Narrative:

Upon takeoff at ZZZ, the flap select knob was in the up position. When the airplane was taking off, I noticed the rate of climb was greatly reduced 300-500 FPM. After troubleshooting the problem (checking flaps up, gear up, mixture rich, wing locker doors closed), I decided to come back and land. When I landed I found the flaps were down with the flap select knob in the 'up' position. Then I noticed that the flap position pointer was at 45 degrees. Because it was night, I was unable to see the position pointer due to poor lighting. I cycled the flaps and they worked fine. The reduced performance of the airplane was the reason for returning to ZZZ airport. One last note: the flaps are not visible due to being split flaps. Therefore, when looking outside there would be no way to determine the flaps to be up or down. Callback conversation with reporter revealed the following information: the reporter stated the airplane was a C402 and is operated in a part 135 operation. The reporter stated the trip departed and the flap operation was normal and a log report was entered for maintenance. The reporter stated maintenance found a loose wire for the electrical driven flaps but is unaware of the fault location.

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Original NASA ASRS Text

Title: A C402 ON TKOF CLB AT 4200 FT DIVERTED DUE TO REDUCED CLB PERFORMANCE. FOUND FLAPS FULLY EXTENDED WITH SELECTED KNOB IN 'UP' POS.

Narrative: UPON TKOF AT ZZZ, THE FLAP SELECT KNOB WAS IN THE UP POS. WHEN THE AIRPLANE WAS TAKING OFF, I NOTICED THE RATE OF CLB WAS GREATLY REDUCED 300-500 FPM. AFTER TROUBLESHOOTING THE PROB (CHKING FLAPS UP, GEAR UP, MIXTURE RICH, WING LOCKER DOORS CLOSED), I DECIDED TO COME BACK AND LAND. WHEN I LANDED I FOUND THE FLAPS WERE DOWN WITH THE FLAP SELECT KNOB IN THE 'UP' POS. THEN I NOTICED THAT THE FLAP POS POINTER WAS AT 45 DEGS. BECAUSE IT WAS NIGHT, I WAS UNABLE TO SEE THE POS POINTER DUE TO POOR LIGHTING. I CYCLED THE FLAPS AND THEY WORKED FINE. THE REDUCED PERFORMANCE OF THE AIRPLANE WAS THE REASON FOR RETURNING TO ZZZ ARPT. ONE LAST NOTE: THE FLAPS ARE NOT VISIBLE DUE TO BEING SPLIT FLAPS. THEREFORE, WHEN LOOKING OUTSIDE THERE WOULD BE NO WAY TO DETERMINE THE FLAPS TO BE UP OR DOWN. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE AIRPLANE WAS A C402 AND IS OPERATED IN A PART 135 OP. THE RPTR STATED THE TRIP DEPARTED AND THE FLAP OP WAS NORMAL AND A LOG RPT WAS ENTERED FOR MAINT. THE RPTR STATED MAINT FOUND A LOOSE WIRE FOR THE ELECTRICAL DRIVEN FLAPS BUT IS UNAWARE OF THE FAULT LOCATION.

Data retrieved from NASA's ASRS site as of July 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.