What happened
On January 27, 2002, a Fokker F.28 Mk. 0070, registration PH-KZB, performing a passenger flight, was forced to return to Amsterdam Airport Schiphol shortly after takeoff. The crew received a warning indicating low quantity in hydraulic system 1. Following emergency checklists, the crew attempted the alternate gear down procedure; however, the nose gear failed to extend. After consulting with ground technical support, the crew reactivated the hydraulic pumps. Because the system still contained approximately 30% fluid, a standard gear down procedure was attempted, which successfully deployed the nose gear. The aircraft landed at Schiple without further incident, resulting in no injuries to the 59 passengers, though the aircraft sustained light damage.
The investigation
Post-landing inspections revealed that the hydraulic return line for the left aileron actuator had nearly fractured, causing fluid to leak during the initial gear retraction. While the breakage of aluminum lines was a known issue previously noted by Fokker Services, the investigation focused on why the alternate gear down system failed to function. Following repairs to the hydraulic line, the aircraft was jacked to test the landing gear, but the failure of the alternate system could not be reproduced. Subsequent testing of nose gear hydraulic components by Fokker Services found no faults in individual or combined parts. Analysis of the Flight Data Recorder (FDR) eventually revealed that the nose gear door uplock lever failed to move during the alternate gear selection, which interrupted the gear release process.
Findings
The investigation determined that the failure of the nose gear to deploy via the alternate mechanism was caused by a combination of inadequate lubrication, improper adjustments, and heavy-running bearings within the nose gear door lock mechanism. While the hydraulic leak was the initial trigger for the return, the mechanical failure of the door locks prevented the secondary deployment method from working.