Q-Aviation Q64RI01 Explosion Proof TD/PM System D21+

A pilot landing on an offshore helideck at night is aiming at a painted circle they cannot see. The touchdown and positioning marking - the yellow circle, with the H identification inside it - is what defines where the aircraft should sit, and in daylight the paint does the job. At night, or in poor visibility, it has to be lit.

The TD/PM system does that by building the marking out of light rather than illuminating the paint. Q-Aviation describe it as Circle and H lighting comprising a concentric circle of at least 16 discrete lighting segments, superimposed on the yellow painted marking, together with the lit heliport identification marking. The result is that the geometry the pilot is flying to is visible as itself: a circle of the correct diameter in the correct place, not a floodlit approximation of one.

Segmented construction is what makes that work and what makes it survivable. Sixteen or more separate segments mean the circle reads as a continuous shape from the air while remaining a set of individually replaceable units on the deck, so one failed segment degrades the marking slightly instead of breaking it. It also means the assembly tolerates a deck that flexes and gets walked on, which a single continuous fitting would not.

The D21+ designation refers to the helideck's D-value - the largest overall dimension of the helicopter the deck is designed for - so this is the configuration for decks sized at 21 metres and above. The circle's diameter is set by the deck, which is why the system is specified per deck size rather than sold as one part number: a circle of the wrong diameter is worse than useless, because it tells the pilot the deck is a different size than it is.

Being explosion-proof is a requirement rather than an option here. This equipment is installed in the deck surface of a hydrocarbon facility, in the open, and it is walked on and washed down. It is controlled as a group from the helideck control system - in Q-Aviation's range the WEX4 and WEX5 control systems carry dedicated groups for the TD/PM system alongside the status light system - so the marking is switched with the rest of the helideck lighting rather than separately.