How does the pilot find the touchdown spot at night?
A circle of yellow lights on the surface shows where to place the helicopter.
The touchdown positioning marking (TDPM) is a yellow circle on the TLOF that shows the pilot where to position the helicopter. At night, TDPM lights light that circle so it can still be seen.
The circle is centred on the TLOF, with the white H at its centre, and its inner diameter is half the helicopter's D-value (0.5 D). The pilot places the helicopter so the pilot's seat is over the marking (over the circle itself, not its centre). That puts the whole undercarriage inside the TLOF and keeps every part of the helicopter clear of obstacles by a safe margin. The lights show one position, not the edge, so they are yellow and sit inside the green perimeter lights.
Show one spot on the surface: where to place the helicopter.
Show the edge of the touchdown surface. See Entry 2.
Frequently Asked Questions
Q1What are TDPM lights?
Lights that mark the touchdown positioning marking (TDPM) on the touchdown and lift-off area (TLOF) at night. The marking is a yellow circle on the surface, and the lights make it visible in the dark.
Q2What does the pilot do with the marker?
The TDPM shows where to position the helicopter. The pilot places the helicopter so the pilot's seat is over the marking (the circle itself), which puts the whole undercarriage inside the TLOF and keeps the helicopter clear of obstacles by a safe margin.
Q3What colour are TDPM lights?
The marking is yellow, and the lights that show it are yellow too, so the pilot reads them as the positioning circle rather than as the green edge lights. Confirm the exact light type against the standard in force.
Q4How is it different from TLOF perimeter lights?
The green perimeter lights mark the edge of the surface. The TDPM lights mark one place on it, the spot to position over. Seeing both tells the pilot where the surface ends and where to put the helicopter. The perimeter lights are in Entry 2.
Q5Does every heliport need TDPM lights?
No. The TDPM is a marking provided where the standard or the heliport design calls for it, and the lights are then needed for night use. Whether it is required depends on the heliport type and the standard in force, so confirm with the project specification.
Q6Which standards apply?
ICAO Annex 14 Volume II covers heliports, and national regulators publish their own requirements, such as the FAA heliport design advisory circular and the UK CAA's CAP 437 for offshore helidecks, which calls for a lit touchdown/positioning circle. Light count, spacing, intensity and the marking size differ between them, so confirm against the standard in force and the project specification.
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