B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 148; Flight Crew Type 10000
Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude
Air Traffic Control Provided Assistance; Flight Crew Overcame Equipment Problem; General Maintenance Action
Aircraft
Cruising at FL400; we just checked in with Miami Center; passing URSUS intersection. Approximately ten minutes later the aircraft started pitching down abruptly. The speed started to increase rapidly so I disconnected the autothrottles and pulled back the thrust levers. I then disconnected the autopilot and initially followed the Flight Direct Guidance; the VVI and the altimeter. Both the FO and I noticed that the pitch and altimeter were not correct because we were still descending. I asked the FO to take the controls because it appeared that his instruments were correct. The FO started climbing back to FL400. About that time ATC inquired of our altitude and we told them we had a problem and to standby.The FO engaged CMD-B autopilot. At this point it looked like my altimeter was malfunctioning. We pressed the recall to find that we had a SPEED TRIM FAILURE - SINGLE CHANNEL. Approximately 12 minutes later; we get an UNABLE RNP message with the ANP bars closed and the ANP value increasing past 5.0. We ran the QRH for this and it required us to verify our position. We accomplished this by using the VORs. We informed center that we could no longer maintain our navigation using RNAV and would require vectors to proceed to [destination].About 50 miles from the airport; ATC said that the Command Center advised that they were [giving us special handling]. The FO and I discussed this earlier but felt that since this was not a control problem; special handling was not required. About 12 miles from the airport we got a Master Caution; and IRS light; the L IRS FAULT light was illuminated; all of the Captain's data was gone both on the PFD and ND; and the autopilot disengaged. The FO still had all his data and continued to fly the aircraft. The landing was uneventful. I informed Dispatch upon reaching the gate. I made a logbook entry for the IRS; the Speed Trim Fail light; and the Captain's altimeter.
[Report narrative contained no additional information.]
B737-700 flight crew reported loss of several navigation-related systems as well as the Captain's altimeter.