Back to basics
One reason for the extensive technical discussion in this section is that the basic principles of low visibility operations are being lost. The example quoted on the opening page of this section, from the website of a highly respected training organisation, is typical and illustrates why traditional PF/PM procedures contain significant risks that PicMA procedures eliminate.
Just to re-iterate, it suggests that when using traditional procedures in low visibility, even if the PM has called "lights in sight" at DH, the PF should "wait until the PNF calls out "Runway in sight, ? o'clock position" before going visual".
The core of this recommendation, to maintain instrument flight for as long as possible, is 100% sound. It also goes some way to following the NTSB recommendation about limiting sighting callouts to those visual cues which are "associated with the runway environment". But in detail, it shows a misunderstanding of the very definitions of the minima.
A decision is required AT Decision Height. This decision is not about what the PM/PNF can or cannot see. It is whether the pilot who will actually be doing the landing has already seen enough of the visual aids or approach area to complete an assessment of the aircraft position and rate of change of position, in relation to the desired flight path.
Decide!
At DH the pilot landing must DECIDE whether or not the aircraft trajectory is satisfactory for landing. Unless the answer is "YES IT IS", further descent is not allowed. The regulations assume that this is what will happen when setting DH/RVR minima for each approach, and the entire safety system in these circumstances rests on it being done.
To take the example case quoted. It has already been established that the aircraft is on the optimum INSTRUMENT trajectory: "the PF shoots a picture perfect ILS! Both needles are crossed right down to Decision Height!.) At 200ft (DH) "the PNF called "lights in sight". The PF looks up, away from his instruments and sees nothing but an array of white flashing lights. He gets vertigo (spatial disorientation), loses control of the aircraft, and balls it up in the approach light array".
So what has actually happened in this example? At DH, the PF has NOT HAD TIME to assess the flight path BY WHAT HE CAN SEE of the external cues. He needed to do this because even a "picture perfect ILS" may not be on the correct trajectory relative to the ground - and it may not have been a "picture perfect" ILS to start with. Assessment takes at least 3 seconds, and he did not even start until they had reached DH.
The solution advocated is that the PF should not even look up until the PNF calls that he has the RUNWAY in sight. But in classic Cat. 1 visibility minima conditions, e.g. 200ft DH and 550m/1800ft RVR, the runway cannot be in sight at DH. The aircraft is 3000 ft / 900m from the runway threshold in 550m RVR.
It is unfortunate to have to say it but what is being advocated is in reality an attempt to be a bit safer when "busting minimums".
The well-meaning advice to ""wait until the PNF calls out "Runway in sight, ? o'clock position" before going visual" actually means one of two sequences must occur.
EITHER: At 200ft the PNF calls "Minimums" (or "DH", "Decide" or whatever SOP wording is in use), "Lights in sight". According to the DH definition, the PF must now respond "Go-Around", because he has NOT had "the visual aids or the approach area in view for sufficient time to have made an assessment of the aircraft position and rate of change of position, in relation to the desired flight path", let alone decided whether it was satisfactory. But clearly this is not what the advice intends.
INSTEAD, it recommends that at 200ft the PNF may call "Minimums, "Lights in sight". But the PF should wait until the PNF calls out “RUNWAY IN SIGHT, ? CLOCK POSITION”, before going visual. That means "PF should continue on instruments BELOW DH". The PF must ignore the DH, and wait until until the PNF calls out that HE OR SHE (the PNF) can see the runway - if he ever does.
By definition the aircraft will now be significantly below DH. The PF looks up and will take a minimum of 3 seconds to assess the flight path, during which time the aircraft descends a further 30 feet. With luck the aircraft's trajectory ("position and rate of change of position") is still good, and the PF is able to land successfully.
But it may not be, because of for example, control inputs or environmental factors such as wind changes. Then either a go-around will be needed from considerably below the minimum altitude at which obstacle clearance is assured, or if the landing is continued a runway excursion or other unsatisfactory outcome may occur.
This scenario is exactly what has happened in many accidents, such as that in February 2007 at Cleveland Ohio. Approaching DH, the PM/PNF has called that some visual cues exist, and the PF has then continued below DH, expecting to see enough to land, while the PNF also continues to look for visual cues. Neither has adequate visual information and neither is adequately monitoring the instruments - the exact hazard identified in the NTSB special study of 1976, and a prime reason for the initial development of "monitored approaches" in the 1960s.