Air carrier descended by ATC to an altitude occupied by another aircraft.

Attributes
ACN	103761
Time
Date	198902
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : pie
State Reference	FL
Altitude	msl bound lower : 11700 msl bound upper : 13000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zjx
Operator	common carrier : air carrier
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	descent other
Route In Use	enroute : direct enroute airway : zjx
Flight Plan	IFR
Aircraft 2
Operator	other
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 200
ASRS Report	103761
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : overshoot conflict : airborne less severe non adherence : published procedure non adherence : required legal separation non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Miss Distance	horizontal : 4000 vertical : 700
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

To the best of my knowledge we were descending to cross 35 miles out of st pete at 13000', when we received a clearance to continue descent to 11000'. I acknowledged the clearance to 11000'. There was no response to my acknowledgement indicating an error. Sometime later, approximately one to three minutes, while we were approaching 35 at 13000', we were turned over to the next controller. He immediately notified us to stop descending. He pointed out the traffic in conflict, a military jet. We had visual contact with the aircraft. The controller then cleared us back up to 13000'. As you know! We are unable to hear UHF military radios. This may have been a contributing factor. Our response to the clearance may have been blocked by the UHF military reply without any indication to us. No correction of my acknowledgement indicated the readback was ok!

Original NASA ASRS Text

Title: ACR DESCENDED BY ATC TO AN ALT OCCUPIED BY ANOTHER ACFT.

Narrative: TO THE BEST OF MY KNOWLEDGE WE WERE DSNDING TO CROSS 35 MILES OUT OF ST PETE AT 13000', WHEN WE RECEIVED A CLRNC TO CONTINUE DSCNT TO 11000'. I ACKNOWLEDGED THE CLRNC TO 11000'. THERE WAS NO RESPONSE TO MY ACKNOWLEDGEMENT INDICATING AN ERROR. SOMETIME LATER, APPROXIMATELY ONE TO THREE MINUTES, WHILE WE WERE APCHING 35 AT 13000', WE WERE TURNED OVER TO THE NEXT CTLR. HE IMMEDIATELY NOTIFIED US TO STOP DSNDING. HE POINTED OUT THE TFC IN CONFLICT, A MIL JET. WE HAD VISUAL CONTACT WITH THE ACFT. THE CTLR THEN CLRED US BACK UP TO 13000'. AS YOU KNOW! WE ARE UNABLE TO HEAR UHF MIL RADIOS. THIS MAY HAVE BEEN A CONTRIBUTING FACTOR. OUR RESPONSE TO THE CLRNC MAY HAVE BEEN BLOCKED BY THE UHF MIL REPLY WITHOUT ANY INDICATION TO US. NO CORRECTION OF MY ACKNOWLEDGEMENT INDICATED THE READBACK WAS OK!

Data retrieved from NASA's ASRS site as of August 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.