This is the fifth segment in a series on wake turbulence, originally inspired by a reader's question. I've been meaning to get back to this series for quite some time now, as there's one more part to the story.
Earlier on, in Part 2, I discussed the obligations that air traffic controllers have concerning wake turbulence. If you like, you may revisit it here:
But controllers are only half the story; pilots also have their own role. Outside of the controller regulatory stuff, most of my reference material for this series has been pilot training information.
When I was going through my flight training, we discussed wake turbulence avoidance, particularly when training flights began to take us into airports where larger aircraft operated. Since the wake of the aircraft ahead of you is normally invisible, the pilot has to be aware of where the previous airplane is (and was), and fly his plane outside of where the wake vortices are anticipated to be. That sounds easy enough, since the vortices normally spread out from the wingtips and descend below the generating aircraft. But how does the following pilot ensure that his flight path is not below that of the aircraft ahead?
The standard recommendation is for the following pilot to set up his approach to the runway slightly above the normal glidepath, and then land further down the runway than the larger aircraft ahead. As I mentioned in the opening segment in the series, the vortices are caused by a wing that is creating lift. Once the wing stops lifting, the vortices are no longer being generated. So the following pilot aims to touch down beyond the point on the runway where the preceding aircraft landed.
This group of photos shows two successive aircraft arriving on Runway 24 Right. First, we see the heavy B767; note the touchdown point in relation to the glideslope shack and antenna between the runways:
When I was going through my flight training, we discussed wake turbulence avoidance, particularly when training flights began to take us into airports where larger aircraft operated. Since the wake of the aircraft ahead of you is normally invisible, the pilot has to be aware of where the previous airplane is (and was), and fly his plane outside of where the wake vortices are anticipated to be. That sounds easy enough, since the vortices normally spread out from the wingtips and descend below the generating aircraft. But how does the following pilot ensure that his flight path is not below that of the aircraft ahead?
The standard recommendation is for the following pilot to set up his approach to the runway slightly above the normal glidepath, and then land further down the runway than the larger aircraft ahead. As I mentioned in the opening segment in the series, the vortices are caused by a wing that is creating lift. Once the wing stops lifting, the vortices are no longer being generated. So the following pilot aims to touch down beyond the point on the runway where the preceding aircraft landed.
This group of photos shows two successive aircraft arriving on Runway 24 Right. First, we see the heavy B767; note the touchdown point in relation to the glideslope shack and antenna between the runways:
Now, observe the glide path of the succeeding Beech 1900, a considerably smaller aircraft; the pilot deliberately lands well past the point where the heavy jet touched down:
Of course, it isn't always that easy. The runway doesn't go on forever, so the pilot can't let too much of it go past; he's still got to have room to get his own craft on the ground and stopped. That's why we have increased spacing for a smaller aircraft following a large one; it allows time for the heavy jet's wake vortices to spread out away from the runway and begin to dissipate. Generally, the further behind the preceding aircraft you can be, the better your chances of avoiding a wake encounter.
Besides staying above it, another thing a pilot can do to avoid the wake from a preceding aircraft is to fly upwind of the other aircraft's flight path. To do this, the pilot will need to be aware of the wind direction at his altitude, which he certainly should already know. This is just like sitting upwind of a campfire; you let the wind blow the smoke (or wake vortices) away from you. If the wind shifts, you'll have to move your seat to a different spot (or adjust your flight path to the other side of the course or airway). Just like putting extra distance between you and the aircraft ahead, this technique can be applied enroute as well as in the approach-to-landing phase of flight.
Despite a pilot's best efforts to stay away from the wake of another aircraft, it can still happen. In busy terminal areas or at airway intersections, especially. For this reason, most airline pilots (and many charter pilots) receive what is known as upset training. While this used to have to be done using aerobatic aircraft, today's full-motion simulators are capable of offering the training without ever leaving the ground. The training consists of learning how to recognize and recover from sudden, uncommanded unusual attitudes, such as may result from an aircraft getting caught in the wake of another, particularly larger, aircraft. In preparation for this segment, I conducted an informal poll of air carrier pilots on the ground at LAX one Saturday afternoon. Pilots for every US carrier I asked told me that upset recovery is part of their regular recurrency training and sim rides.
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