B747-400
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Situational Awareness
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Wake Vortex Encounter
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors; Environment - Non Weather Related
We were departing out of ANC; with myself as Captain and Pilot Flying; on a clearance to fly the KNIK 2 departure from Runway 07L. High temp operations that day with many aircraft cleared for takeoff with short spacing. We briefed; as one of our threats; to not turn in the wrong direction for the SID. We briefed that the last three departures I had done off Runway 07L were initially with a clearance to fly the KNIK 2 departure then cancelled upon taking the runway and given a heading to fly on departure. Once cleared for takeoff we verbalized the fact that we had direct gusting crosswinds and to also be vigilant about possible wake turbulence from a B748 that departed moments before us. After liftoff; we corrected for an increase in wind and wake turbulence we encountered that was pushing us of left of centerline. As the aircraft settled; I scrolled out my ND scale for better terrain situational awareness and upon doing so; I believed we were much closer to the turn point for the SID. I called for heading select with a left turn to a heading 329. It took the Pilot Monitoring a bit to select the heading and we visually cleared the area and began the turn. ATC asked us to expedite our climb through 4;000 feet. Rest of departure had no incidents and at top of climb ATC gave us a number to call when we got back on the ground about a possible deviation. We realized we had turned early on the SID despite following procedures by conducting a pre-departure brief and covering all pertinent items. I believe my conformation bias about receiving headings to fly at departure on previous flights; in conjunction with the movement in scale of my PFD lead me to call for the turn too early. No other crew members caught this issue and at no time was there a safety or terrain issue as expressed to me by the ANC Controller I spoke with upon our arrival. There is no excuse for this type of error as our procedure; when done correctly; should mitigate these threats. The crew discussed this in great detail afterwards and each had suggestions for going forward in the safest way possible. For myself; I plan to add as a threat for any flight any possible conformation bias based on previous flights. Also; I believe I should set my scale once prior to departure and leave it there as long as the first way-point is in view. Moving the scale again gave me a false sense of distance to the turn point and I failed to recognize I might be turning too early.
B747-400 Captain reported a track deviation occurred departing ANC.