Description:

There's an issue with the way falling damage is calculated for Elytra that may cause the user to unintentionally die from softly touching surfaces, no matter the velocity of the user.

How is falling damage calculated without Elytra?

Source: https://minecraft.wiki/w/Damage#Fall_damage

"Fall damage is calculated based on distance fallen rather than on velocity when hitting the ground. The distance is accumulated based on a change in position each tick and rising does not reduce the accumulator, thus an entity bouncing in mid-air on the end of a lead accumulates fatal amounts of fall distance despite never being more than a few blocks above the ground."

How is falling damage calculated for Elytra?

Source: My own reverse engineering from debug info

Elytra flight fall damage calculated from your height since descent, and after landing. The 'height of descent' will be stored after descending at a >38.7 degree angle, and will be used to calculate the fall damage based on the Y level on landing.

The problem?

When the user is descending, and performing 'flipping maneuvers' to slow down the descend; their descending angle might not be below 38.8 degrees, causing the user to take the same falling damage as if the user aimed straight down during the full descend. The landing does not account for speed of the landing, giving unexpected results for the user.

This way of calculating falling damage for Elytra can very easily unintentionally kill the player; especially when the player is jumping from tall structures.

I recorded a few examples that go over the issues this behaviour might bring; and replicated the incident caused me to lose my hardcore world after jumping from an End City rooftop.

In this video you can notice that in both descending methods I took the same amount of falling damage with maxed out survival gear.
In the first part of the video it looks like I shouldn't be taking any damage, or not nearly as much as I did.
In the second part of the video I ignore any method to slow my descend and take the expected amount of falling damage (maybe less than expected).
From this test it is easy to conclude that Elytra wings falling damage is based on Y distance since the >38.7 degrees downwards descend, and does not factor in any velocity to reset this number. Meaning the user can very easily unintentionally die from this issue when jumping off tall structures like End City towers, or other tall structures if the user is not aware of this specific game mechanic calculation, or if they are not well equipped with protection enchantments to counter this unintuitive calculation.

Steps to replicate the issue:

1. Equip Elytra wings
2. Stand on a surface elevated high enough to jump from and fly (120 blocks)
3. Jump off the platform and activate Elytra Wings
4. Stare towards the ground at an approximate angle of 40 degrees down(F3) for the following steps
5. Flip your character around to slow down your 40 degrees descend
6. Touch the floor as gracefully as you can
7. Notice you took a lot of fall damage (likely dying in the process)

Additional info:

Throughout this issue I've referred to the 'descending angle'. This can be found by pressing F3 and looking at the vertical facing angle when in flight.

When your vertical facing angle is greater than 38.7, you will take fall damage on landing. When at 38.7 or lower; you are safe from any falling damage during Elytra flight.