Definition
The worldwide network of interconnected voice telephone systems — landlines, mobile carriers, and the switching equipment that connects calls between them. In aviation, it refers to the ordinary phone network pilots use to reach Flight Service, clearance delivery, or other aviation services by dialing a published telephone number.
Plain English
The regular phone system. When a pilot picks up a phone and dials a number to reach Flight Service or another aviation office, the call travels over the PSTN.
Context Anchor
Seen in FAA acronym and notice references when a communication method is being identified as ordinary telephone service.
Derivation
‘Switched’ refers to the way phone calls are routed: the network ‘switches’ each call through whichever path connects the two phones. ‘Public’ means anyone with a phone can use it, as opposed to private internal systems. Knowing this helps the term feel concrete — it’s simply the everyday phone network everyone already uses.
Why Pilots Care
Many aviation services — Flight Service briefings, telephone clearance delivery at non-towered fields, TIBS recordings — are reached by ordinary phone call. Knowing PSTN just means ‘the regular phone system’ removes any mystery when it appears in FAA materials.
Intuition Check
Do not read PSTN as an aviation radio system. Here it means the normal public phone network used for regular telephone calls.
Example Sentence 1
Pilots at airports without a control tower often receive their IFR clearance over the PSTN by calling the published clearance delivery number.
Example Sentence 2
Older flight planning systems sometimes route updates over the PSTN when internet links are unavailable.