How Highlighting Works in the FAR/AIM App

The highlighting feature in the FAR/AIM app allows you to mark important regulatory and AIM text and have those highlights persist over time, even as the FAA publishes amendments, editorial revisions, and formatting changes.

Because FAR and AIM content is updated regularly, highlighting regulatory text is more complex than highlighting static documents. This article explains how the highlighting system works, why some text cannot be highlighted, and why alternative approaches are not appropriate for regulations and the AIM.

Why Highlighting Is Different for Regulations and the AIM

FAR and AIM content changes frequently. Amendments may insert or remove words, adjust punctuation, or reorganize paragraphs without changing the underlying meaning of the regulation.

If highlights were stored using fixed character positions or offsets, even a one-character change earlier in a regulation would shift the entire document and cause highlights to break or move to the wrong location. For this reason, the FAR/AIM app does not use position-based highlighting.

How Context-Based Highlighting Works

When you create a highlight, the app stores the selected text along with surrounding context. That context is later used to locate the same text after the regulation or AIM is updated.

As long as the highlighted text itself has not changed and can be uniquely identified within the document, the highlight will continue to appear in the correct location across updates. This approach allows highlights to persist through editorial revisions, reformatting, and minor wording changes elsewhere in the document.

This is the same general strategy used by modern web browsers for persistent text linking.

Why Some Text Cannot Be Highlighted

For a highlight to be reliable, the selected text and its surrounding context must uniquely identify a single location within the document.

In some regulations, this is not possible. Certain phrases, sentences, or even entire paragraphs appear multiple times with identical or nearly identical wording. When this happens, there is no reliable way to determine which occurrence a highlight should attach to after a future update.

Rather than risk attaching a highlight to the wrong regulatory text, the app disables highlighting in those cases. This behavior is intentional.

Example: Repeated Language in § 61.1

Some regulations contain identical language in multiple subsections. When this occurs, short selections cannot be uniquely identified.

For example, the following language appears verbatim more than once in § 61.1:

(A) Conducted in an appropriate aircraft
(B) That is at least a straight-line distance of more than 50 nautical miles from the original point of departure
(C) That involves the use of dead reckoning, pilotage, electronic navigation aids, radio aids, or other navigation systems.

Because this text appears in more than one location with the same structure and wording, it cannot be reliably highlighted on its own.

In these cases, selecting additional surrounding context can make the selection unique. For example, the following selection can be highlighted because it includes identifying context that appears only once:

ii) For the purpose of meeting the aeronautical experience requirements (except for a rotorcraft category rating), for a private pilot certificate (except for a powered parachute category rating), a commercial pilot certificate, or for the purpose of exercising recreational pilot privileges (except in a rotorcraft) under § 61.101(c), time acquired during a flight—

(A) Conducted in an appropriate aircraft;
(B) That includes a point of landing that was at least a straight-line distance of more than 50 nautical miles from the original point of departure; and
(C) That involves the use of dead reckoning, pilotage, electronic navigation aids, radio aids, or other navigation systems to navigate to the landing point.

Why Highlighting May Be Available Nearby but Not on a Specific Line

Highlighting availability can vary even within the same regulation. If a short phrase appears multiple times, it may not be uniquely identifiable by itself. Selecting more surrounding text often provides enough context to uniquely anchor the highlight.

This is why highlighting may be available in some locations but not others, even when the text appears similar.

Why Other Highlighting Approaches Are Not Used

Several alternative approaches were considered and rejected because they are not appropriate for regulatory material.

• Character-position highlighting breaks whenever text is inserted or removed, even for minor editorial changes.
• Page-based or layout-based highlighting fails because pagination and formatting vary by device, screen size, and app version.
• Allowing highlights in all cases and attempting to guess later risks attaching highlights to the wrong regulatory text.

The current approach prioritizes accuracy and persistence over allowing every possible selection to be highlighted.

Installation-Related Highlighting Issues

In some cases, highlighting may fail to appear where it normally should due to a local installation or state issue on the device. When this occurs, reinstalling the app resolves the issue by resetting the local data used for highlighting.

If reinstalling does not resolve the issue and the text does not appear multiple times within the same regulation or AIM section, support can investigate further.

Summary

The FAR/AIM highlighting system is designed to be durable, accurate, and safe across regulatory updates. Some text cannot be highlighted because it appears multiple times with identical wording, making it impossible to anchor reliably.

When a highlight does appear, it is because the app can confidently ensure that it will continue to point to the correct regulatory text over time.