I agree with Ron on the timing as habit. 1 second as you cross an FAF/GS intercept to touch and verify the timer whether or not the specific approach required timing is a very small thing. You might be much more precise in your determination of whether or not to time, but I've seen an awful lot of pilots who primarily fly untimed approaches who almost always forget that tiny simple step when they fly a timed one.
I see that one as similar to whether you signal for a turn in a car on a deserted road at 3 am. I do. Create a habit. I got into an argument with a friend over it - he thought it was stupid and unnecessary. Some time later, I wrote as a passenger in his car. He =never= signaled for turns.
OTOH, I do =not= teach GUMPS in a fixed gear airplane (at least until the pilot also flies retracts) since I think it teaches that when you pay no attention to the gear, nothing happens.
Again, let me be clear -- my point about the timer is that it is being taught as a
requirement for ILS approaches --
it is not (as long as you have a means to determine the MAP, whether GPS or cross fix, etc).
What is also taught is that the timer will allow a seamless transition from Precision to Non-Precision if the GS fails.
In the Army we had a saying -- "Fight as you train and train as you fight."
When the feces hit the fan you will revert to
training, not some esoteric discussion in a pilot lounge. With all due respect to the authors of the FAA's
Instructor Handbook, practice to standard in realistic conditions assures task mastery (thus the FAA's (belated) adoption of Scenario Based training). Very often these tasks consists of a string of well developed habit patterns, certainly.
But the learner should be able to consciously explain
why he/she did X, not just perform mindlessly.
Primacy, effect,
et al all have a place, but we're training humans, not baboons. An example -- when my oldest was 6 months old we gave her peas for the first time. She had more peas on the floor than eaten. According to the Law of Primacy, she'd be bad company at a nice restaurant.
But over time, as skills developed and accuracy improved, the standards were raised and she achieved use of knife and fork.
In my own IR training I witnessed this first hand. My CFII insisted I tune Nav 2 to the ILS once established as a backup in case of the loss of Nav 1.
OK...
Until we flew an approach with cross radials as fixes.
I quickly learned
that rule was not absolute (even though my primary exposure was "Always tune a backup")
Thus
practice to standard under
realistic conditions is the trump card in training. All the rest support or detract from this goal.
Thus my point is that loss of the GS is cause for a miss, an evaluation of the cause of the loss of the GS, reflection/consultation, and
then a re-start of the entire procedure or flight to VFR conditions.