Date: 202007
Local time of day: 1201-1800
Location: BNA.TRACON, TN
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
ATC / advisory: TRACON BNA
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Time Pressure; Situational Awareness
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew; Person Air Traffic Control
When detected: In-flight
Result: Flight Crew Became Reoriented; Flight Crew Returned To Clearance; Flight Crew Took Evasive Action
Contributing factors: Human Factors
Primary problem: Human Factors

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.


Second narrative: We were coming into BNA on the SWFFT 2 Arrival. When handed off to BNA we were given clearance to 'descend via; deviate as needed for weather just be back on course by SIPPO.' ATC said to expect vectors ILS 20R. PM; F/O; then asked if RNAV Z 20R at SIPPO was available. ATC said 'possibly; but not likely'. PF; Captain; then made certain ILS 20R was loaded. Crew had briefed both approaches and we were hopeful that we would get the RNAV to land quicker. There was no pressure to land early just trying to get the flight done quickly. Just prior to HAKUM; second to last point of STAR; ATC cleared us for RNAV approach. Late clearance resulted in high workload for PF who wanted to do it himself. PF started to input new approach. After selecting the approach and feeder fix PF pushed the Execute button. On the LEGS page it had direct HAKUM; then a disconnect. Following the disconnect there was HAKUM and SIPPO for the rest of the STAR with a heading then disconnect. After that was the RNAV. PF became task saturated trying to link the approach at SIPPO. PM offered to fix the box. PF wanted more practice due to the lack of recent flying in the past five months; first trip for PF in that time frame. PM's situational awareness was taken watching the PF correct the box due to prior errors made during the trip. However; once we hit HAKUM the aircraft kept descending as VNAV disconnected then went through the at or above 5000' and started a left turn back to HAKUM. PM noticed the VNAV disconnect and mentioned it to the PF but did no other intervention. PM and PF noticed the left turn when it should be a right turn to SIPPO. Roll mode disengaged as well at this time. But PF was trying to fly and not knowing autopilot had no inputs but last things commanded. PF at that point asked PM to link the box. PM corrected the box. ATC called and said we missed our turn and asked if we needed vectors back to SIPPO. PM said no after PF said it was good now with the box while he manually pointed towards WOKAP. PF went direct WOKAP. During the turn back to WOKAP the PF only rolled the aircraft and did not see descent. Task load made it so he did not know aircraft was over 1000' low. PM knew aircraft was low; but due to workload monitoring the PF with the FMC; PM forgot the altitude clearance limit. In the process of looking up the altitude; PM saw traffic below and called it out. ATC called out traffic as well. RA occurred with general aviation aircraft. PF was slow to get the aircraft climbing again. PM mentioned need to climb. PF only claimed till out of RA; and not back to clearance altitude. PM called out the need to climb back to 5000'. Don't know if we ever got back to cleared altitude. Scariest part was PF was heads down trying to manually fly and do the box all the while not realizing the rapid rate of descent. At some point PM thought no one was flying the aircraft but CWS pitch and roll; which took the aircraft out of how it was supposed to be flown. Nose low recovery was really slow.With late clearance changes or then in the terminal area and PF needs/wants to manipulate the FMC aircraft control should be handed to other Pilot. PM watched the event occur but should have taken control of aircraft once altitude deviation occurred. PM should have been more directive.


Synopsis: 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.