ZLA Center Controller and an air carrier Pilot reported an altitude deviation due to a read back error while on the KARLB2 arrival to ONT. The Controller and Pilot both stated similar sounding fix names GOATZ and COAZT contributed to the event.
Synopsis
ZLA Center Controller and an air carrier Pilot reported an altitude deviation due to a read back error while on the KARLB2 arrival to ONT. The Controller and Pilot both stated similar sounding fix names GOATZ and COAZT contributed to the event.
Narrative
I was at D25 & 28. Air Carrier X checked in from the ocean and was issued the proper squawk code. Shortly after; my R side radar identified him issued revised routing to provided a shortcut; via direct GOATZ for the KARLB2 arrival to ONT. The pilot read it back and it sounded correct. Later on; Air Carrier X was issued cross GOATZ at and maintain 16;000 feet. Pilot also read back and it sounded correct.The issue presented itself later on when I noticed it appeared Air Carrier X was off course and I brought it to my R side's attention. After questioning the pilot; it turned out he navigated direct to COAZT which is a fix further down the arrival. After fixing the route he would not be able to meet the crossing restriction at GOATZ as he was still level at FL390 when this took place. Therefore Air Carrier X had to be vectored around in order to have enough space to descend.While safety was not compromised in this specific situation; if traffic was different this could have been a major problem caused by something so simple as two-way points with extremely similar names. I recommend that COAZT should be renamed to something different to prevent the confusion with GOATZ. GOATZ is used for many other things so it should stay the same; and the KARLB arrival should be updated.
Second reporter narrative
Operating Air Carrier X; ZZZ to ONT. Checked in with Center at FL390. We were given our squawk code; radar contact; and a descent clearance to cross what we heard as; and read back COAZT at 16;000. We selected the appropriate altitude; confirmed VNAV was selected and continued on. After a few minutes ATC came back and asked if we were still direct COAZT. We read back COAZT and spelled it back for him phonetically. It was then that he corrected us and read back GOATZ at 16;000. The Controller asked if we would be able to meet that crossing restriction; or if we'd need a vector to get down. After finding the fix on the STAR; we requested a turn so we'd be able to make the crossing. We were then turned back in to sequence for the remainder of the arrival. The very similar spelling of the fixes on a single arrival is confusing. Depending volume of radio traffic; and the pronunciation of an awkward word during a high work load; they are easily mistaken as both the Controller and the crew did today.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.