Take a look at FlightDeck Solutions’ B737NG Landing Gear Lever. The product is crafted with great precision, including this red Landing Gear Override Trigger: Of course, in the world of flight simulation, this Override Trigger is just a cosmetic piece and doesn’t actually work. So, what is its purpose in reality?

Below is an excerpt from the textbook “Turbine Engine Aircraft Structure and Systems”.

When the landing gear lever is in the “UP”, “DOWN”, or “OFF” position, there are detents to secure it, preventing the landing gear from being retracted due to accidental contact. In the air, the pilot must pull the lever out to move it.

The landing gear lever lock relay is controlled by the aircraft’s air/ground sensors. When the aircraft is parked on the ground, the air/ground sensor sends a signal, de-energizing the landing gear lever lock relay. The locking pin of the lever lock rises, restricting the landing gear lever to only be moved to the “DOWN” or “OFF” positions.

To prevent the inability to retract the landing gear in flight due to a malfunction in the lever lock, the lever is equipped with an override trigger. This device allows the lever to bypass the locking pin and be moved to the “UP” position when the pin is raised.

The mechanical ground lock for the landing gear is the final line of defense against retraction, as shown below. After the aircraft lands, a lock pin is inserted into the alignment hole of the landing gear downlock, and a red flag is attached to warn personnel. The flag features the “REMOVE BEFORE FLIGHT” text. Before takeoff, the ground lock pin must be removed and shown to the crew for verification. If the ground mechanical lock is not released, the aircraft will have to return to the airport after takeoff because the landing gear cannot retract.

By the way, if the Override Trigger is used to place the lever in the “UP” position, and then the pin on the ground mechanical lock is removed, what would happen to the aircraft? Take a look at this news report: Passengers Board as Flight Suddenly “Kneels” – Incident on Air China Flight CA941; 5 Crew and 3 Passengers Injured and Sent to Hospital:

The accident occurred at 5:10 AM. Passengers were boarding at the time. Most of the crew were already in their seats, and some passengers had entered the cabin. Just as some passengers were still boarding, the aircraft fuselage shook violently. Immediately after, the nose pitched forward and slammed heavily onto the ground. Amidst the screams of passengers, some boarding passengers fell down the stairs, and some passengers inside the cabin also fell over.

Airport staff who quickly arrived at the scene discovered that the aircraft’s nose landing gear had retracted. The nose had smashed into the ground, causing some deformation to the bottom. The aircraft began to leak fuel, and the engines under both wings had also scraped the ground.

Of course, under normal circumstances, if pre-flight preparations are performed according to the manual, such an incident would not occur. Regarding the China民航 Boeing 767 accident above, according to the explanation here, the cause was as follows:

It was related to poor communication between two maintenance crews. The previous crew was troubleshooting a landing gear fault, but the following crew was unaware of this and removed the safety pin, preparing to dispatch the aircraft shortly after. Consequently, the previous crew overrode the landing gear lever for testing, and the aircraft "knelt".

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