Where is Mode S required?

[dans2992]

Ignoring the upcoming ADS-B mandate, where are (or were) Mode S transponders required?

Was it based on aircraft type? Airspace?


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[John Collins]

Ignoring the upcoming ADS-B mandate, where are (or were) Mode S transponders required?

Was it based on aircraft type? Airspace?


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Part 91 operators - not required in the USA.

Part 135 may continue to use Mode A/C, but if replaced, it must be Mode S.

TCAS II is based on mode S.

 

[dans2992]

So, 121 operators are required to have TCAS, so mode S is required for them?


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[John Collins]

Yes is too short an answer, but it would be my answer if I didn't have to make it longer.

 

[flyingron]

TCAS II is based on mode S.

TCAS uses both mode S and mode C. It will listen for the mode S squits and will subseqeuntly interrogate nearby targets. It will also use mode S to coordinate a resolution with another TCAS aircraft. It also interrogates mode C transponders.

 

[flyingron]

So, 121 operators are required to have TCAS, so mode S is required for them?

If they have TCAS, they will have mode S. Not all part 121 aircraft must have TCAS II, but all 121 aircraft have mode S required.