Date: 201705
Local time of day: 1201-1800
Location: PCT.TRACON, MD
Light: Daylight
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
Airspace: Class B BWI
ATC / advisory: TRACON PCT
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: Pilot Flying; First Officer
Anomaly: Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Returned To Clearance
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: This was our second day together as a Crew.  We had flown two legs on this day prior to a planned aircraft swap for our last leg of the day.  We received a normal 'as filed' clearance through CPDLC and completed Captain's and PF (Pilot Flying) Briefings.  At scheduled push time and just prior to receiving the loadsheet from the Agent; we received a new clearance from CPDLC 'cleared route clearance +load new route to ZZZ+'.  The new route contained the same SID and transition as the original clearance.  We both observed as the new route was loaded and confirmed that the reverse video portion showed the amended routing correctly prior to accepting and executing the new route.  Since the new routing did not change the original and already loaded SID and transition; we did not re-brief the departure and I think (but am not completely sure) the SID was still loaded correctly.At that point; I called Dispatch to report the new routing and amend the Release with the increased time and fuel burn- approximately 15 minutes and 1;000 pounds; while the F/O (First Officer) continued with his duties.  Pushback and engine start were normal. As we turned on to Taxiway U; we could see no one was ahead of us so I rang the F/As (Flight Attendants) to announce takeoff clearance.  It took nearly a minute for the F/As to make their PA and allow us to continue with the Before Takeoff Checklist. We were quickly cleared to 'line up and wait' and we watched as a small single engine aircraft cleared to land on 33R and continued to proceed down final for our runway (Runway 28). At about the time I stopped the aircraft short of Runway 28 and the F/O queried the Tower Controller; the small aircraft banked abruptly to align with 33L. The result of these two events; the delay from F/As; and the concern over landing runway with the small aircraft was that I got out of my habit pattern of checking the F/O's CDU and selecting an appropriate page for my CDU.  In this case; the F/O had the Takeoff page; so I would have normally had the LEGS page selected. I also normally scan the FMA to insure that autopilot and LNAV are armed.  In this case; I am not sure I accomplished that scan.I transferred control of the aircraft to the F/O and we were cleared for takeoff. Autothrottles worked normally and takeoff was normal until shortly after liftoff.  The Tower Controller apologized for the confusion with the small aircraft as he switched us to Departure and the F/O noted that the flight director switches were off.  As we contacted Departure and retracted flaps on speed; the F/O turned on the flight director switches and reselected TO/GA. Departure Control asked if we were on the TERPZ Departure and when I saw that WONCE was not on the LEGS page I requested radar vectors.  Departure Control issued a vector.  The aircraft was not responding as the F/O wanted so he disengaged the autopilot and turned to the heading while I attempted to load the CDU.  ATC then issued direct WONCE and the departure. I tried to load WONCE into the LEGS page but it immediately dropped out.  At this point I noticed the FMA showed 'arm' for the autothrottle.  I relayed to ATC and we were cleared direct TERPZ.  I was able to load TERPZ; we proceeded direct and were then cleared 'TERPZ and then OTTTO'.  I asked if she wanted us to proceed to FOXHL and then OTTTO after TERPZ (the OTTTO transition) and ATC replied 'Negative. TERPZ then OTTTO'.  We were then switched to another Departure Control frequency.  He asked about our routing since we were not following the filed transition and I replied that the previous Controller had cleared us from TERPZ direct to OTTTO.This is the first time I have received a second clearance thru CPDLC right at push time; after having completely briefed the original clearance. I know it is a documented problem that SIDs and transitions on amended clearances do not load with the rest of the clearance; but in this case the SID and transition were the samein both clearances and we had already loaded and briefed the SID. I thought- and I'm still not sure that it didn't- the SID that was previously loaded would remain. In hindsight; I would be completely sure that the SID and transition were properly loaded and that I would not allow multiple distractions to take me out of my habit pattern of having one CDU on the legs page to insure we were flying the SID correctly.


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


Synopsis: B737-800 Crew reported the SID dropped out after they received a new clearance from CPDLC and did not discover that until they were airborne.