What is a PVASI?
The Pulsating Visual Approach Slope Indicator. One light unit shows the pilot the slope by colour and by whether the light is steady or pulsing.
A PVASI is a visual slope indicator built from a single light unit, normally beside the runway. Instead of comparing two bars, the pilot reads one light by its colour and by whether it is steady or pulsing.
Above the slope the unit shows pulsing white. On the slope it is steady white (on some units the on-slope signal is alternating red and white instead). A little below the slope it turns steady red, and well below it the red pulses. The pulsing makes the two extreme cases stand out, so a pilot who is far off the slope is warned more strongly than by colour alone, and the pulsing rate increases the further the aircraft is above or below the slope.
Because it is only one unit, a PVASI is simpler and cheaper to install and to align than a VASI or PAPI. The trade-off is that the on-slope band is narrow and the pilot has to watch the light closely. Because it is a single light that could be confused with other lights, the pilot must take care to locate and identify the signal. It is therefore found mostly at smaller airfields, helipads and some military or private sites.
Frequently Asked Questions
Q1What does PVASI stand for?
PVASI stands for Pulsating Visual Approach Slope Indicator. It is a single light unit that shows a pilot a white or red light, steady or pulsating, to indicate where the aircraft is relative to the approach slope.
Q2How does a pilot read a PVASI?
Pulsating white means the aircraft is above the slope. Steady white means it is on the slope. Steady red means it is slightly below the slope, and pulsating red means it is well below the slope. On some units the on-slope signal is alternating red and white instead of steady white. The pulsing rate increases the further the aircraft is from the slope.
Q3How is a PVASI different from a VASI?
A VASI uses two or three bars of several units and the pilot compares the colours of the bars. A PVASI uses one unit, and the pilot reads the colour and whether the light is steady or pulsating. This makes it simpler and cheaper to install.
Q4Is steady white the only correct indication?
Steady white is the usual on-slope signal, but the on-slope band is narrow. A steady red light means the aircraft has started to drop below the slope, so it is a prompt to correct before the light starts to pulsate.
Q5Where is a PVASI used?
Mostly at smaller airfields, on helipads and at some military or private runways, where a single unit is enough. Exact siting, range and aiming come from the applicable standard and the manufacturer's data. A PVASI is not one of the visual approach slope indicator systems specified in ICAO Annex 14 (PAPI and APAPI, with T-VASIS and AT-VASIS), so check that the aviation authority accepts it before one is installed.
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