27th of January 2002
A Fokker 70 (PH-KZB) with 63 occupants (59 passengers, 2 cabin crew and 2 flight crew) had just taken off from Amsterdam Airport Schiphol, for its scheduled passenger service when the crew received a "LO QTY" light on the hydraulic panel and an "HYD SYS 1 LO QTY" warning on the MFDU (Multi-Function Display Unit)together with an aural warning and the Master Caution light. Alerting the crew that the fluid quantity in the reservoir for the #1 hydraulic system was low. The caution appeared just after gear retraction.
Fokker 70 Prototype, not the incident aircraft (Source; http://www.fokker-aircraft.info)
The relevant emergency checklist was completed and a return to Schiphol was initiated. Part of the checklist required the crew to switch of the hydraulic #1 system pumps. In accordance with the emergency checklist, the alternate gear down procedure was initiated on the approach. Both main gears locked in the down position, the nosegear however remained up in the nose landing gear bay. The approach was aborted and the crew contacted one of the fleet technical pilots for advice in an attempt to avoid a landing without the nose landing gear. With the reservoir quantity still indicating a quantity of 30%, it was suggested to turn on the pumps and attempt a normal gear down selection. The attempt was successful, the nose landing gear extended and the three greens on the instrument panel indicated to the crew that all gears
had locked down satisfactorily.
Fokker 70/100 hydraulic system (source smartcockpit.com)
After a successful landing passengers were disembarked and the aircraft was towed to the hangar for investigation and repair. The two main issues that needed to be resolved were;
The loss of fluid from hydraulic system #1
Failure of the nose landing gear to extend using the alter gear down procedure.
The failed hydraulic line (source; investigation report)
The cause of the first issue, loss of fluid from hydraulic system #1, was traced to a leaking return line from the left Aileron Actuator. The aluminium hydraulic line was replaced, the hydraulic system refilled.
The aircraft was jacked up for a landing gear retraction test using the normal gear system, pressurised by the #1 hydraulic system. The test was successful and all attention turned to the failure of the alternate extension of the nose landing gear. Several components from the nose landing gear extension and retraction system were sent to Fokker Services for testing, no explanation could be found for the failure of the nose landing gear extension. The next step was to check the door lock mechanism of the nose landing gear bay doors. The Flight Data Recorder analysis revealed that the doors were not opened during the alternate down selection, stopping the nose landing gear from extending. During the alternate down selection, the doors are opened mechanically via the alternate
gear extension handle in the cockpit. It was found that the mechanical adjustment was ever so slightly out of adjustment, this in combination with poor lubrication and bearings not operating smoothly had caused the nose landing gear to be "stuck" in the up position.
When these issues were corrected the alternate gear extension system was tested satisfactorily and the aircraft was released to service. The Type Certificate holder initiated an improvement program that involved;
New lubrication tasks
New bearings are being tested
The report into this incident by the Dutch Transport Safety Board (only in Dutch)is available by clicking on the .pdf file below;