Design
A typical engineering design specification for a PAPI light unit is shown below;
Optical construction:
- Preadjusted 2-lamp optical assembly.
- Anodized aluminium reflectors.
- Red colour filters.
- Precision-ground lenses.
- Lamps and reflectors replaceable without recalibration.
- 2 x 200 W / 6,6 A prefocused halogen lamps, Pk30d base.
- Average lifetime 1000 hours at rated current.
2008 saw the advent of new PAPI devices manufactured using solid state LED lamps instead of incandescent lamps. The LEDs produce sufficient brightness to satisfy ICAO light intensity and beamspread standards, and average lifetime with the LED based systems is 50,000 hours or more. By using LEDs the power consumption is lowered considerably. The LED systems run internally on DC voltage so the DC voltage requirements, along with the LED's inherent low power consumption, now allow for solar-powered PAPIs, completely removing them from the power grid.
The PAPI system is co-opted for use by the final approach runway occupancy signal (FAROS) system being introduced at several major airports in the United States for the purpose of allowing pilots to resolve a runway incursion without requiring a priori notice of an occupied runway from the control tower. In FAROS, automated line-of-sight runway sensors detect if a vehicle has committed a runway incursion and if so, will flash the PAPI lights to alert the pilot of an aircraft on final approach that the runway is currently occupied. The pilot then becomes responsible for resolving the conflict by notifying the air traffic controller and executing a go-around. Once the tower has ascertained that the runway has been cleared, the ground controller resets the PAPI so that landing operations may resume.
Read more about this topic: Precision Approach Path Indicator
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