A320 ALT* mode
 

Hello! What is engagement conditions of ALT* mode? FCOM, FCTM, AFM didn’t give me the answer.. I think there is time in seconds somewhere in documents or in airbus logic from engagement ALT* to ALT/ALTCRZ mode. And how airbus compute this? Any supposes? Thanks.

Hi,
ALT HOLD engages when the difference between target and current altitude becomes lower than 20ft. ALT* engagement is a function of v/s and difference of target - real altitude.

Simon

Depends on your update status, rate of climb/descend etc. First part is because now it enters ALT* earlier if there is traffic close to the level off altitude to prevent TCAS RAs.

Hi Surfaleks,

This is mentioned in the FCOM. Below is the extract from the FCOM - DSC-22_30-40-50-10
“ALT* engages, when ALT is armed, and the aircraft reaches the capture zone of the altitude target. ALT* engagement is inhibited during 3 s after the selected altitude is changed on the FCU.”

I need to calculate alt* by myself. I want to know how aircraft calculate this. What is the formula? It is a big difference between v/s 5000” and 500” for example..

ALT* is (loosely) based on a 0.15g demand to achieve the target altitude with some tuning in the very last part of the capture for smoothness. You can just use SUVAT equations to get what you need:

Δh=−v^2/2a

This gives you a blunt force tool to estimate your starting point, but you’ll need to use calculus to handle the final bit smoothly.

Maybe you mean 1,15g?)
And could you give explanation of this formula or make calculation for example when V/S is 700ft/min? Thanks!

Do you have any good reference for that? Incident report, or Airbus World would be welcome? I’ve been looking for hard info inside the box for how ALT* works for ages!