Hello again everyone,
I read your posts carefully, yet still I see no trouble, please help me understand where the percieved dilemma comes from.
Typically (think of alternate aerodrome planning minima..), there are dispatch conditions, which are more restrictive than what is in fact operationally required to land. Then:
You can land safely if ALD (actual landing distance) is less than LDA - in flight calculation requirement. To put some margin in, the regulations require us to use ALD*1,6 coefficient
in the dispatch phase. Thus: a) on purpose we dramatically reduce the statistical probability of really needing to land at ALD=LDA; b) if WX/MX/ conditions change unpredictably whilst airborne, the pilots are still allowed to use the full certified capabilities of the A/C without the 1,6 margin restraining them.
The NORMAL situation
1) big margins needs to be applied to dispatch
2) once in flight, as long as ALD < LDA, you may land "WHATEVER".
(statistical approach to hazards and risks)
I understand (f1) correctly, it provides - for a specific set of conditions - a waiver to the principle above:
So the ALTERNATIVE situation
1) the big margins normally in force (dispatch requirements) can be circumnavigated
(2 alternates et al.)
2) but only if you promise to adhere to them before starting the approach. Which is not normally the case required.
To summarize:
A) The regulators ask us to use a hazard filter (ALD*1,6 at dispatch), and then allow us to operate all the way to the limits (in-flight: ALD <= LDA) if the situation requires so.
B) The regulators via (f1) allow us to
depart with special provisions (two alternates) without the 1,6 "hazard filter" applied yet, but we still need to show compliance before commecing to land.