On reflection, #24 was glib - conceptual rather than absolute. There are few if any absolutes in aviation.
The concept of ‘
use it all’ is similar to the mindstates of ‘how can we land’ vs ‘should we be landing’ in a pre-landing assessment. The objective (the latter) is to encourage crews to be aware of the assumptions in landing performance and thus the limitations of their landing decision.
Many overrun accidents involve misjudgments of the conditions or a poor choice of action. If these occur in combination with large, but normal variations of operating performance – unstable approach, high over threshold, landing fast, long, delayed deployment of spoilers, etc, then the risks of an overrun increase rapidly.
It should be possible to identify these risks and mitigate them before landing by deciding to change the planned level of braking and/or use of full reverse – a strategic decision. Any later identification of the need to change plan involves a ‘tactical’ assessment and is often complicated by time/workload pressures. This assessment often occurs when well down the runway, and approaching or exceeding the point of being able to prevent an overrun.
Certificated landing distances are based on the use of max braking with an added distance safety margin (factor). This margin “
accounts for the normal operational variability that can be expected in day to day service such that the chances of a landing overrun are remote” (
Landing Performance Large Transport Aeroplanes ).
Thus if landings were routinely made at the limit of pilots’ variability, and on limiting runway lengths, max braking would be required to minimize the risk of an overrun to a chance less than ‘remote’.
Fortunately most pilots constrain their variability, and in general do not routinely land on limiting runways (ex LCY etc). However, this apparent normality in operation can lead to complacency.
Using the concept of max braking can minimise any additional risk from complacency, unexpected variability, misjudgement, misassessment, or poor plan of action. When a landing decision chooses not to use max braking, crews should have an improved awareness of the associated risks and mitigations for that landing, i.e. the crew thought about them before changing the ‘sop’ (max braking standard operating plan) to an acceptable alternative.
Brake for safety not for comfort.
Reverse is not normally considered in certificated landing performance due to reliability / consistency problems (CS/FAR 25.125).
If crews assume that the safety of a landing could be maintained by ‘late’ use of max reverse, based on their assessment of the situation, then there is some (significant) risk that reverse might not be available/used when required – and at a time/position on the runway where it would be effective.
Here, the concept of planning to use max reverse (‘sop’) can reduce these risks by checking that the ‘emergency late use’ of reverse will be available – that the system has deployed and the engine has spooled up immediately after touchdown. If reverse does not work, then braking can be increased much earlier to minimise the risk in the event of other problems – as above.
Use of reverse vs environmental impact should be considered as a separate, but important safety issue of conflicting goals and objectives. See refs to ETTO - efficiency / thoroughness tradeoff.
The frustrating point is that local authorities duck their responsibility for safety by placing the decision on operators and pilots.