Narrative:

After takeoff from runway 10; the landing gear lever was selected to the up position. The master caution lights illuminated and two EICAS messages were indicated: 'gear disagree' and 'gear door'. An expanded; non-normal gear position was displayed. It indicated that the left main body gear was locked down and all other gear was retracted. The B747 flight manual irregular procedures for these two EICAS messages were reviewed; however neither procedure provided guidance on how to retract a landing gear that is locked down and will not retract.dispatch and maintenance control were called. Maintenance control requested that we lower the landing gear and then retract it. Normal gear down indications were indicated; but once again; when the gear was selected up; the left body gear remained locked down. ATC informed us that another pilot had observed that something had fallen from our aircraft upon departure; but it was not known what the object was. ATC declared an emergency for our aircraft.the decision was made to return to the departure airport. The flight operations manual 'overweight landing versus fuel dumping' section was reviewed. We informed ATC that we would need to dump fuel. Fuel was dumped over the lake at 6;000 feet MSL. Total fuel at departure was 298;000 pounds. Fuel at landing was 134;500 pounds. Total fuel burned and dumped from takeoff to landing was 163;500 pounds. Fuel dumping was terminated as we crossed the western shoreline of the lake. We had planned to be at maximum structural landing weight upon touchdown. We landed at a weight of 632;500 pounds or 2;500 pounds overweight. It was deemed safer to land overweight rather than go-around or dump more fuel at low altitude. The landing was normal.city fire department emergency equipment was standing by for our arrival. Upon exiting the runway; fire department personnel inspected the airplane and informed us that everything appeared normal. At the gate; a maintenance supervisor informed us that a landing gear safety pin; without a flag attached; had been left in the landing gear. The pin had prevented gear retraction.

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Original NASA ASRS Text

Title: A B747-400 had to dump fuel and return to the departure airport when the left main body gear failed to retract due to an undetected locking pin.

Narrative: After takeoff from Runway 10; the landing gear lever was selected to the up position. The master caution lights illuminated and two EICAS messages were indicated: 'Gear Disagree' and 'Gear Door'. An expanded; non-normal gear position was displayed. It indicated that the left main body gear was locked down and all other gear was retracted. The B747 Flight Manual Irregular procedures for these two EICAS messages were reviewed; however neither procedure provided guidance on how to retract a landing gear that is locked down and will not retract.Dispatch and Maintenance Control were called. Maintenance Control requested that we lower the landing gear and then retract it. Normal gear down indications were indicated; but once again; when the gear was selected up; the left body gear remained locked down. ATC informed us that another pilot had observed that something had fallen from our aircraft upon departure; but it was not known what the object was. ATC declared an emergency for our aircraft.The decision was made to return to the departure airport. The Flight Operations Manual 'Overweight Landing versus Fuel Dumping' section was reviewed. We informed ATC that we would need to dump fuel. Fuel was dumped over the lake at 6;000 feet MSL. Total fuel at departure was 298;000 pounds. Fuel at landing was 134;500 pounds. Total fuel burned and dumped from takeoff to landing was 163;500 pounds. Fuel dumping was terminated as we crossed the western shoreline of the lake. We had planned to be at Maximum Structural Landing Weight upon touchdown. We landed at a weight of 632;500 pounds or 2;500 pounds overweight. It was deemed safer to land overweight rather than go-around or dump more fuel at low altitude. The landing was normal.City Fire Department emergency equipment was standing by for our arrival. Upon exiting the runway; Fire Department personnel inspected the airplane and informed us that everything appeared normal. At the gate; a Maintenance Supervisor informed us that a landing gear safety pin; without a flag attached; had been left in the landing gear. The pin had prevented gear retraction.

Data retrieved from NASA's ASRS site as of April 2012 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.