Narrative:

En route left engine oil pressure went to 0. All other indication normal. Dismissed incident as isolated failure of indicator. All circuit breaker's normal. On approach I called for flaps 10 degrees. Aircraft required substantial right aileron. Left flap indicated 0, right flap indicated 10 degrees. Returned flaps to 0, both flap indicators returned to 0, aileron control returned to neutral. All hydraulic pumps were on and hi. Left system pressure 1500, right system pressure 3000. Attempted to restore left system pressure (quantities were normal), recycled pump switches with no success. Fuel on board was 6700 pounds. Rejected request to go to mem. Diverted to atl. Used longest runway with equipment. Made 0 degree flap landing. Maintenance could find nothing wrong with aircraft. I flew the same aircraft the next day. At the 10 degree flap setting aircraft is out of rig and requires right aileron to maintain wings level. I suspect a loss of power to left 28 vacuum instrument bus caused the erroneous indications. This, coupled with the aircraft's response to flap extension, duped me into believing I had a split flap. Callback conversation with reporter revealed the following: company is going to check aircraft for flap extension rigging. Flap system does have a cable bus, but if not within tolerance could allow some uneven extension of flap. FAA has investigated incident and accused crew of not turning on left hydraulic pumps but since he has sent description with inoperative instrument, even FAA should realize reason hydraulic pressure did not indicate up was inoperative left AC bus and he has no further follow up from FAA.

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Original NASA ASRS Text

Title: ACR MLG SUSPECTING SPLIT FLAP DIVERTS TO ALTERNATE AND MAKES NO FLAP LNDG.

Narrative: ENRTE LEFT ENG OIL PRESSURE WENT TO 0. ALL OTHER INDICATION NORMAL. DISMISSED INCIDENT AS ISOLATED FAILURE OF INDICATOR. ALL CB'S NORMAL. ON APCH I CALLED FOR FLAPS 10 DEGS. ACFT REQUIRED SUBSTANTIAL RIGHT AILERON. LEFT FLAP INDICATED 0, RIGHT FLAP INDICATED 10 DEGS. RETURNED FLAPS TO 0, BOTH FLAP INDICATORS RETURNED TO 0, AILERON CTL RETURNED TO NEUTRAL. ALL HYD PUMPS WERE ON AND HI. LEFT SYS PRESSURE 1500, RIGHT SYS PRESSURE 3000. ATTEMPTED TO RESTORE LEFT SYS PRESSURE (QUANTITIES WERE NORMAL), RECYCLED PUMP SWITCHES WITH NO SUCCESS. FUEL ON BOARD WAS 6700 LBS. REJECTED REQUEST TO GO TO MEM. DIVERTED TO ATL. USED LONGEST RWY WITH EQUIP. MADE 0 DEG FLAP LNDG. MAINT COULD FIND NOTHING WRONG WITH ACFT. I FLEW THE SAME ACFT THE NEXT DAY. AT THE 10 DEG FLAP SETTING ACFT IS OUT OF RIG AND REQUIRES RIGHT AILERON TO MAINTAIN WINGS LEVEL. I SUSPECT A LOSS OF PWR TO LEFT 28 VACUUM INSTRUMENT BUS CAUSED THE ERRONEOUS INDICATIONS. THIS, COUPLED WITH THE ACFT'S RESPONSE TO FLAP EXTENSION, DUPED ME INTO BELIEVING I HAD A SPLIT FLAP. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: COMPANY IS GOING TO CHK ACFT FOR FLAP EXTENSION RIGGING. FLAP SYS DOES HAVE A CABLE BUS, BUT IF NOT WITHIN TOLERANCE COULD ALLOW SOME UNEVEN EXTENSION OF FLAP. FAA HAS INVESTIGATED INCIDENT AND ACCUSED CREW OF NOT TURNING ON LEFT HYD PUMPS BUT SINCE HE HAS SENT DESCRIPTION WITH INOP INSTRUMENT, EVEN FAA SHOULD REALIZE REASON HYD PRESSURE DID NOT INDICATE UP WAS INOP LEFT AC BUS AND HE HAS NO FURTHER FOLLOW UP FROM FAA.

Data retrieved from NASA's ASRS site as of August 2007 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.