A B722 crew misinterped clearance and descended out of assigned altitude.

Attributes
ACN	501820
Time
Date	200102
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : sfb.airport
State Reference	FL
Altitude	msl bound lower : 3000 msl bound upper : 4000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : mco.tracon
Operator	common carrier : air carrier
Make Model Name	B727-200
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude
Route In Use	arrival : on vectors
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : mco.tracon
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise : level
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : instrument pilot : multi engine pilot : atp
Experience	flight time last 90 days : 120 flight time total : 2500 flight time type : 1700
ASRS Report	501820
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued alert flight crew : returned to assigned altitude
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

The aircraft was level at 4000 ft MSL. We were told that there was traffic at 3000 ft MSL moving north (from right to left), and to expect lower after clearing this traffic. That traffic was pointed out one more time at 11 O'clock position moving away, and we received what we thought was a clearance to descend to 3000 ft MSL. Approaching 3000 ft, orl approach control told us that they did not clear us to 3000 ft and told us to return to 4000 ft. All altitudes were acknowledged by us.

Original NASA ASRS Text

Title: A B722 CREW MISINTERPED CLRNC AND DSNDED OUT OF ASSIGNED ALT.

Narrative: THE ACFT WAS LEVEL AT 4000 FT MSL. WE WERE TOLD THAT THERE WAS TFC AT 3000 FT MSL MOVING N (FROM R TO L), AND TO EXPECT LOWER AFTER CLRING THIS TFC. THAT TFC WAS POINTED OUT ONE MORE TIME AT 11 O'CLOCK POS MOVING AWAY, AND WE RECEIVED WHAT WE THOUGHT WAS A CLRNC TO DSND TO 3000 FT MSL. APCHING 3000 FT, ORL APCH CTL TOLD US THAT THEY DID NOT CLR US TO 3000 FT AND TOLD US TO RETURN TO 4000 FT. ALL ALTS WERE ACKNOWLEDGED BY US.

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.