Narrative:

Our clearance was an RNAV; departure; zzzzz transition. The first officer and I conducted a normal aircraft preflight. As the flying pilot; I entered the RNAV/FMS procedure/transition/expected departure runway; along with our route of flight. The first officer and I then reviewed the SID with our flight plan and legs page. All points; bearings; and dmes were in agreement. During the taxi out; both pilots verified that both navigation switches were in the correct position; navigation. Both FD switches were confirmed on. After we were cleared for takeoff; the first officer accomplished a position update; as we took the runway. I confirmed his actions. On the line up for takeoff; we confirmed that our HSI course arrows were centered and pointed on an initial heading to the first fix. After takeoff and at 400 ft; I called 'left navigation.' at this time the first officer activated the left navigation function. I confirmed his action by the left navigation indication on the FMA. I began to fly the command bars of the ADI. The command bars initially commanded a slight left bank to correct on course. At this time we were in night IMC conditions; with a non-EFIS aircraft. Without any visual points of reference; I continued to follow the command bars; thinking that we were encountering a strong crosswind. I stated this to the first officer. The HSI course arrow indicated that we were still on course. Tower instructed us to contact departure control. The first officer was in the process of performing his 'after takeoff' activities and contacting departure control; when I brought to his attention that the command bars were calling for an even greater bank to remain on course. I did not believe that we were receiving correct navigation information; so I rolled wings level. I then noticed a route discontinuity on my legs page of the FMC. The route discontinuity was not indicated during our preflight route check or on the line up for takeoff check. I started a turn back to the right. The first officer stated that he was going to notify ATC of our problem; when departure control instructed us to turn right; to be vectored back on course. I believe that due to time compression and a high work load factor; along with this problem; delayed us from notifying ATC earlier. We rejoined the departure. Our flight continued without any other problems. Upon arrival; I contacted the controlling manager for the departure control. He stated that there was no conflicting traffic with our departure; but he was going to have to report the incident.callback conversation with reporter revealed the following information: reporter stipulated the disadvantages of the lack of a moving map display to provide overall situational awareness in a single place. He emphasized that once LNAV was commanded and engaged his attention was concentrated on the command bars of the flight director which should have provided guidance toward the initial fix on the SID. What ultimately caused him to abandon the command bars was the realization that the HSI fpdi was displaying the deviation caused by the faulty commands. Finally; the realization that there was a route discontinuity came only upon review of the legs page of the FMS CDU mounted on the pedestal forward of the throttles. He advised there is no indication of a route discontinuity on the HSI or the flight director displays. Thus; full realization of the extent of their situation required examination and diagnosis of at least three separate indicators. Reporter further advised that he was aware of other similar anomalies and suggested that the lack of a moving map display was a large contributing factor to such events becoming potentially hazardous through a delay in recognition of the evolving situation.

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Original NASA ASRS Text

Title: Non-EFIS; non-GPS equipped B737 suffered a track deviation on an RNAV SID. Appears to have been the result of a route discontinuity that was not observed during the preflight route verification.

Narrative: Our clearance was an RNAV; Departure; ZZZZZ Transition. The First Officer and I conducted a normal aircraft preflight. As the flying pilot; I entered the RNAV/FMS procedure/transition/expected departure runway; along with our route of flight. The First Officer and I then reviewed the SID with our flight plan and legs page. All points; bearings; and DMEs were in agreement. During the taxi out; both pilots verified that both Navigation switches were in the correct position; NAV. Both FD switches were confirmed on. After we were cleared for takeoff; the First Officer accomplished a position update; as we took the runway. I confirmed his actions. On the line up for takeoff; we confirmed that our HSI course arrows were centered and pointed on an initial heading to the first fix. After takeoff and at 400 FT; I called 'L NAV.' At this time the First Officer activated the L NAV function. I confirmed his action by the L NAV indication on the FMA. I began to fly the command bars of the ADI. The command bars initially commanded a slight left bank to correct on course. At this time we were in night IMC conditions; with a non-EFIS aircraft. Without any visual points of reference; I continued to follow the command bars; thinking that we were encountering a strong crosswind. I stated this to the First Officer. The HSI course arrow indicated that we were still on course. Tower instructed us to contact departure control. The First Officer was in the process of performing his 'after takeoff' activities and contacting departure control; when I brought to his attention that the command bars were calling for an even greater bank to remain on course. I did not believe that we were receiving correct navigation information; so I rolled wings level. I then noticed a route discontinuity on my legs page of the FMC. The route discontinuity was not indicated during our preflight route check or on the line up for takeoff check. I started a turn back to the right. The First Officer stated that he was going to notify ATC of our problem; when departure control instructed us to turn right; to be vectored back on course. I believe that due to time compression and a high work load factor; along with this problem; delayed us from notifying ATC earlier. We rejoined the departure. Our flight continued without any other problems. Upon arrival; I contacted the controlling manager for the departure control. He stated that there was no conflicting traffic with our departure; but he was going to have to report the incident.Callback conversation with reporter revealed the following information: Reporter stipulated the disadvantages of the lack of a moving map display to provide overall situational awareness in a single place. He emphasized that once LNAV was commanded and engaged his attention was concentrated on the command bars of the flight director which should have provided guidance toward the initial fix on the SID. What ultimately caused him to abandon the command bars was the realization that the HSI FPDI was displaying the deviation caused by the faulty commands. Finally; the realization that there was a route discontinuity came only upon review of the legs page of the FMS CDU mounted on the pedestal forward of the throttles. He advised there is no indication of a route discontinuity on the HSI or the flight director displays. Thus; full realization of the extent of their situation required examination and diagnosis of at least three separate indicators. Reporter further advised that he was aware of other similar anomalies and suggested that the lack of a moving map display was a large contributing factor to such events becoming potentially hazardous through a delay in recognition of the evolving situation.

Data retrieved from NASA's ASRS site as of April 2012 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.