In May 2026, a United 767 heading into Newark ended up clipping a post, which fell onto a truck. Here’s the preliminary report if you want a read.

The incident has sparked a bit of a debate over following the PAPIs, so I thought I’d take a little look at how they work, and what we maybe need to be a little cautious about – because there is a bit more to them than just a couple of reds and a couple of whites, and understanding what it is actually telling you, and what it isn’t, can be quite important, particularly when thinking about ‘going visual‘.

2 reds, 2 whites, everything’s alright!

Many pilots assume that a PAPI simply represents the glidepath for that runway’s approach, which in most standard cases is 3 degrees. So if we’re heading down an approach with a 3 degree glideslope, then when we look outside, we should see two reds and two whites.

This isn’t an “incorrect” assumption – PAPIs were, in most cases, set up to fit alongside the ILS, so when you stop looking in and start looking out, you have an additional ‘tool’ to support you in maintaining the right profile to touchdown.

Additionally, if you’re flying a visual approach, then they will guide you down on a standard 3 degree, which is what we like, and if we’re flying into a bit of a ‘black hole’ at night then they are doubly as useful.

But, simply going from inside to outside might not always put you in the right place. So why, not?

Number 1: They aren’t always where they say they are

Let’s stick with our old favourite, the ILS (CAT I) approach for now since we are all pretty familiar with these. The glideslope brings us down a precise path, using lobes and things, and then at some point we transition to the visual bit where we land.

The idea is we shouldn’t have to change the vertical trajectory when we go from looking in to looking out. We want to maintain the lovely, stable, vertical trajectory we’ve spent the last few minutes establishing, because then we have much more chance of a) touching down in the right place and b) doing it in a smooth, controlled way.

Depending on when you transition to visual though, it may or may not line up perfectly with the PAPIs. First up, transition at around 200’ and the PAPIs tend not to be accurate anymore, or rather – they can be too accurate. Like the ILS, they effectively create a cone, which means that when we are close to the runway (and the tip of the cone) the smallest of pitch changes can lead to you shifting out what is now a very narrow ‘path’.

A few feet high up will still keep you on two reds and two whites, but close in, and they will probably flicker from white to pink to red. So at this point, simply looking out and aiming for the planned touch down point is your best bet rather than trying to follow the PAPIs to touchdown and correcting for all that flickering.

Have a read of this:

“When siting PAPI on a runway with an established electronic glide slope, the PAPI visual approach path should coincide, as much as possible, with the one produced electronically. To accomplish this, the PAPI is placed at the same distance from the threshold as the virtual source of the electronic glide slope within a tolerance of ±30 feet (±10 m). The PAPI is aimed at the same angle as the electronic glide slope.”

What this is telling us is that, while more or less in the same point, they aren’t always at totally the same point.

Remember what we said about the cone? If you transition from ILS to PAPI fairly late, then there might be be a bit of a “pinkish” difference one way or the other. In this case, if your approach has been completely stable and on profile all the way down, then avoid big pitch changes trying to establish on the PAPIs and instead maintain your stabilised path, and aim at your aiming point.

But this is for the ILS, which as mentioned, the PAPIs are generally designed to sit alongside. What about if we are flying a different approach. Something GPS based like an RNP or a LPV?

Number 2: The non-ILS issue

GPS based approaches are based off generated ‘points in space’ rather than relying on signals sent from the ground – the ILS “lobes”. RNAV approaches are considered a little less accurate than ILS, LPVs basically as accurate.

But they work differently, and without getting into the nitty-gritty, barometric factors, temperature, obstacle clearance differences etc etc all mean the GPS calculated glidepath might not bring you down to the exact same point as the ILS antenna does, and if not, then those PAPIs which have been set up for the ILS might not work quite so well for your non-ILS approach.

Honeywell have a whole thing on this which is written much better than I can (and covers some of what I already said in more technical detail).

Long explanation short, when you are flying a non-ILS approach, always check the charts for notes like ‘VGSI and RNAV glidepath not coincident’.

For example, check out KMIA/Miami. It says what I just said above.

So what should you do?

Well, this depends on how not coincident they are, and also on what your operator says. Some say transition to visual and aim for the aiming point, others say ‘smoothly transition onto the VGSI’… it depends, and the main thing really is to be aware and to brief it!

Number 3: The Trouble with Long Legs

So far, we’ve discussed how there might be a slight different between where your ILS is bringing you versus where the PAPIs are (because of a slight positioning difference between the ILS antennae and the PAPIs themselves)

We’ve mentioned how they are not always that effective below around 200 feet, and we’ve looked at how other approaches might not be lined up at all with the PAPIs, requiring you to consider the visual transition before you get to it and go “huh?”

