B757-200 crew had a double map shift while flying the dylin 2 STAR into ewr.

Attributes
ACN	569575
Time
Date	200212
Day	Mon
Place
Locale Reference	airport : ewr.airport
State Reference	NJ
Altitude	msl bound lower : 8000 msl bound upper : 11000
Aircraft 1
Controlling Facilities	tracon : n90.tracon
Operator	common carrier : air carrier
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent : vacating altitude
Route In Use	arrival star : dylin
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	569575
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : multi engine
ASRS Report	570069
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : published procedure non adherence : company policies other anomaly other other spatial deviation
Independent Detector	other flight crewa other flight crewb
Resolutory Action	none taken : detected after the fact other
Consequence	other
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Double map shift. On descent to ewr on the dylin 2 arrival, first officer crossed somto intersection at 11000 ft. He was descending precisely to make the crossing altitudes. He continued the descent to cross dylin at 8000 ft. Around yardley, we were at 8500 ft and descending to cross dylin at 8000 ft when we experienced a sudden map shift. This shift caused somto to appear in front of us. First officer disconnected the autoplt and started a climb to 11000 ft. The map shifted again because somto and dylin suddenly appeared behind us and we missed the dylin 8000 ft by 800 ft because of the climb first officer started to 11000 ft. We were instructed by ATC to turn to a 020 degree heading at mersr and may have missed that turn a little due to the map shift. By the time we reverted to raw data, the map appeared to be normal. ATC said nothing. The remainder of the flight was normal. First officer had the airplane descending perfectly for the arrival so when the shifts occurred, I am reasonably sure that we made the xings and heading assignment regardless of the map shifts. I have never seen this type of shift X2 along the path and would not have believed it possible if I had not seen it myself.

Original NASA ASRS Text

Title: B757-200 CREW HAD A DOUBLE MAP SHIFT WHILE FLYING THE DYLIN 2 STAR INTO EWR.

Narrative: DOUBLE MAP SHIFT. ON DSCNT TO EWR ON THE DYLIN 2 ARR, FO CROSSED SOMTO INTXN AT 11000 FT. HE WAS DSNDING PRECISELY TO MAKE THE XING ALTS. HE CONTINUED THE DSCNT TO CROSS DYLIN AT 8000 FT. AROUND YARDLEY, WE WERE AT 8500 FT AND DSNDING TO CROSS DYLIN AT 8000 FT WHEN WE EXPERIENCED A SUDDEN MAP SHIFT. THIS SHIFT CAUSED SOMTO TO APPEAR IN FRONT OF US. FO DISCONNECTED THE AUTOPLT AND STARTED A CLB TO 11000 FT. THE MAP SHIFTED AGAIN BECAUSE SOMTO AND DYLIN SUDDENLY APPEARED BEHIND US AND WE MISSED THE DYLIN 8000 FT BY 800 FT BECAUSE OF THE CLB FO STARTED TO 11000 FT. WE WERE INSTRUCTED BY ATC TO TURN TO A 020 DEG HDG AT MERSR AND MAY HAVE MISSED THAT TURN A LITTLE DUE TO THE MAP SHIFT. BY THE TIME WE REVERTED TO RAW DATA, THE MAP APPEARED TO BE NORMAL. ATC SAID NOTHING. THE REMAINDER OF THE FLT WAS NORMAL. FO HAD THE AIRPLANE DSNDING PERFECTLY FOR THE ARR SO WHEN THE SHIFTS OCCURRED, I AM REASONABLY SURE THAT WE MADE THE XINGS AND HDG ASSIGNMENT REGARDLESS OF THE MAP SHIFTS. I HAVE NEVER SEEN THIS TYPE OF SHIFT X2 ALONG THE PATH AND WOULD NOT HAVE BELIEVED IT POSSIBLE IF I HAD NOT SEEN IT MYSELF.

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.