How and why landing gear could collapse on landing a Boeing 737

AIRPORT--Without speculating about today’s event, the following mechanisms are recognized by the U.S. National Transportation Safety Board (NTSB) and by the Transportation Safety Board of Canada (TSB), as well as in aviation safety literature and investigations as potential contributors to landing gear collapse on landing in 737 series aircraft. Only the operator, manufacturer, and accredited investigators can determine the cause in any specific case.

𝐎𝐯𝐞𝐫𝐥𝐨𝐚𝐝 𝐟𝐫𝐨𝐦 𝐥𝐚𝐧𝐝𝐢𝐧𝐠 𝐝𝐲𝐧𝐚𝐦𝐢𝐜𝐬: An unstabilized approach or a hard, nose-first touchdown can exceed structural limits at the nose gear, leading to failure during or after touchdown. Excessive sink rate or improper pitch attitude can concentrate loads beyond design margins.

𝐅𝐚𝐭𝐢𝐠𝐮𝐞 𝐜𝐫𝐚𝐜𝐤𝐢𝐧𝐠 𝐢𝐧 𝐭𝐫𝐮𝐧𝐧𝐢𝐨𝐧 𝐩𝐢𝐧𝐬 𝐨𝐫 𝐫𝐞𝐥𝐚𝐭𝐞𝐝 𝐡𝐚𝐫𝐝𝐰𝐚𝐫𝐞: Main landing gear trunnion pins and attachment fittings can develop fatigue cracks over time, especially if prior maintenance introduced finish damage, corrosion, or grinding beyond limits. Progressive cracking can culminate in fracture under landing loads.

𝐆𝐞𝐚𝐫 𝐬𝐡𝐢𝐦𝐦𝐲 𝐚𝐧𝐝 𝐭𝐨𝐫𝐬𝐢𝐨𝐧 𝐥𝐢𝐧𝐤 𝐝𝐚𝐦𝐚𝐠𝐞: Excessive wheel or gear shimmy can overstress torsion links, bushings, and fasteners. Fracture or loss of torsion link integrity can allow destructive oscillations that contribute to collapse or severe gear damage during rollout.

𝐋𝐨𝐜𝐤𝐢𝐧𝐠 𝐚𝐧𝐝 𝐛𝐫𝐚𝐜𝐢𝐧𝐠 𝐢𝐬𝐬𝐮𝐞𝐬 𝐨𝐫 𝐦𝐢𝐬-𝐫𝐢𝐠𝐠𝐢𝐧𝐠: Side braces, drag braces, and down-lock mechanisms must engage and be correctly rigged. If weakened by wear, damage, or mis-rigging, or if subjected to abnormal side loads, the gear can unlock or move out of its intended geometry under load.

𝐂𝐨𝐦𝐩𝐨𝐧𝐞𝐧𝐭 𝐨𝐫 𝐚𝐱𝐥𝐞 𝐟𝐚𝐢𝐥𝐮𝐫𝐞𝐬 𝐚𝐭 𝐭𝐡𝐞 𝐧𝐨𝐬𝐞 𝐠𝐞𝐚𝐫: Structural failures of inner cylinders, axles, or associated components can occur due to hidden defects, corrosion, or prior overloads, leading to loss of support during taxi, touchdown, or rollout.

Actual determinations rely on a structured process, which includes aircraft inspection, teardown of damaged components, review of maintenance and overhaul records, analysis of flight data and cockpit voice recorders where applicable, and coordination with the aircraft manufacturer and the relevant civil aviation authorities.

𝐓𝐨𝐨 𝐇𝐚𝐫𝐝

A pilot can land an aircraft “too hard” and trigger a landing gear collapse. A “hard landing” occurs when the vertical speed at touchdown exceeds the aircraft’s design limits, sending forces through the landing gear and fuselage that can cause structural failure. While gear is designed with safety margins, an excessively hard touchdown can overwhelm those margins, especially if combined with poor pitch angle or crosswind.

So, while rare, a landing that is too hard has directly caused a 737’s landing gear to collapse. This is why airlines track hard-landing data from the flight data recorder, and maintenance crews must perform structural checks if a hard-landing threshold is exceeded.

𝐏𝐢𝐥𝐨𝐭 𝐄𝐟𝐟𝐨𝐫𝐭

When an aircraft’s landing gear collapses, the pilot is immediately faced with one of the most demanding scenarios in aviation. The landing gear is not only the structural support for the aircraft on the ground, it also stabilizes the aircraft’s balance during rollout. Once that support is compromised, the aircraft can yaw violently to one side, drag a wingtip, or scrape the engine nacelles and fuselage against the runway surface.

For the pilots, this means they must apply maximum control inputs—using rudder, ailerons, and sometimes asymmetric thrust—to keep the aircraft tracking straight on the runway and prevent a total loss of directional control. They must also coordinate with braking systems that may now be compromised, since part of the landing gear is not functioning.

Communication and split-second decision-making become critical: one pilot focuses on controlling the aircraft while the other manages checklists, communicates with the tower, and prepares for an evacuation if needed.

The challenge is heightened because everything happens in seconds, at relatively high speeds (often 120–150 knots on touchdown). It requires intense training, coordination, and composure under pressure. The fact that in many such incidents passengers walk away unharmed speaks volumes about both pilot training and the design redundancies of modern aircraft.

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