Let’s have a look now at the PAPIs themselves, because there is a little considered fact about them which United Airlines 129 were potentially reminded of the hard (lamp post) way…

The PAPIs are trying to achieve something a little more specific than just giving you some celebratory lights when you’re on the correct glide slope. They are actually set up to ensure that when you fly visually down the glide path, your dangly bits are kept clear of any obstacles.

The issue is – how far your dangly bits dangle (MWH), the difference between those and your eyeballs (EWH), and the height above the ground that your eyeballs sit at (MEHT), varies between aircraft.

To give you some figures, an A320 pilot sits roughly twenty feet above the main gear. An A350 or 787 pilot sits closer to forty feet. A Dash 8, a business jet, a Boeing 767 or an Airbus A380 are all different again. And while an A320’s gear extends down from the fuselage by around 3.6 – 4m, an A380’s hangs out a whopping 6m.

You get the picture.

PAPIs have to be calibrated to take into consideration the minimum wheel height (MWH), eye to wheel height (EWH), and your minimum eye height (MEHT) and these are not the same for all aircraft types which means the PAPIs are not optimised for all the types potentially using them.

Who wins?

Generally, the larger aircraft.

At airports regularly used by wide-body aircraft, the PAPI tends to be calibrated to their eye height because they are the most demanding aircraft from an obstacle-clearance perspective (they tend to have the most dangly footsies).

This means a narrow-body following two white and two reds all the way to the threshold may actually arrive slightly higher than intended. Not the biggest issue, and for sure better than the alternative. It is generally considered safer for an aircraft to be just a little high than just a little low, since ‘just a little low’ can actually be significantly low when over the threshold, and that can result in things hitting things.

So, designing for the larger aircraft provides the safest compromise.

A good example is LFMN/Nice, which has been calibrated for the A380 and so could you bring you in somewhat high if you aren’t in an A380. Or KEWR where runway 11/29 has been calibrated to a TCH of 60’

You can find this info in the ‘Additional Runway Information’ charts.

You can find your aircraft group type in various places. Here’s one the FAA made. For info, the Boeing 767 is a group 4 which has a threshold visual crossing height of 75’

*Quick fun fact: I used to fly the A340-600 into Bournemouth airport, which is not very long, while the A340-600 is very long. When we were landing they used to have to shut the airport at the end of the runway in case a truck went past, because we could have hit it.

So should we follow the PAPI?

Sure. Yes. Mostly.

On a visual approach, the PAPI is a great tool helping you set up and maintain a stable approach trajectory. It gives excellent trend information and an additional visual support, which can be compulsory for night time visual operations.

But if you are flying an approach, then they might not match up with the point the approach is aiming you down too, and if you aren’t in the aircraft group the PAPIs are calibrated for, then they might not be giving you the clearance you think they are.

Most of the time, you’ll never notice.

But there are airports where the MEHT is noticeably different, where the PAPI has been calibrated for larger aircraft, where terrain or obstacles influence the visual picture, or where local procedures specifically brief visual aiming points. This should hopefully be mentioned on a chart, or in your company airfield briefing.

Also, check for notes saying ‘Glidepath and VGSI not coincident’, and understand what that means.

With it in mind, brief how to handle it to avoid destabilising yourself by chasing the lights instead of maintaining a stable path and touchdown in the TDZ.

A final thought concerning ducks.

Not ducks, sorry, I mean ‘ducking’.

‘Ducking under’ is something I saw more often than I liked heading into EGLC/London City airport and EGHH/Bournemouth. Both airports, for the types I was flying in, had something in common – they are short runways (well, London City is arguably short for everyone, and has a viciously steep 5.5 degree approach).

Heading into a short runway can lead to pilots thinking a ‘short field’ landing is a good idea, and to achieve that they ‘duck under’ the glide – purposefully flying 1 white, 3 reds.

Why is this a problem? Well, hopefully fairly obviously (and if not have another read of the rest of the post) this means you’re lower than you are supposed to be and are doing away with some of your obstacle clearance. And while it might look fine to your little peepers up there at 50 or more feet, don’t forget your feet are still hanging out down below…

“Ducking under the glide” on an approach where the PAPIs are already calibrated for a smaller type will reduce your wheel clearance, potentially to an unsafe degree.

Another perspective

None of this suggests that the United crew were right or wrong. We don’t know all the facts, and accident investigations have a habit of uncovering details that aren’t obvious at initial review.

Either way though, it’s a good opportunity to remind ourselves that the PAPIs are a tool, and a very useful one, but only if we understand what it they are going to show us, what that means, and how to integrate it into our flight.