Flight Crew Air Transport Pilot (ATP)
Distraction; Training / Qualification; Troubleshooting; Workload
Aircraft Equipment Problem Critical
Flight Crew Returned To Departure Airport; Flight Crew Landed As Precaution
Aircraft
During the Maintenance Check Flight [we] noticed a fuel imbalance on the left tank of 200 pounds less than the one indicated on the right tank on the initial climb out.  The flight crew decided to turn back and land at the airport. The unbalance increased to 400 pounds during cruise flight. We; the flight crew; decided to transfer fuel from the right to the left tank for balance purposes.  The transfer process was stopped during the descent and [we] continued to monitor the fuel gauges. The fuel unbalance was stabilized at the same 400 pounds during the initial descent all the way down until the landing.  We; the crew; nor the Mechanic on board who was assigned to monitor the left tank during the flight noticed any leak. While on the approach Tower was advised by another aircraft on the ground that while our aircraft was on short final [they] noticed something hanging or coming out from our left wing. The maintenance flight was completed unsatisfactory and the aircraft was written up for fuel unbalanced during flight.
A DHC-8-200 on a test flight developed a fuel imbalance which the Mechanic on board could not balance and so on return to the airport a ground observer commented that something was hang from or coming from the left wing.