Event Description
The first officer landed the airplane on runway 35L in a slight left crosswind. The flight crew had previously confirmed that the landing gear was down and locked. Upon touchdown, the landing gear warning horn sounded, and the right main and nose landing gears retracted. The airplane slid to a halt on the right side of the runway.
Flight Data Recorder Information
Data from the flight data recorder indicated that the landing gear was extended and showed a down-and-locked indication based on nose landing gear position. The nose landing gear became unlocked (unsafe) 2 seconds after the radio altitude reached 0 feet. Hydraulic pressure dropped to approximately 2,700 psi momentarily before returning to normal (about 3,000 psi).
Component Testing
The following components were subjected to various tests, and no anomalies were noted:
- Proximity switch electronics unit (PSEU)
- Right main landing gear harness and proximity switches
- Landing gear selector valve
- Hydraulic pressure sensing valve
- Landing gear control assembly
Hydraulic fluid samples drawn from the filter pack, right main landing gear down lock assist actuator, and the return line for the landing gear selector valve were analyzed. No significant anomalies were noted. Partial systemic wiring tests were unremarkable.