The Garuda 737 Accident

In the 08 March Garuda 737 accident, passenger and witness descriptions of their perceived sequence of events, indicates that the nosewheel was "driven in" in a potentially catastrophic nosewheel first touchdown and that a destructive PIO called "porpoising" then began. Porpoising can become a divergent phugoid in a jet that's landed far too fast for its weight (and with insufficient drag flap).
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What's Porpoising?
After the nosewheel oleo rebounds upwards and the aircraft "bounces" (courtesy of the MLG oleos decompressing a short time later), the neophyte pilot's natural tendency is to instantly lower the nose and again "spot the deck" (i.e. try to force the airplane onto the ground). It's completely opposite to a normal flare and hold-off process. The inevitable result is another nosewheel first strike (and rebound). The PIO is underway......
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This apparently happened three times and on the third occasion the nosewheel oleo snapped off (thereafter no hydraulics, no nosewheel steering, no directional control via rudder, no reverse and MLG braking only from the brake accumulator - about five applications before it's empty).
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Complicating matters in turboprops and piston-engined airplanes is the instant power response that's available (i.e. pilots can easily get "out of sync" by adding power in the bounce [i.e. on the rebound]). That added power cycling tends to "eat up" runway remaining. However to achieve the same porpoising effect in a jet, you just have to be "hot" (and high) over the threshold, have little or no flap (i.e. drag to kill off your float speed), try to force the airplane onto the ground (resulting in a tricycle landing or even worse, striking nosewheel first).

Adding to these self-wrought woes is the fact that any power "adds" (or throttle manipulation) will inhibit spoiler extension and add to the overrun likelihood. Even without throttle jockeying, you still need the MLG squat switches to be depressed long enough for the spoiler panels to pop up (and then of course, the oleos to remain depressed). During porpoising that just won't happen so, lacking that spoiler effect, the wing just keeps "flying". It's a PIO cycle that's destined to end up destructive and/or off the end, particularly if you're hot and have landed much too far in. We can expect to see many more of these types of "mishandling, confused and fixated" accidents the world over - as pilot experience levels drop (and the new MPL licencees move up in the airline world).

This theory may explain the underlying cause for Flight GA200's fate once they'd touched down. But why did they allow the aircraft to get so "hot" (i.e. fast) on finals? It may be that the RH seater just neglected to select flap (or only took 15 degrees and then totally forgot about the flap lever because of the distraction of a wind-shear/microburst and overshoot trend). If they flew through a sharp gust or thermal and picked up a temporary tailwind and just lowered the nose to correct the overshoot trend? Well that would just indicate a fairly inept handling of a common everyday problem. Unless there was some other complication, put it down to an inability to cope with the environmentals - and perhaps the relative inexperience of the RH seater. The captain was actually quite experienced, but probably let it all go too far. Porpoising is a PIO - and by definition it can be a self-sustaining destructive process. Pilots aren't taught about porpoising in any syllabus, so their first encounter with it will be an eye-opener. And fixation (leading to task saturation) is by far the most common cause of mishandling accidents during the landing evolution.
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For some examples of porpoising, try this link