Flight crew of an mdt responded to another aircraft's clearance and descended before it was time!

Attributes
ACN	308380
Time
Date	199506
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : dxo airport : dtw
State Reference	MI
Altitude	msl bound lower : 10500 msl bound upper : 11000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : lga
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	enroute : on vectors enroute airway : dtw
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : commercial pilot : instrument
Experience	flight time last 90 days : 240 flight time total : 7000 flight time type : 2800
ASRS Report	308380
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	other controllera
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

While talking to dtw approach, we were instructed to descend to 4000 ft MSL, and change frequencys to the final approach controller. I read back: descend to 4000 ft, contact approach on 124.05. The controller said 'affirmative.' I switched frequencys, and the captain began our descent. There was no reply on the new frequency, I switched back to the previous one and told the controller we could not raise anyone on the other frequency. He said, 'the descent, and frequency change was for another aircraft, climb back up to 11000 ft.' we were at 10500 ft MSL. We stopped our descent, and climbed back to 11000 ft MSL without any further incident.

Original NASA ASRS Text

Title: FLC OF AN MDT RESPONDED TO ANOTHER ACFT'S CLRNC AND DSNDED BEFORE IT WAS TIME!

Narrative: WHILE TALKING TO DTW APCH, WE WERE INSTRUCTED TO DSND TO 4000 FT MSL, AND CHANGE FREQS TO THE FINAL APCH CTLR. I READ BACK: DSND TO 4000 FT, CONTACT APCH ON 124.05. THE CTLR SAID 'AFFIRMATIVE.' I SWITCHED FREQS, AND THE CAPT BEGAN OUR DSCNT. THERE WAS NO REPLY ON THE NEW FREQ, I SWITCHED BACK TO THE PREVIOUS ONE AND TOLD THE CTLR WE COULD NOT RAISE ANYONE ON THE OTHER FREQ. HE SAID, 'THE DSCNT, AND FREQ CHANGE WAS FOR ANOTHER ACFT, CLB BACK UP TO 11000 FT.' WE WERE AT 10500 FT MSL. WE STOPPED OUR DSCNT, AND CLBED BACK TO 11000 FT MSL WITHOUT ANY FURTHER INCIDENT.

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.