Operation & Indication - Landing Gear - Airframes & Aircraft Systems #17

Summary

This lesson delves into aircraft landing gear systems, focusing on the hydraulic operation of gear extension and retraction. It explains how electrical indicating systems and mechanical indicators provide crew with gear position and lock status, using micro switches and proximity sensors. The hydraulic system, driven by engine pumps, includes sequence valves and actuators to ensure gear and door operation. The lesson also covers gear indicator lights, which signal gear status, and the importance of one-way restrictor valves in preventing cavitation and controlling gear speed.

Takeaways

• ✈️ Landing gear position and lock status are crucial for flight safety, and aircraft use both mechanical and electrical systems to indicate their status.
• 🔒 Mechanical indicators like pop-up buttons or periscopic viewers provide a physical confirmation that the landing gear is down and locked.
• 💡 Electrical indicating systems use micro switches or proximity sensors to monitor the position of the landing gear and provide a visual signal to the crew.
• 🟢 A green light on the landing gear position indicator signifies that the gear is down and locked, while a red light indicates the gear is not locked in the selected position.
• 🚫 Red lights also serve as a disagreement indicator, illuminating when there is a discrepancy between the selected gear position and the actual position.
• 🔧 Modern aircraft often use proximity switches, which are electronic devices without moving parts, for more reliable gear position detection.
• 💧 Hydraulic systems are commonly used for the operation of landing gear, with engine-driven pumps providing the necessary power, and backup systems for redundancy.
• 🔄 Sequence valves play a key role in controlling the order of operations for the landing gear and doors, ensuring safe and proper extension and retraction.
• 🛠️ The landing gear is locked down by a geometric lock mechanism, and an up lock roller engages with an actuator to secure the gear in the up position.
• 📉 One-way restrictor valves are used to control the speed of the landing gear's movement and prevent cavitation in the hydraulic system.
• 📲 Newer aircraft may feature LCD screens that provide additional information about the landing gear system, enhancing the crew's situational awareness.

Q & A

What is the purpose of the electrical indicating system in an aircraft's landing gear?

The electrical indicating system provides a positive indication to the crew of the operation of the locks and the position of the landing gear, ensuring they know if each landing gear is securely locked down.

How do micro switches contribute to the landing gear indication system?

Micro switches are mechanically operated electrical switches that make or break electrical circuits when the gear reaches the required position, causing the landing gear position indicator on the instrument panel to change.

What is the difference between micro switches and proximity switches in landing gear indication?

Micro switches are mechanically operated with moving parts, activated by a striker plate. Proximity switches, on the other hand, are electronic devices with no moving parts that activate when the sensor and target are in close proximity.

Why are sensors duplicated in the landing gear system?

Sensors are duplicated for safety reasons to ensure that if one sensor fails, the other can still provide an accurate indication of the landing gear's position and lock status.

What is the function of the mechanical indicators in the landing gear system?

Mechanical indicators, such as buttons that pop up on the wing or periscopic viewers in the cockpit, show that the landing gear is down and locked, providing a backup in case the electrical indicating system fails.

What colors of lights are typically used to indicate the status of the landing gear on an aircraft's instrument panel?

A green light indicates that each gear is locked down, a red light indicates the gear is not locked in the selected position, and no lights indicate the gear is up and locked.

How does a hydraulically operated landing gear system function?

A hydraulically operated landing gear system uses hydraulic power, typically supplied by engine-driven pumps, to extend and retract the landing gear. It involves components like actuators, locks, and sequence valves to control the operation.

What is the role of the one-way restrictor valve in the hydraulic landing gear system?

The one-way restrictor valve controls the speed of the landing gear lowering and prevents cavitation in the hydraulic system by regulating the flow of fluid through the up or return line.

Why is the restrictor valve placed in the upline instead of the downline during the gear lowering process?

Placing the restrictor valve in the upline prevents cavitation, which could occur if the restrictor was in the down pressure line due to the suction caused by the weight of the gear on the actuator piston.

How do modern aircraft with LCD screens display landing gear information?

Modern aircraft with LCD screens use electronic centralized aircraft monitor (ECAM) presentations to provide detailed information about the landing gear system, including the status of the gear and doors, depicted by symbols and colors.

What does the sequence of lights indicate during the landing gear extension and retraction process?

During the extension and retraction process, the lights indicate the status of the landing gear: red light for disagreement between the lever and the gear, green light for gear down and locked, and no lights for gear up and doors closed.