Hi there Nok,
I like your hint, or ‘rule of thumb’, it helps with a broad understanding of the importance of crossing the threshold at a sensible height.
For example, suppose before the approach you calculate a landing distance of 2000 m, while the runway length is 2250 m
If you’ve calculated your landing distance at 2000m then you are in a pretty fast and heavy aeroplane.
when you’re over the threshold and the RA shows or calls out “100”
I can see that the aircraft is quite sophisticated as well.
One thing I have noticed over the last few years is that when I’m sitting beside a person with relatively low flight experience, ( say 2000hrs) and we are crossing the threshold of the landing runway, they could do a nice job of the landing, and they could tell me what 3x7 equals, but they couldn’t do both at the same time.
When you are crossing the threshold it isn’t the time to try and determine your deviation from the 50 foot ideal and then make a simple mathematical calculation, and then use the answer to make a decision about whether to continue to land or conduct a missed approach. It’s simply too cumbersome.
But that is no problem because on 99% of landings in a big fast sophisticated aeroplane, you will have markings painted on the runway that give you good information about your runway performance. Most of the time you don’t want to touch down before the 1000 foot markings, you’d be fairly comfortable with touching down at the 1500 foot markings, and you’d be a bit disappointed in yourself if you landed on the 2000’ markings. Beyond the 2000 foot markings we are starting to get into more nuanced decision making conversations that will differ for each weight and each runway.
So although I like your rule of thumb regarding threshold crossing height, I think it best serves pilots as an easy way to articulate the importance of accurately flying the planned approach profile while they are sipping coffee in a classroom, and could be problematic if applied in real time.