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.
Synopsis
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.
Second reporter narrative
During cruise flight at FL350 as First Officer was on a restroom break; Center cleared our flight to FL330. First Officer returned a short time later. I then informed him that we were now level at FL330 and then made a restroom break myself. While in the bathroom I felt the aircraft had started a descent and assumed the descent was for a FL240 arrival crossing restriction. After returning to the flight deck we were at FL310. The First Officer then said the aircraft had descended toward FL300 which he said was in the altitude select window when he got back into the seat. I was then puzzled because I know I had descended to FL330 while he was gone to the restroom. As we were switched to the next Controller we were then given a contact number. After the flight I then called the contact number and talked to the Operations Manager. He said Flight xxx responded to a clearance for another flight and the matter had been taken care of due to the fact that the Controller on duty had not corrected the mistake. Be more thorough on briefing the other pilot when returning to the flight deck and ensure that he acknowledges it.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.