The Precision Approach Path Indicator, commonly known as PAPI, was devised by Tony Smith and David Johnson at the Royal Aircraft Establishment Bedford in 1974 and has been in use since the 1980’s.

Tony Smith will host our next FREE TMS Tuesday ‘Runway to Recovery Webinar’ discussing PAPI lights  and are they really aligned & serviceable? Click here to register.

PAPI is an ICAO Standard visual aid. The specification of the Standard and accompanying design guidance are published by ICAO in Annex 14, Volume 1 and the Aerodrome Design Manual respectively.

The signal of PAPI provides pilots with the accurate visual information they need to acquire and maintain a stabilised rate-of-descent on the specified glideslope throughout the final approach. PAPI is installed at many aerodromes where non-visual guidance is routinely used with an autopilot to control the aircraft. In these circumstances pilots have an independent cross-check on the functionality of the non-visual guidance and can safely continue an approach manually in the event of an autopilot malfunction or when the non-visual guidance is not in service.

There are many runways where non-visual guidance facilities are not provided. In these circumstances PAPI can provide guidance to enhance the safety of approaches.

If PAPI is to provide the specified guidance then all the specification details must be adhered to. There are instances in current practice where it would appear that this requirement is not met.  This Webinar will highlight these issues.

The signal characteristics of the PAPI must be fully adhered to. They are defined in terms of beam dimensions and intensity, signal colours, siting and alignment. The most important characteristic is the sharpness of the transition of colour and intensity as projected by each light unit in the PAPI array together with the correct elevation angle for the transition Unless these are in compliance with the original design the correct signal will not be displayed.

The white-over-red format of the light signal, including what, to, pilots appears to be an instantaneous change of colour and intensity at the transition must be provided. For design purposes a transition angle of 1 minute of arc as seen by the human eye is feasible. This angle should never be more than 3 minute arc at all operational ranges (> 300m)

It should be noted that both the signal colour and the intensity should change within the design limit. The intensity change (5:1) in the specification is an important part of what makes the change conspicuous. It is an error to equate the intensities of the 2 sectors. The intensity change adds an important apparent flashing characteristic.

The PAPI light unit should be treated as a device where the signal characteristics and alignment are built in during design and manufacture. Apart from light source replacements the light units should never be worked on in the field. The place for rectification and re-calibration is in a workshop or with the manufacturers. The light unit design should be such that the units can be installed at the correct setting angles using an inclinometer or equivalent.

However, light units and their setting angles can become out of alignment in service so it is important that the transition, the setting angle, colour, beam spread and intensity can all be measured in the field during installation, acceptance tests and at appropriate intervals in-service. Any measurement devices used for this purpose should themselves be regularly calibrated.

It is important to note that traditional flight checking is not adequate for the task of verifying that a PAPI system is meeting the performance criteria.

Learn all about PAPI Lights in our FREE Webinar hosted by Tony Smith.

PAPI Lights – Are they really aligned & serviceable?
26th April @ 1400 London time. This live webinar will last one hour including Q&A’s with our expert panellists.

Register your FREE place here.

All our technical training courses are in accordance with ICAO’s CBTA guidelines and for further information please visit the TMS Training Solutions website:
https://www.tmstrainingsolutions.com

We look forward to seeing you April 26th!