P.A.P.I. Maintenance Q&A

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 manufacturers 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.

6/20/2014 AC 150/5340-26C

Table 5-9. Preventive Maintenance Schedule for PAPI (Precision Approach Path

Indicator)

Maintenance Requirement

1. Check lamps for operation. X Daily

2. Check operation of controls. X Monthly

3. Check for damage by service vehicles or aircraft. X Monthly

4. Clean lamps and filters. X Monthly

5. Check mechanical parts for damage. X Monthly

6. Check lightning arresters. X Monthly

7. Check for water damage or insect infestation. X Monthly

8. Check for presence of rodents. X Monthly

9. Record output current and input voltage of adapter

(if used). X Monthly

10. Check alignment and aiming of light boxes. X Monthly

11. Check leveling and operation of tilt switch. X Monthly

12. Check integrity of obstacle-free approach plane. X Quarterly

13. Check insulation resistance of underground

cables. X SMANY

14. Check resistance of grounding system. X SMANY