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Why Are Porpoise Landings So Dangerous?

They say any landing you walk away from is a good one, but that's not always the case. Sometimes landings are bad, and other times they're downright dangerous. Porpoising on landing is a perfect example. If you don't correct properly, you'll leave your nose gear and propeller shattered in pieces on the runway.

What Is A Porpoise Landing?

A porpoise landing is a bounced landing that, if not recovered, results in your plane touching down nose first. If you let it continue, it will set your plane off into a series of "jumps" and "dives", like a real porpoise. Porpoise landings can happen when you are flying too fast during touchdown, or if your descent rate is too high at touchdown. And if you force your airplane down and touch the nosewheel first, you can send your plane into an unrecoverable sequence of events. Check out this YouTube clip of a porpoise landing that doesn't end well:

Why Did The Airplane Porpoise?

Let's break down what happened in this particular landing.

00:02

The airplane approaches low and fast, and floats over the runway threshold.

00:03

The pilot bounces the landing and then forces the airplane back on to the runway, landing nose-first.

00:04

The main gear strike the runway and intertia forces the tail down, rapidly increasing the angle-of-attack on the wings. Because the plane is moving quickly, the wings generate enough lift to bring the main gear off the runway again. The nose gear remains on the runway because the pilot is holding the control yoke in a neutral or slightly-forward position. As the plane continues down the runway, the pilot will introduce pilot induced oscillations as they try to counter the porpoise, using forward and back pressure on the yolk. This only makes things worse.

00:05

The second and third major porpoise oscillations occur in a 1-second time span. The oscillations become progressively worse each time the landing gear strike the runway.

00:07

All three landing gear leave the runway for the first time since the initial landing bounce. At this point the oscillations are happening so rapidly and becoming so intense, it's unlikely the landing can be recovered.

00:08

The aircraft lands nose-low again, this time with the right main gear lifting up over a foot off the ground.

00:09

With the highest porpoise yet, it's only a matter of time until the nose gear fails.

00:10

The nose gear makes contact with the runway and snaps off. The propeller strikes the ground and debris scatters behind the airplane.

00:11

The pilot wishes they had executed a go-around.

Porpoise Landing Diagram

What To Do If It Happens To You

So what should you do if you start to porpoise a landing? Immediately executing a go-around is the safest thing to do. Because porpoise oscillations occur so rapidly, flight control inputs to correct the oscillations are difficult, if not impossible to accomplish. In the video, the accident happened less than 8 seconds after the first touchdown.

By going-around, you'll quickly leave the ground and get a second chance at the landing. After all, a go-around is always better than an accident report phone call to the NTSB.


Colin Cutler

Colin is a Boldmethod co-founder, pilot and graphic artist. He's been a flight instructor at the University of North Dakota, an airline pilot on the CRJ-200, and has directed development of numerous commercial and military training systems. You can reach him at colin@boldmethod.com.

Images Courtesy:

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