Narrative:

We were flying IFR from tucson, az, to tijuana, baja ca. In our flight plan we filed for FL390. ZAB cleared us to FL350 and told us that he would take us to FL390, west from gbn. Approximately 15 mi west from gbn he gave us a clearance to climb to FL370 and that later he would clear us to FL390. The first officer acknowledged that we had understood and that at the moment we were starting to climb to FL370, to which the controller didn't say anything. When we reached FL370, we reported to the center that we were leveling at FL370, and we got no response from the center. After approximately 4 mins we reported to center again that we were at FL370 to which the controller answered that we should descend and maintain FL350. We started the descent and then the controller indicated us to turn 30 degrees anyway. We got to FL350 and after a while we were cleared to FL390. When ZAB switched us to ZLA, he told us that we had to call ZAB by phone # in relation to the events that occurred near gbn. I called ZAB and he told me that there was a report in which the controller had given us some traffic information, to which we, in his opinion, had understood it as a clearance. On the recorded tape at that moment communication was bad and it is not possible to understand our readback in which we said that we were climbing to FL370. They reported that the closest point to another aircraft was 3 1/2 mi and 800'. Apparently the problem comes to a failure in the reception in the center, since when we acknowledged and read back, upon having no answer from center to our readback, we understood our readback was correct. Readbacks are as important as clrncs are, because their purpose is to let the controller know if there was any misunderstanding in his clearance, so he then has a chance to correct it.

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Original NASA ASRS Text

Title: CPR LTT ALT DEVIATION EXCURSION FROM CLRNC ALT.

Narrative: WE WERE FLYING IFR FROM TUCSON, AZ, TO TIJUANA, BAJA CA. IN OUR FLT PLAN WE FILED FOR FL390. ZAB CLRED US TO FL350 AND TOLD US THAT HE WOULD TAKE US TO FL390, W FROM GBN. APPROX 15 MI W FROM GBN HE GAVE US A CLRNC TO CLB TO FL370 AND THAT LATER HE WOULD CLR US TO FL390. THE F/O ACKNOWLEDGED THAT WE HAD UNDERSTOOD AND THAT AT THE MOMENT WE WERE STARTING TO CLB TO FL370, TO WHICH THE CTLR DIDN'T SAY ANYTHING. WHEN WE REACHED FL370, WE RPTED TO THE CENTER THAT WE WERE LEVELING AT FL370, AND WE GOT NO RESPONSE FROM THE CENTER. AFTER APPROX 4 MINS WE RPTED TO CENTER AGAIN THAT WE WERE AT FL370 TO WHICH THE CTLR ANSWERED THAT WE SHOULD DSND AND MAINTAIN FL350. WE STARTED THE DSCNT AND THEN THE CTLR INDICATED US TO TURN 30 DEGS ANYWAY. WE GOT TO FL350 AND AFTER A WHILE WE WERE CLRED TO FL390. WHEN ZAB SWITCHED US TO ZLA, HE TOLD US THAT WE HAD TO CALL ZAB BY PHONE # IN RELATION TO THE EVENTS THAT OCCURRED NEAR GBN. I CALLED ZAB AND HE TOLD ME THAT THERE WAS A RPT IN WHICH THE CTLR HAD GIVEN US SOME TFC INFO, TO WHICH WE, IN HIS OPINION, HAD UNDERSTOOD IT AS A CLRNC. ON THE RECORDED TAPE AT THAT MOMENT COM WAS BAD AND IT IS NOT POSSIBLE TO UNDERSTAND OUR READBACK IN WHICH WE SAID THAT WE WERE CLBING TO FL370. THEY RPTED THAT THE CLOSEST POINT TO ANOTHER ACFT WAS 3 1/2 MI AND 800'. APPARENTLY THE PROB COMES TO A FAILURE IN THE RECEPTION IN THE CENTER, SINCE WHEN WE ACKNOWLEDGED AND READ BACK, UPON HAVING NO ANSWER FROM CENTER TO OUR READBACK, WE UNDERSTOOD OUR READBACK WAS CORRECT. READBACKS ARE AS IMPORTANT AS CLRNCS ARE, BECAUSE THEIR PURPOSE IS TO LET THE CTLR KNOW IF THERE WAS ANY MISUNDERSTANDING IN HIS CLRNC, SO HE THEN HAS A CHANCE TO CORRECT IT.

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.