An air carrier crew reported that they mistakenly took a company flights descent clearance and ackno...

Narrative:

During cruise at FL350; prior to descent; captain and I coordinated with the cabin crew to go back to the restroom. As I was getting out of the seat; with my headphones off; captain got a clearance from ATC to descend to FL330 and he read back the clearance and noted the altitude change to me as I was leaving the cockpit. When I returned and took my seat; captain reported to me that we had been cleared to FL300. I saw that we were already in a descent; passing through FL327; and that the altitude select window was set at FL300. As we descended through FL318; ATC called me with an urgent request to descend to FL310. I responded and moved the altitude select window up from FL300 to FL310; while retarding the throttles further. Shortly thereafter I confirmed with ATC that they wanted us at FL310 and they replied affirmative. The controller was flustered and I thought she had made some sort of mistake. There was another aircraft very close to us on the TCAS. Approximately 5 minutes later we were given a number to call and told it was in reference to a possible violation. When we got on the ground; captain called the ATC manager's number that we had been given and we were told that there was no violation. The ATC manger confirmed that we had read back a clearance to FL300. Apparently; just prior to my returning to the cockpit; captain had read back a clearance for another flight to descend to FL300. The controller did not correct his read back; and so we had no way of knowing that the clearance was not for us. We followed all of the required procedures during this event. However; I will say that I have seen a trend for the exchange of command to be rushed during bathroom breaks. I was in my seat and buckled before captain got up; but it was a hurried exchange; and the rush was probably a factor in the miscommunication between captain and ATC.

Original NASA ASRS Text

Title: An air carrier crew reported that they mistakenly took a Company flights descent clearance and acknowledged it to ATC. ATC did not correct the error and during descent were given an expedited descent clearance because of traffic.

Narrative: During cruise at FL350; prior to descent; Captain and I coordinated with the cabin crew to go back to the restroom. As I was getting out of the seat; with my headphones off; Captain got a clearance from ATC to descend to FL330 and he read back the clearance and noted the altitude change to me as I was leaving the cockpit. When I returned and took my seat; Captain reported to me that we had been cleared to FL300. I saw that we were already in a descent; passing through FL327; and that the altitude select window was set at FL300. As we descended through FL318; ATC called me with an urgent request to descend to FL310. I responded and moved the altitude select window up from FL300 to FL310; while retarding the throttles further. Shortly thereafter I confirmed with ATC that they wanted us at FL310 and they replied affirmative. The Controller was flustered and I thought she had made some sort of mistake. There was another aircraft very close to us on the TCAS. Approximately 5 minutes later we were given a number to call and told it was in reference to a possible violation. When we got on the ground; Captain called the ATC manager's number that we had been given and we were told that there was no violation. The ATC manger confirmed that we had read back a clearance to FL300. Apparently; just prior to my returning to the cockpit; Captain had read back a clearance for another flight to descend to FL300. The Controller did not correct his read back; and so we had no way of knowing that the clearance was not for us. We followed all of the required procedures during this event. However; I will say that I have seen a trend for the exchange of command to be rushed during bathroom breaks. I was in my seat and buckled before Captain got up; but it was a hurried exchange; and the rush was probably a factor in the miscommunication between Captain and ATC.

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.

Attributes
ACN	909841
Time
Date	201009
Local Time Of Day	1201-1800
Place
Locale Reference	ZAU.ARTCC
State Reference	IL
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Medium Large Transport Low Wing 2 Turbojet Eng
Operating Under FAR Part	Part 121
Flight Phase	Cruise Descent
Flight Plan	IFR
Person 1
Function	Pilot Not Flying First Officer
Person 2
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	ATC Issue All Types Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy

An air carrier crew reported that they mistakenly took a company flights descent clearance and acknowledged it to ATC. ATC did not correct the error and during descent were given an expedited descent clearance because of traffic.