PAPI guidance mislead when using external view

[MissTschai]

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Brief description of the issue:

I noticed today that the PAPI lights guidance is not based on the aircraft height but the current viewpoint. This means that if you are in external view mode the papi lights change depending on the angle you look at the aircraft and how far you are zoomed out. This can’t be the desired behavior.

Provide Screenshot(s)/video(s) of the issue encountered:

With active pause and then changing external view position:

high: 4w

close to aircraft: 2w

below: 0w

Detailed steps to reproduce the issue encountered:

I flew into EDLW ILS 24 but probably same elsewhere.

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Do you have the same issue if you follow the OP’s steps to reproduce it?

Provide extra information to complete the original description of the issue:

If relevant, provide additional screenshots/video:

[DorchFlyer]

Perhaps it is just me, but this is the behaviour I would expect. The papi lights change according to the angle you view them from. If you are above the aircraft they indicate you are viewing from higher up and vice versa.

[MissTschai]

Interesting, I would expect that they are tracking the height of the plane.

[Vibstronium]

The lights are set up at a fixed angle; they don’t actively track anything. You see red or white depending on the angle to your eye or camera’s physical viewpoint in 3d space.

The simulation is behaving correctly here (though there are other problems with placement of lights from what I hear).

[F737NG]

@MissTschai

I noticed today that the PAPI lights guidance is not based on the aircraft height but the current viewpoint. This means that if you are in external view mode the papi lights change depending on the angle you look at the aircraft and how far you are zoomed out.

That’s exactly the desired behaviour.

Don’t think of the PAPI as guidance based on “aircraft height”, rather the desired approach angle.

For instance, the 747 has a much higher flightdeck than most airliners.
If it’s on an ILS approach, the flightcrew would see three whites and one red on the PAPI when descending the glideslope per the ILS beam.

See in the video below how this 747 is on profile, yet the PAPI shows exactly what I describe:

https://www.youtube-nocookie.com/embed/8-vOExi_X0I

This is why the three-bar VASI exists:

It’s all just geometry.

[N6722C]

@DorchFlyer

Perhaps it is just me, but this is the behaviour I would expect. The papi lights change according to the angle you view them from. If you are above the aircraft they indicate you are viewing from higher up and vice versa.

+1 seems 100% correct to me, and while it makes geometrical sense, I must admit, I have never tried viewing a PAPI from such extreme external views in RL

[MissTschai]

Brilliant, thanks guys for the detailed and informative responses.

[MissTschai]

Hilarious

[CharlieFox00]

Lots of great explanations in here! I have nothing to add, except a pic of an installation in which you can see the difference between the red and white sectors, and maybe discern the different angles of each light unit.

Well…

@Vibstronium

The simulation is behaving correctly here (though there are other problems with placement of lights from what I hear).

This is my pet topic, haha. Yes, many are the wrong type and many are sited incorrectly on smaller runways.