Landing Gear — Page 115, Lesson 153

Let’s start with the core idea of this section, because it sets up everything else about the landing gear. When the landing gear is fully retracted or fully extended, it is locked into position. That locked state is what makes it resistant to damage from high airspeeds. Think of it this way: the gear is either tucked away in its bay, or it’s down and ready for landing, and in both cases it’s held firmly by a locking mechanism. But here’s the critical point: while the gear is actually moving—either extending or retracting—there is no locking mechanism engaged. The only thing resisting the airflow during that operating phase is the extension and retraction mechanisms themselves. So during transit, the gear is at its most vulnerable, and that’s why there are speed limits tied to operating the gear. Now, there’s a second aerodynamic concern. On some aircraft, the landing gear may swing or swivel in odd directions in order to tuck into their recesses. That odd motion can cause unusual aerodynamic behaviour in the rest of the aircraft if it happens at high speeds. So the design isn’t just about fitting the gear into a small space—it’s about how that movement disturbs the airflow around the whole airframe. That brings us to the speed limits. Once the landing gear is extended, it’s rare that a pilot would exceed VLO. Let me define that: VLO is the maximum speed at which the landing gear can be safely operated—that is, extended or retracted. Most of the time, the gear is lowered shortly before landing, and at that point the pilot is doing everything possible to slow the aircraft down, so VLO isn’t a concern. But there’s a different case. If an aircraft has to be flown a long distance with the gear extended—say, on a ferry flight to a repair facility—the pilot would fly at VLE. VLE is the maximum speed at which the aircraft can be flown with the landing gear extended. So VLO is about the act of moving the gear; VLE is about sustained flight with the gear down. Two different limits, two different situations. Now let’s move to the emergency lowering systems. This is the backup for when the main system fails. The purpose is simple: provide a means of extending the landing gear and locking it in the down position, in case the main system fails. Here’s how it works on some aircraft. The uplocks—those are the mechanisms that hold the gear in the retracted position—are released mechanically or electrically by manual selection. So the pilot makes a deliberate selection, and that releases the gear from its locked-up state. Once released, the landing gear “free falls” under its own weight. That’s gravity doing the work—no hydraulic or electrical power needed. And as it falls, the downlocks—the mechanisms that hold the gear in the extended position—are engaged mechanically. So the gear locks down purely by mechanical action. Now, here’s an important assumption and a consequence. If the gear has been lowered by the free-fall method, then it must be assumed that the main source of power to the gear has failed. Why does that matter? Because if there’s no power, there’s no way to retract the gear after it’s been released. And that means the doors will remain open. And that’s where the size of the doors becomes a problem on some aircraft. If the doors are large and they stay open, there’s a chance they will contact the ground upon touchdown—unless the landing is exceptionally good. So the free-fall system gets the gear down and locked, but it leaves the doors hanging open, and that creates a real risk on landing. Let me tie this together. You have two speed limits: VLO for operating the gear, VLE for flying with it extended. You have the locked versus operating states, and the vulnerability during transit. And you have the emergency system: uplocks released manually, gravity free-fall, mechanical downlocks, and the consequence that doors stay open because power is assumed failed. That’s the full picture of this section.