat down, ZBW asked if we copied the clearance to 330 and expedite descent. I looked at altitude selected on pfd altitude window and saw 330 was indeed selected but we were now at 37.7 and climbing. We quickly selected an 'open descent' and went down to 330, ZBW never commented on our actual altitude as conflicting with traffic. I did notice a 1.0 indicated in vertical speed window, but was not sure of the plus or minus indication. I felt this would not have occurred if I were fully 'in the loop'. Supplemental information from acn 139485: sun was shining on the glass cover of vertical speed window and had a bad glare. I checked FMA that vertical speed was displayed, then was distracted by something else. The next time I looked at the altitude we were at FL337 in a slight climb. I had set in a plus instead of negative value.

Original NASA ASRS Text

Title: ALT DEVIATION. EXCURSION FROM ASSIGNED.

Narrative: REQUESTED INITIAL DSCNT FROM ZBW 370 TO 330 DUE TO TURBULENCE. AFTER A SHORT DELAY WE RECEIVED CLRNC TO FL330, THIS CLRNC CAME JUST AS I WAS LEAVING MY SEAT (F/O) TO MAKE A QUICK TRIP TO THE LAVATORY. I RESPONDED TO THE CENTER RADIO CALL, CLRED TO FL330, ON THE HAND MICROPHONE, HAVING JUST REMOVED MY HEADSET. CAPT SET THE ALT SELECT WINDOW TO 330, WHICH I VERIFIED WITH HIM. CAPT AT SAME TIME MADE A CHANGE TO VERTICAL SPEED SELECTOR TO SELECT 1000 FPM DSCNT RATE. THIS SELECTION, HOWEVER, MUST HAVE BEEN TO A +1.0 NOT -1.0 ON VERTICAL SPEED SELECT. I DID NOT OBSERVE THE ACTUAL SETTING SINCE I WAS JUST LEAVING MY SEAT. WHEN I RETURNED AND SAT DOWN, ZBW ASKED IF WE COPIED THE CLRNC TO 330 AND EXPEDITE DSCNT. I LOOKED AT ALT SELECTED ON PFD ALT WINDOW AND SAW 330 WAS INDEED SELECTED BUT WE WERE NOW AT 37.7 AND CLIMBING. WE QUICKLY SELECTED AN 'OPEN DSCNT' AND WENT DOWN TO 330, ZBW NEVER COMMENTED ON OUR ACTUAL ALT AS CONFLICTING WITH TFC. I DID NOTICE A 1.0 INDICATED IN VERTICAL SPEED WINDOW, BUT WAS NOT SURE OF THE PLUS OR MINUS INDICATION. I FELT THIS WOULD NOT HAVE OCCURRED IF I WERE FULLY 'IN THE LOOP'. SUPPLEMENTAL INFORMATION FROM ACN 139485: SUN WAS SHINING ON THE GLASS COVER OF VERTICAL SPEED WINDOW AND HAD A BAD GLARE. I CHECKED FMA THAT VERTICAL SPEED WAS DISPLAYED, THEN WAS DISTRACTED BY SOMETHING ELSE. THE NEXT TIME I LOOKED AT THE ALT WE WERE AT FL337 IN A SLIGHT CLIMB. I HAD SET IN A PLUS INSTEAD OF NEGATIVE VALUE.

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.