Simple explanation of Transponder 4 levels

There are 4 levels of transponders:
Level 1 transponders only have basic surveillance functions: they can identify UF0, UF4, UF5 and UF11 inquiries and reply accordingly. Transponders at this level do not have the ability to transmit data via data link.
Level 2 transponders, building upon Level 1, can also recognize UF16, UF20 and UF21 and can make corresponding replies. Most of the transponders are level 2. 
Level 3 transponders, an advancement from Level 2, can recognize UF24 inquiries but lack the ability to reply, which means they can’t send DF24 replies. 
Level 4 transponders, based on Level 3, possess the capability to send DF24 replies.

 

Regarding Mode-S inquiries,  there are 24 different types. The ones already defined are:
· UF=00 and UF=16 are utilized by TCAS systems.
· UF=04 and UF=05 are employed to inquire about aircraft altitude and identity.
· UF=20 and UF=21 represent Comm-A inquiries.
· UF=24 is designated as a Comm-C inquiry.
· UF=11 serves as an all-call inquiry.

 

Mode-S reply messages also exist in 24 different forms. The ones already defined are:
· DF=00 and DF=16 are used by TCAS systems.
· DF=04 and DF=05 are utilized for transmitting aircraft altitude and identity.
· DF=20 and DF=21 represent Comm-B replies, corresponding to Comm-A inquiries.
· DF=24 signifies a Comm-D reply.
· DF=11 serves as an all-call reply.
· DF=17~19 are dedicated to ADS-B broadcasts.

We're here to help you,

Not just sell products to you!

This website is intended exclusively for users outside of China.
The content herein does not constitute advertising activities targeting the Chinese market.