What is the meaning of the letters h and i seen behind the relative altitude on the TCAS ND indication:

enter image description here

  • $\begingroup$ It is from the type-rating material. There isn’t any other information provided than the slide attached above. $\endgroup$
    – Anatolie
    Jul 27, 2022 at 20:35
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    $\begingroup$ It makes no sense. I've never seen n alpha character on that location on a TCAS display. As @757toga commented, the trend arrows are missing. On the map they should be to the right of the symbol. At the bottom, where the h and i are located. Perhaps in generating the presentation material someone got the wrong character set changing the arrows to the letters. $\endgroup$
    – Gerry
    Jul 28, 2022 at 0:25
  • $\begingroup$ The aircraft type is A320. $\endgroup$
    – Anatolie
    Jul 28, 2022 at 6:05

1 Answer 1


They mean the simulator or mockup is buggy and Wingdings 3 was missing / broken / not selected. There should be trend arrows there instead.

First smoking gun: this appears to be a photo of either a simulator or a mockup, as we can see from the Microsoft Windows mouse cursor:

enter image description here

Now, in many avionics software graphics engines - both for flight hardware and simulators (and of course for mockups) - it's common to use special fonts for symbology. In this case I'm guessing the "h" and "i" are meant to be rendered as trend arrows, using such a special font which has those symbols in place of normal letter glyphs.

Second smoking gun: check out Wingdings 3!

enter image description here

Character code 0x68 is "h" in normal fonts. 0x69 is "i" in normal fonts and a down arrow in Wingdings 3.

It should look more like this:

enter image description here

The trend arrows indicate that the target is climbing or descending.

  • 5
    $\begingroup$ Well done! Bounty on this answer as soon as the system will let me award it (24 hours, I think). $\endgroup$
    – Ralph J
    Jul 29, 2022 at 16:25
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    $\begingroup$ Thanks! I'm a software engineer (and pilot) and worked on professional flight simulators and avionics for 10 years so I had an advantage in spotting it. $\endgroup$
    – TypeIA
    Jul 29, 2022 at 16:32
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    $\begingroup$ Is there a way to crosspost this to StackOverflow? This is a fun confluence of computing and aviation bugs $\endgroup$
    – zymhan
    Jul 29, 2022 at 17:29

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