B737 crew had crossing altitude restr not met.

Attributes
ACN	447365
Time
Date	199908
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : sie.vortac
State Reference	NJ
Altitude	msl bound lower : 35000 msl bound upper : 35500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc.artcc
Operator	common carrier : air carrier
Make Model Name	B737-400
Operating Under FAR Part	Part 121
Navigation In Use	other other vortac
Flight Phase	descent : vacating altitude
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zdc.artcc
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 255 flight time total : 18000 flight time type : 16000
ASRS Report	447365
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	altitude deviation : crossing restriction not met conflict : airborne critical non adherence : clearance non adherence : required legal separation
Independent Detector	other controllera
Resolutory Action	controller : separated traffic controller : issued new clearance
Miss Distance	horizontal : 15000 vertical : 1500
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance ATC Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Flight was proceeding direct sie (sea isle) at FL370 when directed by ATC to cross 25 mi south of sie at and maintain FL350. My first officer and I heard the clearance as 25 mi south sie at FL250. I (captain, PNF) repeated the clearance as I heard it...'25 mi south sie at FL250.' since there was no correcting response from ATC, the first officer (PF) initiated a rapid descent to FL250...the crossing restr was very close so a 4000 FPM descent was necessary. Passing approximately FL360-FL355, I decided we would not make the crossing restr at FL250 and notified ATC. ATC responded with an amended clearance to simply maintain FL350. The first officer immediately initiated a climb back to FL350, but the aircraft had already descended through FL350. The controller mentioned, after this event, in a casual voice, that we may have had a loss of separation with another aircraft. This surprised us as we got no RA or TA, or vectors from ATC. After our next frequency change, we were informed of the 'loss of separation' officially. I believe this situation would have been avoided if the controller had responded with the correct clearance since we obviously misunderstood the clearance.

Original NASA ASRS Text

Title: B737 CREW HAD XING ALT RESTR NOT MET.

Narrative: FLT WAS PROCEEDING DIRECT SIE (SEA ISLE) AT FL370 WHEN DIRECTED BY ATC TO CROSS 25 MI S OF SIE AT AND MAINTAIN FL350. MY FO AND I HEARD THE CLRNC AS 25 MI S SIE AT FL250. I (CAPT, PNF) REPEATED THE CLRNC AS I HEARD IT...'25 MI S SIE AT FL250.' SINCE THERE WAS NO CORRECTING RESPONSE FROM ATC, THE FO (PF) INITIATED A RAPID DSCNT TO FL250...THE XING RESTR WAS VERY CLOSE SO A 4000 FPM DSCNT WAS NECESSARY. PASSING APPROX FL360-FL355, I DECIDED WE WOULD NOT MAKE THE XING RESTR AT FL250 AND NOTIFIED ATC. ATC RESPONDED WITH AN AMENDED CLRNC TO SIMPLY MAINTAIN FL350. THE FO IMMEDIATELY INITIATED A CLB BACK TO FL350, BUT THE ACFT HAD ALREADY DSNDED THROUGH FL350. THE CTLR MENTIONED, AFTER THIS EVENT, IN A CASUAL VOICE, THAT WE MAY HAVE HAD A LOSS OF SEPARATION WITH ANOTHER ACFT. THIS SURPRISED US AS WE GOT NO RA OR TA, OR VECTORS FROM ATC. AFTER OUR NEXT FREQ CHANGE, WE WERE INFORMED OF THE 'LOSS OF SEPARATION' OFFICIALLY. I BELIEVE THIS SIT WOULD HAVE BEEN AVOIDED IF THE CTLR HAD RESPONDED WITH THE CORRECT CLRNC SINCE WE OBVIOUSLY MISUNDERSTOOD THE CLRNC.

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.