Air carrier flight crew reported track and altitude deviations occurred on approach to bna following...

Attributes
ACN	1753769
Time
Date	202007
Local Time Of Day	1201-1800
Place
Locale Reference	BNA.TRACON
State Reference	TN
Aircraft 1
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Person 1
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 10 Flight Crew Type 18000
Person 2
Function	Pilot Not Flying First Officer
Experience	Flight Crew Last 90 Days 84
Events
Anomaly	Conflict Airborne Conflict Deviation - Altitude Excursion From Assigned Altitude Deviation - Altitude Overshoot Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Inflight Event / Encounter Weather / Turbulence

Narrative:

I was the captain and pilot flying. We checked on with bna approach and said we would like the RNAV Z to 20R. We were told unable and expect the ILS 20R and descend to 10;000'. I deviated for weather then [was] told to descend via the arrival. Shortly before sippo; I was told that I was cleared the RNAV Z for 20R. Since I had the ILS loaded after the heading on the arrival; this caused some confusion. Both pilots went heads down trying to figure this out. I saw a VNAV disconnect message on the CDU. The aircraft started a left turn and a shallow descent to about 4800' and I was supposed to be at 5000'. I got a TCAS warning to level off for a small aircraft beneath me. I followed the HUD indications until I was 'clear of conflict '. By the time we entered the RNAV approach; we were inside of sippo and headed to the next point. The rest of the approach was in VMC and uneventful. We were given a phone number to call by ground control entering our gate area.I should not have accepted the RNAV approach so close to the IAF. I should have said unable and continued on the ILS.

Original NASA ASRS Text

Title: Air carrier flight crew reported track and altitude deviations occurred on approach to BNA following a late change in approach procedure. Lack of recent flying experience was cited as contributing.

Narrative: I was the Captain and Pilot Flying. We checked on with BNA Approach and said we would like the RNAV Z to 20R. We were told unable and expect the ILS 20R and descend to 10;000'. I deviated for weather then [was] told to descend via the arrival. Shortly before SIPPO; I was told that I was cleared the RNAV Z for 20R. Since I had the ILS loaded after the heading on the arrival; this caused some confusion. Both pilots went heads down trying to figure this out. I saw a VNAV DISCONNECT message on the CDU. The aircraft started a left turn and a shallow descent to about 4800' and I was supposed to be at 5000'. I got a TCAS warning to level off for a small aircraft beneath me. I followed the HUD indications until I was 'Clear of Conflict '. By the time we entered the RNAV approach; we were inside of SIPPO and headed to the next point. The rest of the approach was in VMC and uneventful. We were given a phone number to call by Ground Control entering our gate area.I should not have accepted the RNAV approach so close to the IAF. I should have said unable and continued on the ILS.

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.

Air carrier flight crew reported track and altitude deviations occurred on approach to bna following a late change in approach procedure. Lack of recent flying experience was cited as contributing.