Narrative:

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 first officer and I noticed that the pitch and altimeter were not correct because we were still descending. I asked the first officer to take the controls because it appeared that his instruments were correct. The first officer 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 first officer 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 first officer 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 left IRS fault light was illuminated; all of the captain's data was gone both on the pfd and nd; and the autopilot disengaged. The first officer 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.

Google
 

Original NASA ASRS Text

Title: B737-700 flight crew reported loss of several navigation-related systems as well as the Captain's altimeter.

Narrative: 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.

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.