How do you choose a visual guidance system?
The short list of questions that turns the guidance a pilot needs into the right system to look at, always in the same order, so a requirement is never lost behind a preference.
The visual guidance decision flow is the sequence of questions asked, in a fixed order, when a runway or stand needs guidance by light. It joins together what the earlier entries compare: which systems show the approach slope, which do a different job, and how the PAPI, APAPI, VASI, PVASI and T-VASI differ.
The first question is what kind of guidance is needed. If it is not approach-slope guidance, the answer is docking guidance on the stand or runway lead-in lighting along the approach track. If it is, the next question is whether the standard, the project design or the installed base already names a system, and if so that system is used. Only then does size and scope decide: a small aircraft type or a limited scope points to the two-unit APAPI, and otherwise the four-unit PAPI is the usual choice.
The order of questions that leads from the need to a system. The same need gives the same starting point whoever asks.
Places the systems side by side: layout, how the pilot reads each one and the role it suits. The flow uses that comparison to choose.
- State the need. Say what the pilot must see: the approach slope to a runway, the track along an approach path, or the position on a stand.
- Ask about the slope. If approach-slope guidance is not what is needed, leave the slope indicators: use docking guidance or runway lead-in lighting.
- Ask what is specified. If the standard, the project design or the installed base already names a system, use that system.
- Ask about size and scope. A small aircraft type or a limited scope points to an APAPI with two units; otherwise a PAPI with four units.
- Confirm the choice. Check it against the standard and the manufacturer’s data, then design the layout, setting angles and alignment.
- Record the decision. Note the system chosen and the reason, so the next review starts from the same basis.
Frequently Asked Questions
Q1What is the visual guidance decision flow?
A short sequence of yes or no questions, asked in a fixed order, that leads from the guidance a pilot needs to the type of visual guidance system to look at: PAPI, APAPI, another slope indicator named by the standard or the site, or a system that gives a different kind of guidance such as docking guidance or runway lead-in lighting.
Q2In what order are the questions asked?
First, is approach-slope guidance needed? If not, the answer lies with docking guidance (on the stand) or runway lead-in lighting (along the approach track). If yes, does the standard, the project design or an existing installation already name a system? If so, that system is used. If not, does a small aircraft type or a limited scope point to an APAPI? If yes, APAPI; if no, PAPI.
Q3Why is the standard or site question asked before the size question?
Because a system that the standard, the project design or the installed base already specifies is not a free choice. Asking about it early stops a preference for one system from overriding a requirement, and keeps a new unit compatible with the equipment, spares and procedures already on the airport.
Q4Is every visual guidance system a slope indicator?
No. PAPI, APAPI, VASI, PVASI and T-VASI show the approach slope. Runway lead-in lighting marks the track over the ground along an approach path, and docking guidance guides the aircraft onto its stand after landing. Neither of those two shows the slope, so the flow sends them out at the first question.
Q5Where does the flow end?
At a confirmed choice. Every branch ends with the system checked against the applicable standard and the manufacturer's data before the layout, setting angles and alignment are designed. The flow shown here is an example; the airport's own procedures and the project design set the real criteria.
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