Originally Posted by
Dont Hang Up
Transmitting Transponder system latency < 100 milliseconds (mainly the refresh rate of the altitude from the air data computer. The internal interrogation / reply processing of the Transponder will be small in comparison)
Radio propagation delay <1millisecond
Receiving TCAS system latency [the display works on a 1s refresh so that is the maximum latency]
So potentially the height data is maximum 1101milliseconds old.
At 5000ft per minute that's around 92ft as a maximum. But as an average probably much less.
This is simply for the display of course. The internal tracking algorithms of the TCAS unit are not constrained to the 1s refresh rate.
The climb rate is unknown to the flight crew other than that it is more than 500 fpm, so it is not possible to come up with a meaningful formula. You can use assumptions but as you say the result is probably much less than 100' which means that most of the time the difference between displayed altitude and actual altitude is less than the display precision.