Only the Captain can really answer that.
My totally unfair speculations (but based on available NTSB data):
1. Prior to the approach, the Captain fixates on landing distances. This was due to some weather expected in the area (rain, tail winds during approach). The crew enters "wet" runway for their landing distance computations, and saw that the standard "Autobrake 2" setting isn't going to cut it. They set Autobrake 3, and the Captain also elects Flaps 40 for extra margin. This is her mindset coming in.
2. Near touchdown, the FO hand flies by reference to PAPI, while the Captain looks through her Heads-up Display (HUD) -- probably in IMC Mode, with ILS RWY 4 showing on the display.
3. The problem is, at LGA RWY 4, the ILS glideslope and the PAPI are not coincident. The PAPI is set "further down" the runway, so even if you fly perfectly down the PAPI, you would show increasingly high on the ILS GS. At the threshold, the airplane would be 54' high if on the ILS, but would be 76' high if on the PAPI. And we all know that the ILS by design gets really sensitive near the runway.
4. On short final the FO goes a touch high on the PAPI and is slow to correct it. He maintains the required descent angle (3.10 degrees), but on the Captain's HUD ILS it looks like the plane is "ballooning" when in fact it is not -- causing a type of spatial disorientation. In fact, from the HUD perspective, the plane looks like it's going to fly "well past" the TDZ -- where the ILS GS intersects the ground. (Which it was, since the PAPI is set further down the runway).
5. On the HUD ILS the plane looks like it's increasingly high and the Captain overreacts. She chops the throttle and takes over the controls from the FO, at less than 75' AGL. The ILS glideslope is now at full deflection too high (5-dots) -- even though the approach is fine on the PAPI. The Captain wants "to get down now", so she relaxes on the control column and lets the nose drop... and drop... and drop... chasing the already-past ILS glideslope.
6. Two seconds to impact, the Captain realizes her mistake. She starts to apply full-throttle but changes her mind -- and chops the throttles again to idle. BUT, she makes another mistake: the left engine throttle was not pulled back all the way. This creates a little asymmetric thrust.
7. The Captain thinks about pulling the nose up, but its already too late. Impact occurs with aircraft nose-down, no flare, and the nose wheel collapses. The plane is now sliding on the ground. Due to #6 above the plane starts to veer to the right of centerline. The Captain tries to adjust with rudder. Well into the slide someone notices the left throttle was still open and pulls it down to idle.
8. The plane finally comes to a stop. The Captain orders everyone to stay in their seats, but the flight attendants and jump-seat pilot notice smoke in the cabin. The Captain orders evac, but does not use the evac checklist.
Last edited by peekay4; 1st Nov 2014 at 18:28.