Aim Point Comparison Calculators for True Professionals
Aim Point Comparison Calculators for true Professionals
Embedded within the Jacobson Flare App are 5 bespoke calculators. Two are designed to calculate the longitudinal Aim and Flare Points for both heavy and light airplanes, respectively. These provide a major component of the Jacobson Flare approach and landing technique.
However, the JF App for iOS also contains three specially-created calculators. These enable accurate comparison of the correct visual aim point for any given airplane, with the aim point defined by the geometric specification of the three most common electronic glide path systems, namely ILS, PAPI and the Australian-designed but sadly obsolescent T-VASIS.
As an example, the PAPI is a virtual point source, providing a 3° ± 12’ design eye path to just one aim point. There is no standard MEHT.
Since the PAPI is generally installed to suit the largest airplane type operating into an airport (often B747/B777), many MEHTs are of the order of 71- 75ft, with corresponding aiming points of approximately 1500ft (450m). This makes many PAPIs unsuitable for narrow-body transport jet operations, let alone executive jets, prop jets and other charter airplanes, which have aim points generally around 1000ft (300m). Some sort of correction – or compromise – is necessary; but what kind and when?
In that instant of realisation – during the approach – that the 2 aim points don’t align and confusion occurs?
Or pre-flight, with an accurate aim point calculation for each of your networks’ destination and alternate runways safely stored in your personal Aim Point Comparison database?
As an example, on a level runway, for a 3° PAPI to suit the B737/A320 visual aim point of 1000ft (300m), an MEHT of approx 50 ft would be required. (1000ft divided by 20).
Accordingly, it is sometimes impossible to satisfy the twin requirements of flying both a PAPI on-slope indication and an accurate 3° eye path to the correct aim point for the airplane type.
Another significant factor is that published MEHT data does not consider the runway slope. Downhill slopes, especially, have a profound effect on the siting of PAPI installations, in satisfying a specified MEHT. They are considerably deeper than those on level runways or, indeed, uphill-sloping runways.
The PAPI Aim Point Calculator (along with those for the ILS and T-VASIS) in this Reference section, accommodate the runway slope and other factors in their comparison with nominal visual aim points.
Cast your eyes over this example: The standard B737 visual aim point is 1000ft/300m from the approach threshold. On this runway, the MEHT is 74ft. This would place the PAPI aim point at 1513ft/461m – if the runway was level. Even this would be 513ft/156m deeper than the correct visual aim point, which is ‘King’.
However, this runway is not level – it has a downhill slope of -0.9% – and this would place the PAPI aim point at 1874ft/570m – 874ft/270m deeper than the correct visual aim point, at 1000ft/300m.
We commend these calculators to any and every professional civil and military pilots, even if you are not (yet) using the Jacobson Flare as your standard landing reference technique. The comparisons made available through our calculators will open your eyes – considerably – and answer every question you ever had about why your visual aim point never matched the secondary electronic slope guidance systems! Now, it can all make sense; and you can easily create your own database for future reference.
You’ll find these Aim Point calculators – and so much more – in the Jacobson Flare apps.
Wishing you many safe landings
Captain David M Jacobson FRAeS MAP
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