Definition
A modification to the standard pressure altimeter that allows it to electronically transmit the aircraft's pressure altitude to a transponder, which then sends that altitude information to air traffic control radar. The encoding altimeter converts the mechanical altitude reading into a digital signal referenced to a fixed pressure of 29.92 inches of mercury, regardless of the altimeter setting shown in the Kollsman window.
Plain English
An altimeter that can send the aircraft's altitude electronically to ATC through the transponder, so controllers see the aircraft's altitude on their radar screen.
Context Anchor
Seen in instrument flying when learning how altitude information is displayed in the cockpit and reported electronically through the transponder.
Derivation
Encoding comes from 'code' -- to convert information into a form (here, a digital signal) that another system can read. The altimeter's mechanical reading is encoded into electronic data the transponder can transmit.
Why Pilots Care
Gives ATC an accurate, continuous picture of your altitude for traffic separation and terrain clearance.
Grounding Statement
The key idea is that encoding does not just show altitude to the pilot; it packages altitude information so it can be sent electronically.
Intuition Check
Do not assume “enhancement” means the altimeter is simply more accurate. Here, the important enhancement is that altitude information can be encoded and transmitted to other equipment.
Example Sentence 1
Before departing into Class B airspace, the pilot confirmed the encoding altimeter and transponder were working so ATC would receive accurate altitude readouts.
Example Sentence 2
In the climb the controller used the data from the altimeter enhancements to keep traffic separated from our flight path.