KC135E crew descended to 4000 ft. The controller meant for them to descend to 5000 ft.

Attributes
ACN	511285
Time
Date	200105
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : acy.airport
State Reference	NJ
Altitude	msl bound lower : 4000 msl bound upper : 5000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : acy.tracon
Operator	other
Make Model Name	Stratotanker 135
Navigation In Use	other
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	government : military
Function	flight crew : first officer
Qualification	pilot : military pilot : flight engineer pilot : commercial pilot : atp pilot : multi engine
Experience	flight time last 90 days : 100 flight time total : 3700 flight time type : 3400
ASRS Report	511285
Person 2
Affiliation	government : military
Function	flight crew : captain oversight : pic
Events
Anomaly	altitude deviation : overshoot non adherence : published procedure other anomaly other
Independent Detector	atc equipment other atc equipment : radar other controllera
Resolutory Action	controller : issued new clearance controller : issued alert none taken : detected after the fact
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance

Narrative:

We were descending out of 8000 ft while we were being controled by acy approach control. We were cleared to 4000 ft and I acknowledged the clearance to 4000 ft and we descended to and leveled at 4000 ft. After cruising at 4000 ft for at least 5 mins, the controller asked us what altitude we were cleared to. We stated 4000 ft. He said 'no, 5000 ft was the clearance,' and we had traffic at 12 O'clock that had us in sight. Once the traffic was clear, we were cleared to descend to 3000 ft. Another crew member confirmed he heard 4000 ft and watched me set 4000 ft in the altitude alerter. I believe the controller intended us to be at 5000 ft, but stated 4000 ft. Most of the time we transit this area, we are cleared to 5000 ft. The 'break in the chain' occurred when I repeated back to him, 'cleared to 4000 ft' and he did not catch the mistake. We never came close enough to any other traffic for TCASII to activate. No other comments were made by the ATC controller.

Original NASA ASRS Text

Title: KC135E CREW DSNDED TO 4000 FT. THE CTLR MEANT FOR THEM TO DSND TO 5000 FT.

Narrative: WE WERE DSNDING OUT OF 8000 FT WHILE WE WERE BEING CTLED BY ACY APCH CTL. WE WERE CLRED TO 4000 FT AND I ACKNOWLEDGED THE CLRNC TO 4000 FT AND WE DSNDED TO AND LEVELED AT 4000 FT. AFTER CRUISING AT 4000 FT FOR AT LEAST 5 MINS, THE CTLR ASKED US WHAT ALT WE WERE CLRED TO. WE STATED 4000 FT. HE SAID 'NO, 5000 FT WAS THE CLRNC,' AND WE HAD TFC AT 12 O'CLOCK THAT HAD US IN SIGHT. ONCE THE TFC WAS CLR, WE WERE CLRED TO DSND TO 3000 FT. ANOTHER CREW MEMBER CONFIRMED HE HEARD 4000 FT AND WATCHED ME SET 4000 FT IN THE ALT ALERTER. I BELIEVE THE CTLR INTENDED US TO BE AT 5000 FT, BUT STATED 4000 FT. MOST OF THE TIME WE TRANSIT THIS AREA, WE ARE CLRED TO 5000 FT. THE 'BREAK IN THE CHAIN' OCCURRED WHEN I REPEATED BACK TO HIM, 'CLRED TO 4000 FT' AND HE DID NOT CATCH THE MISTAKE. WE NEVER CAME CLOSE ENOUGH TO ANY OTHER TFC FOR TCASII TO ACTIVATE. NO OTHER COMMENTS WERE MADE BY THE ATC CTLR.

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.