Captain reported a navigation error due to similar sounding STAR names.

Attributes
ACN	1747213
Time
Date	202006
Local Time Of Day	1201-1800
Place
Locale Reference	ZDV.ARTCC
State Reference	CO
Aircraft 1
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Route In Use	Direct STAR AALLE 1
Flight Plan	IFR
Person 1
Function	Captain
Qualification	Flight Crew Instrument Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine
Events
Anomaly	ATC Issue All Types Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Deviation - Track / Heading All Types

Narrative:

We were assigned the aalle 1 RNAV arrival into den. We heard denver center clear us direct to flail and to descend via the aalle 1 arrival into denver and that's what the first officer read back to ATC without them questioning us. He programmed that into the FMC and I confirmed it; then set 11;000 feet in the MCP for the lowest altitude. A few minutes later ATC queried where we were going as he showed us off course and we should have been going to aalle instead. The first officer re-programmed that into the FMC and I confirmed it. 11;000 was still a good lowest altitude and the flight path vector showed us not to our top of descent yet so we were on path. I'm not sure ATC knows how to pronounce aalle properly because the way he said it; it sounded like flail. Both aalle and flail sound very similar; especially when you are in a loud cockpit. The waypoint flail needs to be changed on the aalle 1 RNAV arrival because aalle and flail sound way too similar. Especially when you are in a loud cockpit.

Original NASA ASRS Text

Title: Captain reported a navigation error due to similar sounding STAR names.

Narrative: We were assigned the AALLE 1 RNAV arrival into DEN. We heard Denver Center clear us direct to FLAIL and to descend via the AALLE 1 arrival into Denver and that's what the First Officer read back to ATC without them questioning us. He programmed that into the FMC and I confirmed it; then set 11;000 feet in the MCP for the lowest altitude. A few minutes later ATC queried where we were going as he showed us off course and we should have been going to AALLE instead. The First Officer re-programmed that into the FMC and I confirmed it. 11;000 was still a good lowest altitude and the flight path vector showed us not to our top of descent yet so we were on path. I'm not sure ATC knows how to pronounce AALLE properly because the way he said it; it sounded like FLAIL. Both AALLE and FLAIL sound very similar; especially when you are in a loud cockpit. The waypoint FLAIL needs to be changed on the AALLE 1 RNAV Arrival because AALLE and FLAIL sound way too similar. Especially when you are in a loud cockpit.

Data retrieved from NASA's ASRS site 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.