The Saab 340 landing gear is hydraulically actuated and electrically controlled via a selector valve that directs the hydraulic fluid flow. The main landing gear have two wheels that are mounted on conventional oleo struts. The gear is extended via the release of mechanical uplocks, mounted on the gear drag brace (nose and main), that permit the gear to free fall into position. The drag brace stabilizes the gear when down. Assist springs insure full down locking. Mechanical down locks engage when the gear is extended and are released hydraulically for gear retraction. All the gear swing forward during retraction.
Left main gear bay, with inner door dropped for preflight inspection.
Like the mains, the nose gear also has two wheels and assist springs to ensure full down locking.
Brake wear indicator pin. Preflight item: note required safety wire.
Right main inboard tire change.
There is a switch on each gear down lock and up lock that sends signals for gear position indications and warnings. The landing gear control panel illuminates three green lights when all gear are down locked and the lights extinguish when all are up locked. If any gear is not in the selected position, the gear disagreement light will illuminate. The warning system indicates that the gear is unsafe by:
- illumination of the amber disagreement light in the gear handle
- master warning CONFIG on the CWP panel
- the sounding of an intermittent warning horn
An unsafe gear alert will be triggered when:
- Any gear is not downlocked and
- Radio Altimeter altitude is <500ft and
- one or both power lever is below the 64° PLA
- Flaps are extended beyond 15 degrees with all gear not down and locked
The horn may be silenced and reset by pushing the illuminated red MASTER WARNING light. If the gear is not down and locked and the flaps are lowered to at least 20°, the horn will sound. It cannot be silenced until the flaps are retracted or the gear is locked down. In both cases, the MASTER WARNING lights illuminate and the configuration horn sounds.
EMERGENCY GEAR EXTENSION
A hand pump is used to extend the gear which eliminates the check
valve, isolating hand pump pressure from the main hydraulic system and
allowing hand pump pressure to charge the main accumulator. The handle of the pump is inserted into the circular recepticle for pump operations and is stowed behind the first officer on the cockpit wall.
The EMERG LDG gear panel is located in the floor boards under the first officers left foot. Pulling the EMERG LDG handle mechanically actuates the emergency uplock release valve which directs emergency accumulator pressure to all three uplock release actuators and creates a hydraulic return path from all three gear actuators. Once the uplocks are disengaged, the gear is allowed to free-fall to the down and locked position. Assist springs on each gear assist air forces and gravity to lock the gear down. In addition to actuating the emergency uplock release valve, pulling the EMERG LDG handle also electrically detonates explosive bolts in each main wheel well. This separates the door actuating linkage from the mains, allowing them to remain open after gear extension. The circuit is routed through the left main gear squat switch to prevent inadvertent detonation on the ground. Pumping the hand pump until the gear is down and locked takes about 30 pumps.