Page 33 - Volume 16 Number 10

lue Line,White Arc,ed Radialin maximum available performance with one engine inoperative. We usually think of the speed identified on multiengine airplane airspeed indicators with a prominent blue line as the speed for best climb with an engine out.On takeoff we are (rightly) concerned about attaining blue line speed or better as quickly as possible, so that we have excess energy (speed) in the event of an engine failure close to the ground. But what role does blue line speed play on landing? Absolutely, one element of a well- flown approach in a multiengine airplane is to stay at or above blue line speed until you have committed to land. This is so the airplane is at or above VYSE in the early stages of a missed approach or go-around, in the gosh- you’re-having-a-bad-day event you lose an engine just as you are turning an arrival into a maximum-performance departure a short distance above the runway.We’ll come back to that phrase “committed to land” in a bit.Eventually in your approach, you reach the point where you reduce power and enter your landing flare. It’s time to trade the safety of blue line airspeed, which you no longer need, for the must-have proper airspeed for landing. The pilot who feels he or she should hold blue line airspeed all the way to touchdown is going to use a lot more runway than the airplane should need. Our emphasis on blue line airspeed may inadvertently lull us into unsafe landing behavior that,every now and then, puts a perfectly good airplane in the salvage yards.White ArcThe white arc of your airspeed indicator depicts the range of full-flap operating speeds. The “bottom” or slow end of the white arc is VSO—stalling speed in the full-flap, landing configuration. Single-engine or light twin, the goal is to gently stall the airplane just as the wheels touch the ground. To do so, the generally recommended final approach “over the fence” speed is 1.3 x VSO, enough for stall protection but not so fast you can’t decelerate without using excessive distance in the flare. Assuming engine-out concerns are secondary to the task of flare and landing, you’ll eventually slow to something approximating VSO as you touch down. Thus, 1.3 times the bottom of the white arc remains a valid speed target, even in twin-engine aircraft.Red RadialThe red radial speed, of course, is VMC: the minimum airspeed for control in the event of failure of the critical engine. The minimum speed for control if the non-critical engine fails is just a little slower, and not marked on the airspeed indicator. Airplanes with counter-rotating propellers have the same minimum controllable airspeed for either engine.VMC assumes the airplane is at maximum gross weight at the rearmost allowable c.g. location, withOCTOBER 2012TWIN & TURBINE • 31