A B737-700's pilot-static system malfunctioned causing airspeed and altimeter errors. The flight remained clear of RVSM airspace and the system returned to normal functioning after about forty-five minutes at cruise.
Synopsis
A B737-700's pilot-static system malfunctioned causing airspeed and altimeter errors. The flight remained clear of RVSM airspace and the system returned to normal functioning after about forty-five minutes at cruise.
Narrative
On the previous flight we had had an erroneous airspeed indication. We determined that the #2 airspeed indicator was in error by referring to the standby airspeed indicator and the Captain's airspeed indicator. After talking with Dispatch and Maintenance and considering the forecast for our destination; we decided to divert. We had to burn 45 minutes of fuel prior to landing at our divert airport. During those 45 minutes; the problem corrected itself. Maintenance checked the pitot static system and changed the #2 ADIRU. On this flight we started having the same problem as we climbed through 12;000.' It started with #2 airspeed indicator giving incorrect indications followed by incorrect altitude on #2 altimeter. Again we verified that the problem was with the First Officer's side. We calculated fuel burn to our destination below RSVM. After talking with Maintenance and Dispatch and considering the forecast for our departure airport and destination; we decided to continue to our destination at FL270. Again the problem corrected itself after about 45 minutes.
NASA callback
The reporter stated the malfunction on the first flight started at about 12;000 FT with the altimeter fluctuating plus and minus 100 FT. At about FL200 climbing; the First Officer's airspeed began fluctuating. Because of poor weather at the destination the crew diverted. The malfunction cleared itself before landing at the diversion airport. During the departure from the diversion airport with a new ADIRU that same sequence of altimeter and airspeed events occurred again. The crew elected to continue the flight below RVSM airspace because the destination weather had improved. The following day the reporter's maintenance department reported that the First Officer's altimeter and airspeed malfunctions were the result of a pitot tube malfunction.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.