DEN04IA026

On November 29, 2003, at 0840 mountain standard time, a Boeing 737-3M8, N303FL, operating as Frontier Airlines flight 567, experienced a momentary lock up of the captain and first officer's aileron and flight spoiler controls, while on final approach into Denver International Airport (DEN), Denver, Colorado. The airline transport certificated captain and first officer, 3 cabin crewmembers, and 130 passengers were not injured. Visual meteorological conditions prevailed. The scheduled domestic passenger flight was being conducted under the provisions of Title 14 CFR Part 121. An instrument flight rules (IFR) flight plan had been filed for the flight that departed Milwaukee, Wisconsin, at 0637 central standard time.

The captain reported that they were on final approach approximately 1/4 mile from the end of the runway when he applied right aileron to correct for a crosswind. "The [control] yoke felt like it had 'bound up'." He had to use excessive pressure to get the control yoke to respond. An uneventful landing was made at DEN. After landing, he cycled the yoke left and right. After a few cycles, it seemed to free up. The captain said that while taxiing to parking with the number 2 engine shut down, he made a sharp left turn and the tiller [wheel] seemed to "bind up."

After the passengers had deplaned, the airplane was taken to Frontier's maintenance hangar where mechanics performed a "[nose landing gear] wheel steering test [in accordance with Maintenance Manual] 32-51-00. Checked good. Performed cable tension to nose wheel steering [in accordance with Maintenance Manual] 32-51-00. Tension good. Found [right hand] nose steering accumulator leaking. Leak limits good [in accordance with Maintenance Manual] 29-00-00, page 605. Inspected case drain filters. Found no discrepancies [reference Maintenance Manual 24-15-91]. Removed and reinstalled #2 engine case drain plug to inspect. Found no discrepancies [reference Maintenance Manual 29-15-00]. Inspected [left hand] and [right hand] aileron cables from main [wheel well] outboard visually. No discrepancies noted. Complied with flight control movement card 7-9002. No discrepancies noted. Performed aileron PCU internal leak check procedure [reference Maintenance Manual 84-00-00. No discrepancies noted. Aircraft is released for operational check flight. Performed post operational check flight, walk around inspection." During the test flight, no discrepancies were noted and the airplane was returned to service.

The digital flight data recorder (DFDR) was removed from the airplane and sent to NTSB's Vehicle Recorder Laboratory for readout. According to the DFDR engineer, no data was recovered that would explain the event as described by the captain.