Air carrier descends below assigned altitude. Has TCASII alert.

Attributes
ACN	196278
Time
Date	199112
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : mxe
State Reference	PA
Altitude	msl bound lower : 14500 msl bound upper : 18000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Large Transport
Flight Phase	descent other
Route In Use	enroute airway : zny
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 25000
ASRS Report	196278
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	altitude deviation : overshoot altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

On descent into bwi we were given a crossing restriction 15 northeast of mxe VOR. 15000 ft was set and crosschecked by both pilots. I, as captain, noted after leveling off, '18' written on my note pad. ATC made no comment and turned us over to next sector. This controller asked for repeat of altitude which we did confirm as 15000 ft. 5 mins later ATC called traffic 12 O'clock climbing 15 to 16. This traffic was climbing slow because it set off TCASII for us to descend which we did and advised ATC who cleared us to 12000 ft. We had traffic in sight and could see no serious problem. ATC overloaded system needs to be backed off a little.

Original NASA ASRS Text

Title: ACR DSNDS BELOW ASSIGNED ALT. HAS TCASII ALERT.

Narrative: ON DSCNT INTO BWI WE WERE GIVEN A XING RESTRICTION 15 NE OF MXE VOR. 15000 FT WAS SET AND XCHKED BY BOTH PLTS. I, AS CAPT, NOTED AFTER LEVELING OFF, '18' WRITTEN ON MY NOTE PAD. ATC MADE NO COMMENT AND TURNED US OVER TO NEXT SECTOR. THIS CTLR ASKED FOR REPEAT OF ALT WHICH WE DID CONFIRM AS 15000 FT. 5 MINS LATER ATC CALLED TFC 12 O'CLOCK CLBING 15 TO 16. THIS TFC WAS CLBING SLOW BECAUSE IT SET OFF TCASII FOR US TO DSND WHICH WE DID AND ADVISED ATC WHO CLRED US TO 12000 FT. WE HAD TFC IN SIGHT AND COULD SEE NO SERIOUS PROBLEM. ATC OVERLOADED SYS NEEDS TO BE BACKED OFF A LITTLE.

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.