by Casey Carlson
MnDOT Aeronautics, Airport Electrical Administrator
Published in Midwest Flyer Magazine February/March 2023 Digital Issue
Precision Approach Path Indicator (PAPI) lights at an airport are a very important navigational aid. They are the type of navaid that a pilot might not utilize on a bright sunny day, but on a foggy or snowy day, PAPI lights can be essential.
From the maintenance perspective, can maintenance personnel just “set it and forget it” when it comes to PAPI lights? The short answer is, “no.” The FAA Advisory Circular 150/5340-26C establishes maintenance intervals for PAPI lights and provides direction to maintenance crews on how often PAPI lights and their components need to be checked. If an airport’s PAPIs are not being periodically checked, they can begin to stray from their intended angles. When PAPI lights stray from their intended angles, they could give bad information to a pilot on final approach. That’s why it’s so important for airport maintenance crews to keep PAPI lights adjusted properly for pilots. A pilot is expecting the PAPI lights to either be set correctly or taken out of service.
What type of issues does an airport manager or maintenance personnel encounter? Let’s look at some common questions that MnDOT receives about PAPI lights:
How often does airport staff have to check a PAPI to ensure that it’s sending the right information to a pilot?
For this answer, let’s look at the chart from Advisory Circular 150/5340-26C
Does the FAA require a flight check at the time of commissioning?
FAA JO 6850.5D states:
(a) A flight inspection is not required for VASIs and PAPIs used for VFR approaches only.
(b) A commissioning flight inspection is required for a new VASI or PAPI associated with an instrument approach procedure.
For PAPIs with associated instrument approach procedures, are the PAPIs ever required to be flight checked again after the initial commissioning has been carried out?
The short answer is, “yes.” FAA JO 6850.5D specifies several reasons that a restorative flight check would be required. A couple (but not all) of the reasons for a restorative flight check would be:
(a) When a PAPI fixture has been physically relocated.
(b) When the reference angle is changed due to an obstruction. An example would be a construction crane at a nearby jobsite which infringes into a clearance area.
What causes PAPI systems to fall out of adjustment and shut off?
PAPI systems can come out of adjustment for any number of reasons. Obviously, any time that anyone accidentally strikes a PAPI fixture with a mower or snowplow, there is a large risk of knocking them out of adjustment. In Minnesota, the most common need for an adjustment is the mere fact that the ground moves a lot in our state. The freeze-thaw cycles can move concrete piers that are large and deep in the ground.
What is the proper procedure for checking angles and adjusting PAPIs?
The best advice for adjusting PAPIs is to not make adjustments unless you are sure that you understand the process. Take the time to read through the manufacturer’s adjustment method so that you perform the adjustments properly. Alignment methods differ from brand to brand. For the most part, the instructions are available online at the click of a mouse. If you follow the manufacturer’s procedure, you will have the PAPI fixtures aligned properly in short order.
An experienced pilot has stated that the PAPIs “seem off.” Does the pilot know what they’re talking about?
Input from pilots should never be ignored. Pilots use many different instruments, and their years of flight experience preparing to land their aircraft are invaluable. Anytime a pilot provides feedback about how your airport’s PAPI system is operating, take your alignment equipment out and check it all out. Remember that the next pilot might be relying on the accuracy of the PAPI for their landing.
Any advice for airport managers?
MnDOT encourages all airport managers to take their PAPI aiming equipment out and measure the angles of their airport’s PAPI fixtures. However, don’t plan to make any adjustments until you are aware of the process; but do try out the equipment, and as questions arise, learn. The practical experience gained will provide understanding of the equipment and some insight into what is required when it’s time to realign those angles.
