B737-300 crew descended below the charted altitude restr on the dylin 1 into ewr.

Attributes
ACN	543549
Time
Date	200204
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : dqo.vortac
State Reference	DE
Altitude	msl single value : 21000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc.artcc artcc : zny.artcc
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : approach
Route In Use	arrival star : dylin 1
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 180 flight time total : 10000 flight time type : 7000
ASRS Report	543549
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	altitude deviation : crossing restriction not met altitude deviation : overshoot non adherence : published procedure non adherence : company policies non adherence : far non adherence : clearance
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : overrode automation none taken : detected after the fact other
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Flying to ewr, I was given clearance for the profile descent (the dylin 1 arrival). Even though I had seen this type profile yrs ago flying into lax, this is the first one I had actually flown in quite some time. I put 8000 ft in the altitude window which is the restr at dylin. At the time, we were southwest of dupont. At the time the clearance was received, we were at FL250. As I customarily do, I selected the descent page on the FMC to monitor the vertical speed required to meet any altitude restr. As opposed to waiting for an idle descent, I normally will initiate the descent prior to the vertical speed requiring 2000 FPM by selecting the capture mode. This mode selects 1000 FPM descent until the aircraft intercepts an idle descent glide path where upon the thrust levers retard to idle and the autoplt initiates the idle descent. After accomplishing this task, I started to brief the approach to runway 9L in accordance with company policy. My attention was diverted while doing so, and I did not realize that the aircraft had descended below the at or above restr at dqo which was FL220. Approaching FL210, the VNAV mode disengaged giving a warning light which drew the captain's attention and we discovered the deviation. I immediately stopped the descent manually and corrected to altitude. We were probably 4-5 DME southwest of dqo at the time. Initially, both the captain and I were unsure with why the automation, with the restrs entered into the FMC, did not comply with the profile descent. The more I thought about it, the more I realized if I had let the aircraft descend at the selected idle descent point instead of using the capture mode, the problem would have been avoided. In addition, with a profile descent clearance being somewhat out of the ordinary for me, I should not have allowed myself to be distraction briefing the approach without ensuring the automation was actually complying with the published altitude restr on the arrival. I admittedly was probably too complacent feeling comfortable with the FMC and doing something I normally do on dscnts without considering how this one was a little different from what I have been accustomed to.

Original NASA ASRS Text

Title: B737-300 CREW DSNDED BELOW THE CHARTED ALT RESTR ON THE DYLIN 1 INTO EWR.

Narrative: FLYING TO EWR, I WAS GIVEN CLRNC FOR THE PROFILE DSCNT (THE DYLIN 1 ARR). EVEN THOUGH I HAD SEEN THIS TYPE PROFILE YRS AGO FLYING INTO LAX, THIS IS THE FIRST ONE I HAD ACTUALLY FLOWN IN QUITE SOME TIME. I PUT 8000 FT IN THE ALT WINDOW WHICH IS THE RESTR AT DYLIN. AT THE TIME, WE WERE SW OF DUPONT. AT THE TIME THE CLRNC WAS RECEIVED, WE WERE AT FL250. AS I CUSTOMARILY DO, I SELECTED THE DSCNT PAGE ON THE FMC TO MONITOR THE VERT SPD REQUIRED TO MEET ANY ALT RESTR. AS OPPOSED TO WAITING FOR AN IDLE DSCNT, I NORMALLY WILL INITIATE THE DSCNT PRIOR TO THE VERT SPD REQUIRING 2000 FPM BY SELECTING THE CAPTURE MODE. THIS MODE SELECTS 1000 FPM DSCNT UNTIL THE ACFT INTERCEPTS AN IDLE DSCNT GLIDE PATH WHERE UPON THE THRUST LEVERS RETARD TO IDLE AND THE AUTOPLT INITIATES THE IDLE DSCNT. AFTER ACCOMPLISHING THIS TASK, I STARTED TO BRIEF THE APCH TO RWY 9L IN ACCORDANCE WITH COMPANY POLICY. MY ATTN WAS DIVERTED WHILE DOING SO, AND I DID NOT REALIZE THAT THE ACFT HAD DSNDED BELOW THE AT OR ABOVE RESTR AT DQO WHICH WAS FL220. APCHING FL210, THE VNAV MODE DISENGAGED GIVING A WARNING LIGHT WHICH DREW THE CAPT'S ATTN AND WE DISCOVERED THE DEV. I IMMEDIATELY STOPPED THE DSCNT MANUALLY AND CORRECTED TO ALT. WE WERE PROBABLY 4-5 DME SW OF DQO AT THE TIME. INITIALLY, BOTH THE CAPT AND I WERE UNSURE WITH WHY THE AUTOMATION, WITH THE RESTRS ENTERED INTO THE FMC, DID NOT COMPLY WITH THE PROFILE DSCNT. THE MORE I THOUGHT ABOUT IT, THE MORE I REALIZED IF I HAD LET THE ACFT DSND AT THE SELECTED IDLE DSCNT POINT INSTEAD OF USING THE CAPTURE MODE, THE PROB WOULD HAVE BEEN AVOIDED. IN ADDITION, WITH A PROFILE DSCNT CLRNC BEING SOMEWHAT OUT OF THE ORDINARY FOR ME, I SHOULD NOT HAVE ALLOWED MYSELF TO BE DISTR BRIEFING THE APCH WITHOUT ENSURING THE AUTOMATION WAS ACTUALLY COMPLYING WITH THE PUBLISHED ALT RESTR ON THE ARR. I ADMITTEDLY WAS PROBABLY TOO COMPLACENT FEELING COMFORTABLE WITH THE FMC AND DOING SOMETHING I NORMALLY DO ON DSCNTS WITHOUT CONSIDERING HOW THIS ONE WAS A LITTLE DIFFERENT FROM WHAT I HAVE BEEN ACCUSTOMED TO.

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.