What IS speed intervention ?

[JSACKS 0]

How does SPD INTV work? I mean, maybe, why does it exist? If you have VNAV and also SPD/VS, and also LVL CHG, what is the purpose of SPD INTV? When would you typically use it?Thanks!Jonathan

[Guest JamieG]

In a nutsheel, Speed/Alt intervention is when you need to intervene in the VNAV (spd and/or alt) profile. (lol sorry couldnt resist). I'm sure you have noticed how the FMC calculates certain speed/alt restricitons/and expected crossings. However, I'm sure you've noticed with ATC--esp MS ATC that you will rarely be able to follow the FMC exactly. SPeeD/ALTitute INTerVention is used when ATC tells you to do something other than the FMC wants--without needidng to completely exit VANV.Sorry, I know that was confunsing and wordy. For example, if you are flying along and ATC tells you to slow to 250. You hit speed intv and dial in 250, and the plane will now slow to 250 but you can keep the VNAV profile.I believe that is how it works, but coorect me if i am wrong. I usually use ALT INTV b/c ATC usually never allows me to follow the profile.

[Tabs 2,790]

That is correct - you are overriding the optimal FMC calculated speeds/alts...