Definition
A pilot-induced oscillation during landing or takeoff in which the airplane bounces between its nosewheel and main wheels in a progressively worsening rocking motion. It typically begins when the airplane touches down nose-low or in a poor landing attitude, causing the nosewheel to strike the runway first and rebound the airplane back into the air, where it then descends nose-low again and repeats the cycle with increasing severity.
Plain English
A bouncing landing where the airplane rocks up and down on its nose and main wheels, getting worse with each bounce, like a porpoise diving in and out of the water.
Context Anchor
Encountered during landing training, especially in discussions of bounced landings, improper touchdown attitude, and recovery from landing errors.
Derivation
Named after the porpoise (a marine mammal related to dolphins) because the airplane's motion looks like a porpoise repeatedly arcing in and out of the water nose-first.
Why Pilots Care
Left uncorrected, porpoising can produce a propeller strike, runway excursion, or loss of control on landing.
Analogy
It is like a shopping cart with a bad front wheel that starts bouncing harder when pushed faster; if you keep forcing it, the motion gets worse instead of better.
Grounding Statement
Picture the airplane touching down, bouncing, then pitching nose-down and nose-up in a repeated cycle instead of staying settled on the runway.
Intuition Check
Porpoising does not mean a normal bounce or a smooth landing flare. It means a repeated, unwanted nose-down/nose-up motion that can get worse if mishandled.
Example Sentence 1
The student touched down nose-first, and the airplane began porpoising down the runway before the instructor called for a go-around.
Example Sentence 2
The instructor told the student to apply back pressure and go around when porpoising started on touchdown.