B737-800
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 311; Flight Crew Type 8500
Aircraft Equipment Problem Critical; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Flight Crew Diverted; Flight Crew Landed As Precaution
Aircraft
During climbout we experienced a complete loss of navigation capability. Both NAV DUs stopped displaying course/waypoint information. Shortly thereafter; both FO and Captain DISPLY SOURCE flags appeared. Seconds later the Captain's SPD LIM flap appeared. QRH was consulted and run twice; offering no resolution. Circuit breakers were checked and none were tripped. During the QRH procedure; the FO (PF) noticed the throttles began to split by approximately two inches; while the N1s remained constant at climb thrust. Within 10 to 15 seconds; the autothrottle system disconnected and could not be re-engaged. We elected to level off at FL280 (below RVSM) and a vector was requested. Via AIRINC; we contacted Dispatch and MX Control. With their guidance we attempted to troubleshoot the problem but nothing appeared to help. During one suggestion from MX Control (selecting the displays switch to BOTH ON L); all five upper DUs went completely black. Once AUTO was reselected; on the displays switch; the DUs came back but still had the above mentioned flags. It was at this time the Dispatcher and I agreed to divert. VFR weather; long runways; pilot familiarity and Company MX drove the decision to divert. In addition; we were 15000 pounds above max landing weight. We received a vector to [divert airport]; and given a lower cruise altitude. As we approached the airport; we held for approximately 20 minutes in a close-in vectored box pattern away from inbound traffic; as we burned off the excess fuel. A subsequent uneventful landing was made. PAs to the passengers were made every 10 - 15 minutes explaining what we were doing and why. I kept the explanation simple and concise; yet timely; hopefully offering a high level of reassurance. I spoke to our Flight Attendants; and gave them a more detailed explanation; and kept them seated as a precaution.A situation like this is hardly predictable. Mx Control and Dispatch asked us twice if we were 'OK to continue' (I was assuming to our destination) and my answer both times was NO. No navigation; DU issues; at night; into downline weather wasn't a situation I was interested in exploring.
B737-800 Captain reported diverting to an alternate after loss of all navigation capability during climbout.