Date: 201907
Local time of day: 0001-0600
Location: DCA.Airport, DC
Flight conditions: VMC
Aircraft: A320
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B DCA
ATC / advisory: TRACON PCT
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Communication Breakdown; Situational Awareness
Second reporter function: Pilot Not Flying; First Officer
Anomaly: ATC Issue All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Clearance
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: While approaching DCA the weather began dropping making both advertised approaches to Runway 19 and 15 unlikely options. I contacted Dispatch via ACARS requesting possible coordination with ATC to land on Runway 1 with a small tailwind. I checked landing performance data for both Runway 19; 15 and 1. Runway 15 would be very tight at 5;195 feet (5;204 length) using auto brakes 2. Runway 19 left us with more margin; but 25 feet less on minimums. Runway 15 had its PAPI NOTAMed out as well. While Dispatch worked with ATC we briefed the TRUPS4 Arrival and LDA-Z 19 as I felt it was the safest course of action and advertised as available. When we checked on with Potomac Approach; they advised us to expect RNAV (GPS) 15 and after 'FRDMM; fly heading 120. I asked the First Officer to request ILS 1; as the latest at ATIS had the WX at 700 BKN and below minimums for both 19 and 15. Approach advised a small delay would be in order; but expect ILS 1. I asked the First Officer to load ILS 1 in the FMC; while I pulled it up on my Jeppesen Pro X. When loading the transition for ILS 1 the FMC drops the north side transition (Runway 19) and loads the south transition for Runway 1. 'FRDMM' is replaced by 'LETZZ' as the North and South transitions diverge at 'TRUPS.' Our last clearance was to fly 120 heading at 'FRDMM;' which was no longer on our transition. As we crossed 'TRUPS' I began to fly the transition for Runway 1; while the First Officer queried ATC if they would like us to fly 120 heading at 'LETZZ' now instead. ATC advised to just fly the north transition. Initially this terminology was confusing and I asked the First Officer to clarify what he meant; 'The north Runway 1 transition or the North segment of the transition.' ATC confirmed the Runway 1 transition. While it seemed to go as well as could be expected; we were told to 'Expect' Runway 1; but not actually cleared to fly that transition until clarifying while joining it. We caught it very early and I estimate we were within 1-1.5 miles of the track either way. We continued inbound and made an eventful approach and landing to Runway 1. During our flight debrief I became a point of discussion and felt it best to report the situation. The workload was high at the time and ATC was also very busy; so it added to the complexity of communicating. In the end; I believe we were doing what ATC expected; but may not have been cleared for the south (Runway 1 transition) when he advised 'expect Runway 1'.


Second narrative: [Report narrative contained no additional information.]


Synopsis: A320 pilots reported a track heading deviation during approach to DCA airport.  Communication problems with ATC on which transition to fly were cited as contributing factors.