Narrative:

Departing runway 18L on the RNAV departure; I was the pilot flying. Uneventful liftoff and rotation into the flight director command bars. At 400 ft AGL I called for LNAV. The pilot not flying selected LNAV on the MCP and I verified LNAV on the AFDS. I noticed a slight right bank of the flight director. I assumed I had drifted slightly left due to a right crosswind and the flight director was correcting so I stayed in the command bars. At the appropriate acceleration altitude we set climb thrust and began accelerating to 220 KTS. ATC then told us to make an immediate 20 degree left turn. The flight director then commanded a left turn and I continued to stay tight in the command bars and executed the left turn assuming the pilot not flying had selected heading and set the heading. I attempted to activate the paddle B autopilot but the aircraft must have been out of trim and it would not engage so I continued to hand fly the aircraft. The AFDS was still showing LNAV not heading that I had assumed the pilot not flying had engaged because of the ATC clearance. ATC then queried the heading we were flying as we had turned more than the 20 degrees left as instructed. I was still following the flight director with LNAV selected on the MCP and verified on the AFDS. ATC then cleared us direct to an intersection on the RNAV departure. The pilot not flying selected; verified and executed the waypoint into the FMC. I verified his actions and that LNAV was still active and selected. I again attempted to activate the autopilot but I could not engage it. I continued to hand fly the aircraft and stayed in the flight director at all times. The pilot not flying then asked me where I was going. I responded that I was direct the intersection. He then took control of the aircraft and manually turned it correctly. We cleared the flight directors and then reengaged them. Activated the autopilot and LNAV and navigated uneventfully to our destination. The day following the event in question; I flew aircraft the same 737-300 that was part of the previous report. During the flight to our destination and back the captain experienced anomalies in the aircraft's FMC particularly with waypoints. He noted that he had never seen this type of issue. There were also slight anomalies with the flight directors but none of significance like the day prior. I can not understand why the flight director was giving erroneous information but by blindly following it caused the situation I found myself in. By blindly following the commanded bars I created self induced tunnel vision and lost situational awareness. The route was verified at the gate and the departure legs and waypoints were confirmed as well but relying solely on the automation and maybe not using cami to its full usefulness contributed to my error. On takeoff; cross checking the aircraft's heading would have revealed a problem right away. I self assured myself that verifying LNAV on the AFDS and staying in the flight director would keep me where I am suppose to be. A wrong assumption; when ATC gave us the immediate turn that should have been an eye opener that my situational awareness was in the yellow and cross checked my heading and assured the heading was selected in the MCP and that we were indeed turning 20 degrees left and not follow a flight director giving poor information. Had that been done the situation would have ended then and there. Fighting with the autopilot paddle was an added distraction that contributed to the situation. The captain and I debriefed after landing. After listening to his assessment of the situation it became clear that he was unaware of my flight director difficulties and autopilot distraction. What he witnessed and what I witnessed we're two different events even though we were in the same cockpit. This all came about because lack of communication in the cockpit. I was on the right and he was on the left. We never communicated to each other what we were seeing and never crosschecked to see what was happening on the other side. As the problem arose I should have started talking right then. I did state a couple of times that we're in LNAV and that I was just following the command bars but I never spoke up and asserted myself and asked him what he was seeing or saying we have a problem here. By not giving him a clear picture of what I was seeing he was not able to communicate to me the information I needed. Neither of us crosschecked or communicated to the other what they were seeing. After realizing a problem existed; a crosscheck and open communication would have stopped the error and got us back on course.

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Original NASA ASRS Text

Title: A non-GPS B737-300 had a track deviation after takeoff on a RNAV departure after the Flight Director gave an incorrect turn command.

Narrative: Departing Runway 18L on the RNAV Departure; I was the pilot flying. Uneventful liftoff and rotation into the flight director command bars. At 400 FT AGL I called for LNAV. The pilot not flying selected LNAV on the MCP and I verified LNAV on the AFDS. I noticed a slight right bank of the flight director. I assumed I had drifted slightly left due to a right crosswind and the flight director was correcting so I stayed in the command bars. At the appropriate acceleration altitude we set climb thrust and began accelerating to 220 KTS. ATC then told us to make an immediate 20 degree left turn. The flight director then commanded a left turn and I continued to stay tight in the command bars and executed the left turn assuming the pilot not flying had selected HDG and set the heading. I attempted to activate the paddle B autopilot but the aircraft must have been out of trim and it would not engage so I continued to hand fly the aircraft. The AFDS was still showing LNAV not HDG that I had assumed the pilot not flying had engaged because of the ATC clearance. ATC then queried the heading we were flying as we had turned more than the 20 degrees left as instructed. I was still following the flight director with LNAV selected on the MCP and verified on the AFDS. ATC then cleared us direct to an intersection on the RNAV Departure. The pilot not flying selected; verified and executed the waypoint into the FMC. I verified his actions and that LNAV was still active and selected. I again attempted to activate the autopilot but I could not engage it. I continued to hand fly the aircraft and stayed in the flight director at all times. The pilot not flying then asked me where I was going. I responded that I was direct the intersection. He then took control of the aircraft and manually turned it correctly. We cleared the flight directors and then reengaged them. Activated the autopilot and LNAV and navigated uneventfully to our destination. The day following the event in question; I flew aircraft the same 737-300 that was part of the previous report. During the flight to our destination and back the Captain experienced anomalies in the aircraft's FMC particularly with waypoints. He noted that he had never seen this type of issue. There were also slight anomalies with the flight directors but none of significance like the day prior. I can not understand why the flight director was giving erroneous information but by blindly following it caused the situation I found myself in. By blindly following the commanded bars I created self induced tunnel vision and lost situational awareness. The route was verified at the gate and the departure legs and waypoints were confirmed as well but relying solely on the automation and maybe not using CAMI to its full usefulness contributed to my error. On takeoff; cross checking the aircraft's heading would have revealed a problem right away. I self assured myself that verifying LNAV on the AFDS and staying in the flight director would keep me where I am suppose to be. A wrong assumption; when ATC gave us the immediate turn that should have been an eye opener that my situational awareness was in the yellow and cross checked my heading and assured the HDG was selected in the MCP and that we were indeed turning 20 degrees left and not follow a flight director giving poor information. Had that been done the situation would have ended then and there. Fighting with the autopilot paddle was an added distraction that contributed to the situation. The Captain and I debriefed after landing. After listening to his assessment of the situation it became clear that he was unaware of my flight director difficulties and autopilot distraction. What he witnessed and what I witnessed we're two different events even though we were in the same cockpit. This all came about because lack of communication in the cockpit. I was on the right and he was on the left. We never communicated to each other what we were seeing and never crosschecked to see what was happening on the other side. As the problem arose I should have started talking right then. I did state a couple of times that we're in LNAV and that I was just following the command bars but I never spoke up and asserted myself and asked him what he was seeing or saying we have a problem here. By not giving him a clear picture of what I was seeing he was not able to communicate to me the information I needed. Neither of us crosschecked or communicated to the other what they were seeing. After realizing a problem existed; a crosscheck and open communication would have stopped the error and got us back on course.

Data retrieved from NASA's ASRS site as of July 2013 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.