Air carrier flight at FL335 with ZTL; experienced near loss of separation during descent; anticipati...

Attributes
ACN	826492
Time
Date	200903
Local Time Of Day	1801-2400
Place
Locale Reference	MTU.VORTAC
State Reference	UT
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Route In Use	STAR LEEHY
Flight Plan	IFR
Aircraft 2
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Person 1
Function	Pilot Flying First Officer
Qualification	Flight Crew Flight Instructor Flight Crew Instrument Flight Crew Multiengine Flight Crew Flight Engineer Flight Crew Commercial Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 210 Flight Crew Total 9400 Flight Crew Type 4500
Events
Anomaly	Conflict Airborne Conflict
Miss Distance	Horizontal 1000

Narrative:

While in cruise at FL360; ZLC (135.77) cleared us down to FL340. I reset the altitude window and both the captain and I pointed to the window to verify the correct altitude. I started to descend and almost immediately thereafter ATC cleared us down to FL300. Again; the altitude window was set and both the captain and I verified the correct setting in the window. At approximately FL335; ATC called and told us to maintain FL340. We stated that we were already below that altitude and were told to climb and maintain FL340. ATC next called air carrier Y. I could tell by the controller's voice and instructions to the air carrier Y flight that we were about to have a traffic conflict. I elected to disconnect the autopilot to immediately initiate the climb. ATC then told us to turn right to 300 degrees. While in the turn; we received a TCAS TA. Once past the air carrier Y flight; we were cleared direct to the mtu VOR to resume the leehy arrival into ZLC. We were told that ATC had already reviewed the tapes; that they (ATC) were at fault; and that separation had not been lost between the 2 aircraft.

Original NASA ASRS Text

Title: Air carrier flight at FL335 with ZTL; experienced near loss of separation during descent; anticipating a Controller error; the reporter started a climb that saved legal separation.

Narrative: While in cruise at FL360; ZLC (135.77) cleared us down to FL340. I reset the altitude window and both the Captain and I pointed to the window to verify the correct altitude. I started to descend and almost immediately thereafter ATC cleared us down to FL300. Again; the altitude window was set and both the Captain and I verified the correct setting in the window. At approximately FL335; ATC called and told us to maintain FL340. We stated that we were already below that altitude and were told to climb and maintain FL340. ATC next called Air Carrier Y. I could tell by the Controller's voice and instructions to the Air Carrier Y flight that we were about to have a traffic conflict. I elected to disconnect the autopilot to immediately initiate the climb. ATC then told us to turn right to 300 degrees. While in the turn; we received a TCAS TA. Once past the Air Carrier Y flight; we were cleared direct to the MTU VOR to resume the LEEHY arrival into ZLC. We were told that ATC had already reviewed the tapes; that they (ATC) were at fault; and that separation had not been lost between the 2 aircraft.

Data retrieved from NASA's ASRS site as of April 2012 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.

Air carrier flight at FL335 with ZTL; experienced near loss of separation during descent; anticipating a controller error; the reporter started a climb that saved legal separation.