Plain English Meaning

It's the call-sign style code that identifies one particular ILS approach. The 'I' tells you it's an ILS, and the rest of the letters identify which one. Pilots listen for it in Morse code on the localizer frequency to make sure they've tuned the right approach.

Full Definition

I-TOI is the ILS (Instrument Landing System) identifier for a specific runway approach, shown in figure 10-11 of the Instrument Flying Handbook as an example. ILS identifiers always begin with the letter 'I' followed by a two- or three-letter code, and are transmitted in Morse code by the localizer so pilots can confirm they have tuned the correct approach.

Context Anchor

Seen on instrument approach charts near the localizer frequency or approach information, including examples of timed approaches from a holding fix.