Just seeking some perspective on the timing of the events, all values approximate with many assumptions.
Standard approach at 200 ft/sec (120 kts average GS), ROD 600ft/min; time to threshold from 2nm (12000 ft) ~ 60 sec, flare 10 sec from 50 ft.
- With unresponsive engines at 600 ft:- worse case (no thrust) in this class of aircraft, might (IMHO) result in 9 deg glide path (1800 ft/ min 30 ft/sec), but this is not achieved instantaneously and probably not achievable at all before a flare would have to be commenced at a much earlier height than normal (20 sec or less to ground contact) – not the case.
- With reduced thrust (flt idle), a 6 deg glide path (1200 ft/min, 20 ft sec) might be expected, but again not instantaneously (30 sec to ground contact) - unlikely.
- A more reasonable scenario is a slightly reduced thrust setting, that used for deceleration from 160kt to stabilize at Vref, thus a thrust increase would be required before 500ft, but the thrust change was not obtained (engines unresponsive).
Accident geometry:- Touchdown ~1200 ft short of runway. Thus, distance traveled during the period of reduced thrust 12000 – 1200 = 10800ft. Which at 200ft/sec (no significant speed reduction until the flare) takes 54 sec.
Flare time 10 sec from 100ft (assume 100 ft flare commencement height in a reduced power condition – reducing to Vs), thus 500ft altitude loss in 44 sec gives an average descent rate of ~ 11 ft/sec. This ‘modest’ value might be due to initially trading airspeed for descent rate (height).
N.B. this does not equate to, determine, or otherwise infer the touchdown ROD.
The perspective:- Many viewers will take 44 secs to read this post, some will take longer particularly if they attempt to understand ‘the situation’ (calculations), which involves higher mental workload.
Whatever the cause of the problem, this perspective indicates why the crew did such a good job.