Nor do I;
reading the follow on posts, here is some physics for pondering for the other posts....
Planes fly nicely unless they are either -
- commanded to do something else; or
- upset by external factors; or
- the fundamental stability of the toy gets upset.
A plane that is happily bumbling along at 1.0g doesn't suddenly decide to go to 0.3g. the trim solution is to an angle of attack, and it is not going to have a large excursion from that to some other value just because the autopilot decided to turn off. If the autopilot elected to enter a wild ride, then as long as the autotrim function is running the plane will happily retrim to the new angle of attack and do what the errant autopilot computer is commanding. The plane continues otherwise doing its short period or long period oscillations around the mean trim alpha. Yaay. has been like that since Wilbur and Orville decided that the world needed flight attendants to make it a more palatable life.
A pilot pushing on the prong will drop the nose, as long as he (or she, but most she's are not stupid enough to do what the boys do) is pushing. As soon as he (or she) lets go of the input, the plane is going to revert to the trimmed alpha, and it will do a recovery all on its lonesome. Not just nice to have, it is a mandatory design requirement, even for unstable designs, the 1's and 0's have to be able to guarantee that is always the case.
getting to a seriously nose low condition takes a lateral excursion in order to occur unless the tail has gone its own way, and as was previously mentioned, with Lauda 004, "Mozart?" when the inadvertent thrust occurred on an engine in the mid climb, the PW4060 issue resulted in a huge disruption of the flow over the wing section immediately behind the nacelle, and that caused a large lift loss as well as yaw. As the aircraft rolled from the loss of lift, and from the secondary effect of the yaw, eventually the structure got to a point of exceeding the strength of the tail and the tail failed, by memeory with an asymmetric failure of the horizontal stab/elevator and then complete failure of the vertical stab, whatever, shortly thereafter, from the loss of the horizontal stab, the Cm from the wing and the CG shift of losing a stack of weight at the tail resulted in a rapid pitch down, that ended up with an overload of the main wing from an excessive negative g loading, after which the wings departed, and what was left was not much at all. A full on failure of the tail usually ends with the sky filled with chaff, an inflight breakup is almost always the outcome. JAL103 was an exception to that.
An aircraft that has a lateral upset is the most common means of getting into a nose low attitude. This can be from curious causes, Silkair being one, or the Classic loss out of Jakarta last year with the autothrottle clutch pack issue, or from entry into turbulence, or from instrument failures, like Stansteds B747-200F loss, or Adam Air with the INS's attitude being reset in IMC... that'll do it every time. When the aircraft rolls to a high bank level or inverted, the longitudinal stability will tend to drop the nose as the plane enters a spiral at high bank angles or tries to do a split S if inverted. The planes stab trim doesnt need to be altered and the outcome is a degrading flight path. What doesn't happen is the plane going to 0.3 g or other, it is trying to get back to the trimmed alpha, and that means it will tighten at the high bank angles, so g loadings increase. Tracking data if it is reasonably high resolution may show that a track change has occurred, but getting the nose down without changing the trim needs the roll.
On the morning of this accident, I was planning a medevac into China for the following day, and the plane involved had a recent radar issue that had resulted in a radar swap. As part of the planning, I looked at the weather in southern and eastern China, about 4 hrs before the accident and there was convective weather forecast near Guangzhou and to the west, and otherwise the area was quite clear. tops above FL260 were not significant except in that area, and the lightning strikes were being displayed in that area, then next closest area was over Pusan/Pohang and south of Vladivostok.
The grounding of 200 plus B738s seems to be premature. Unless there is clear evidence of a stab tab or other item falling off around the top of the drop, there is not much likelihood int his case that a structural failure was involved. Parts that separated part way down were unlikely to be the cause, they are the consequence.
Having said all of that, occasionally stuff really is surprising. I recall one investigation where the crew got 12,500FPM upwards, busted the assigned altitude by 4000' topped out at 0.2g, and then got 12000FPM on the down side and busted the assigned altitude a second time for good measure. The pull up was 1.3g, the over the top was 0.2, and the pull out was 1.3g. That got a spot on the wall, for the rest of the day until the next incident surpassed it. During the rollercoaster, the Captain managed to complete the full multi language PA to the passengers welcoming them on board and thanking them for choosing to fly brand X. The FO has the misfortune to be in a spritely climb in a light plane and to encounter an entry into a jetstream that increased the headwind by well over 100kts over 4000' and he elected to stay in FCLH targetting Mach.... so the latter climb was all done with the thrust levers at idle, and one very confused FO. The cabin crew continued their excellent, long suffering service, and didn't leave any dents in the ceiling.
TBs maths is OK for a wings level entry, using a dFPV/dt, V input, to determine a g loading, but anything that achieves that in a wings level condition is a seriously catastrophic event, the fact that the aircraft had any reduction in the severity of the dive angle suggests it was still responsive to control un until the time it then wasn't. 73 drivers don't often do push overs, recall that they drivers are sitting a fair arm forward of the CG, and the rate of pitch needed to go to zero g gets the drivers up close and personal with the fuel panel and the pressurisation control panel unless well strapped in.
Pushing to zero g and holding it for any time is a good push on the prong, gonna get tired doing that for long, and to hold it, without running the stab trim, that is a big ask