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Plane Answers: Sudden acceleration on landing and lining up on final approach
Darren from Engadget asks:
Just got back from a LIR -> ATL -> RDU trip, and I thought of a question. When the plane (we were on a 737) is just seconds from touching down on the runway, it feels & sounds like the plane suddenly accelerates. For a few minutes leading to landing, it feels like we're slowing down, and right before the rubber hits the road, there's like a small burst in speed, followed by touch down and then massive wind as I assume the engines are thrown in reverse to stop us.
So, what's that acceleration just before touch down for? Or am I dreaming? Thanks!
Nope, I'm sure you experienced this.
Occasionally if a pilot is a bit slow (say 2 or 3 knots below your 'target speed') they can add a small boost of power in the flare to cushion the inevitable thump of a landing. But it's really not a very good technique to use regularly.
And some pilots don't just use it when they're a tad slow, but they use it as a substitute for a finessed flare on every landing.
It can lead to a very 'flat' and fast landing. Touching down like this eats up a lot of runway unnecessarily and puts more wear on the brakes and tires.
You'll hear in this takeoff and landing video the instructor repeat "flare and squeeze" to the captain as he's about 30 feet over the runway. He's telling him to start his flare, or round out the glide path angle to allow for a smoother touchdown and to "squeeze" or pull the power back to idle before touching down.
And you're right, the noise you're hearing after landing comes from the reverse thrust mechanism which is simply a set of 'blocking doors' that divert the thrust out the sides of the cowl and forward, angled away from the engines.
How important is a reference point in lining up for landing?
If the weather is clear, we are often able to make up our own final approach to landing in, for example, the Caribbean. At densely populated areas and in the weather (flying on instruments) we fly an approach that usually has a straight-in segment of about 10 miles. We're almost never turned in any closer than 3 miles out.
As you can see from the video linked in Darren's question above, while on the final approach it's easy to tell if you're lined up correctly with the runway.
In San Juan, Puerto Rico, we line up for one runway (10) and in the last 300 feet make a turn to another runway (8) for landing. It's a 'charted' visual approach procedure that's rather fun.
The approach is similar to the ending of this video I took while flying in a small Diamond DA-20 airplane:
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