Narrative:

We had a normal takeoff and I called for LNAV at 400 ft. The pm could not engage it after several attempts. The flight directors disappeared. The HSI did not provide course guidance even though the HSI selectors were set up for LNAV prior to takeoff. Because of the navigation errors; we missed the immediate turn to sapee on the wevic 4 SID. The frequency was busy; the pm and I were trying to solve the navigation issue and still retract the flaps when the controller asked if we were following the RNAV SID. We told the controller we were unable RNAV and obtained the vector. When the pm tried to line select a fix; the FMC did not respond on the right but I was finally able to select a fix on the left FMC. We received clearance direct musaw and the LNAV and VNAV worked properly for the remainder of the flight. I believe this navigation error occurred because the route wasn't activated and executed on the ground prior to takeoff. I didn't see evidence of this problem on the ground when I looked at the route pages or legs pages during my preflight and briefings. Additionally; in hindsight; I would have tried to tell ATC that we were unable RNAV sooner since the initial turn is immediate. But we had to fly the aircraft first and then communicate. Thankfully; we didn't forget to retract the flaps in the climb as we were trying to problem solve.

Related reports:

Google
 

Original NASA ASRS Text

Title: B737 flight crew reported being unable to use LNAV after takeoff from SLC. A vector was requested from ATC and once cleared direct to MUSAW the FMC and LNAV returned to normal operation.

Narrative: We had a normal takeoff and I called for LNAV at 400 ft. The PM could not engage it after several attempts. The flight directors disappeared. The HSI did not provide course guidance even though the HSI selectors were set up for LNAV prior to takeoff. Because of the navigation errors; we missed the immediate turn to SAPEE on the WEVIC 4 SID. The frequency was busy; the PM and I were trying to solve the navigation issue and still retract the flaps when the Controller asked if we were following the RNAV SID. We told the controller we were unable RNAV and obtained the vector. When the PM tried to line select a fix; the FMC did not respond on the right but I was finally able to select a fix on the left FMC. We received clearance direct MUSAW and the LNAV and VNAV worked properly for the remainder of the flight. I believe this navigation error occurred because the route wasn't activated and executed on the ground prior to takeoff. I didn't see evidence of this problem on the ground when I looked at the Route pages or LEGS pages during my preflight and briefings. Additionally; in hindsight; I would have tried to tell ATC that we were unable RNAV sooner since the initial turn is immediate. But we had to fly the aircraft first and then communicate. Thankfully; we didn't forget to retract the flaps in the climb as we were trying to problem solve.

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.