General Principles - Landing — Page 273, Lesson 340

Let’s start with the landing distance itself, because that’s the foundation of everything we’re about to do. The landing stage of flight is defined as that stage which commences from 50 ft above the landing threshold and terminates when the aeroplane comes to a complete stop. That 50 ft point is sometimes referred to as the landing screen height. And here’s a key contrast for you: the landing screen height is fixed at 50 ft for all classes of aeroplane, unlike the take-off screen height, which is 35 ft for Class A aeroplanes and 50 ft for Class B aeroplanes. So on landing, everyone uses 50 ft; on take-off, it depends on the class. Now, from the approach down to that landing screen height, the aeroplane must have attained the landing reference speed, known as VREF. Let me define that precisely. For Class A aeroplanes, VREF must be no less than the greater of two values: 1.23 times the stall reference speed in the landing configuration, which we write as 1.23 VSR0, and the velocity of minimum control in the landing configuration, which is VMCL. So for Class A, you take whichever of those two is larger, and VREF can’t be below it. For all other classes of aeroplane, VREF must be no less than 1.3 times the stall speed in the landing configuration, written 1.3 VS0. Why is VREF so important? Because the landing distances in the aeroplane flight manual are based on aeroplanes flying at VREF. So if a landing aeroplane is not at VREF, the landing distance given by the manual will not be achieved by the pilot. A landing carried out at a speed other than VREF could seriously jeopardize the safety of the landing. That’s a direct cause-and-effect: the manual’s numbers assume VREF, so if you deviate from it, the published distance no longer applies. Now let’s break the landing itself into two parts. We call these the airborne section and the ground run, or landing roll. The first part, the airborne section, starts from the landing screen height of 50 ft and ends when the aeroplane’s main wheels touch the landing surface. The airborne section is usually given as being about 1000 ft in length. Within the airborne section, certain criteria apply — and that’s where we’ll pick up next.