Narrative:

Captain was pilot flying (PF) and I was pilot monitoring (pm). We were being vectored for RNAV xxl. The captain flew through the final approach course two times. The third time around the RNAV xxl approach was completed successfully.first time around; PF did not activate his approach on his FMS. While on heading mode (heading 150 degrees); ATC instructed to intercept final approach course; PF selected navigation mode and the plane wanted to fly to the first outer fix.ATC then called back noticing that we had flown through the final approach course; ATC vectored us around for the approach again. I ask the PF to arm the approach in his FMS and not select navigation mode until the CDI was alive and two dots from intercepting the course. I also mentioned that if he selected the navigation mode and the plane began to do something else than what we wanted; I suggested him to deactivate the autopilot and hand fly.once on approach the second time; being vectored to intercept navigation mode was selected again and the plane turned in the opposite direction than what we were instructed to fly. ATC canceled approach clearance and vectored us away from a third try.on the third try; I requested that we get cleared direct to the fix before the final approach fix that way the FMS would sequence properly.if not being cleared direct to a fix on a RNAV approach on the [type of aircraft we were flying]; ensure the approach is activated and be ready to hand fly if needed.

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Original NASA ASRS Text

Title: EMB-140 First Officer reported flying through final approach course due to non-activation approach mode. After third attempt; PF became re-oriented and executed approach.

Narrative: Captain was Pilot Flying (PF) and I was Pilot Monitoring (PM). We were being vectored for RNAV XXL. The Captain flew through the final approach course two times. The third time around the RNAV XXL approach was completed successfully.First time around; PF did not activate his approach on his FMS. While on heading mode (heading 150 degrees); ATC instructed to intercept final approach course; PF selected NAV mode and the plane wanted to fly to the first outer fix.ATC then called back noticing that we had flown through the final approach course; ATC vectored us around for the approach again. I ask the PF to arm the approach in his FMS and not select NAV mode until the CDI was alive and two dots from intercepting the course. I also mentioned that if he selected the NAV mode and the plane began to do something else than what we wanted; I suggested him to deactivate the autopilot and hand fly.Once on approach the second time; being vectored to intercept NAV mode was selected again and the plane turned in the opposite direction than what we were instructed to fly. ATC canceled approach clearance and vectored us away from a third try.On the third try; I requested that we get cleared direct to the fix before the final approach fix that way the FMS would sequence properly.If not being cleared direct to a fix on a RNAV approach on the [type of aircraft we were flying]; ensure the approach is activated and be ready to hand fly if needed.

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.