42 minutes ago, Stearmandriver said:

This may be a company selectable option as well, but in our aircraft it's definitely -15kts before Autothrottle wake up.  This is graphically depicted on the Max with a magenta speed band; the Autothrottles expect you to manage your speed within this band and will only wake up if you hit the edges of it.  In this shot you can see that the commanded speed is 279, AT in arm, and the bottom of the magenta band is 264, 15kts slow.  The NGs work the same way, they just don't have the magenta band.

Definitely a company option! Pretty cool that it’s different per company. Our band only goes to 5 knots below the target speed.

Some of our -900ers have this software on them as well.

12 hours ago, LRBS said:

No, that's not true.

I'll have to some research when I have a moment. I know it's rare but I definitely read that at least ONE commercial jet used to do this. Might have been 60s or 70s but it stuck in my head. ATC will allow minor deviation, I'm not talking about flying 35200 when assigned fl350 I'm talking 34850-35150 for instance with slow not abrubt coupling adjusting from autopilot. 

I'll either find the plane or the inaccurate source! 

So, the end result of my question is that the speed dropping 5 knots below that selected on the MCP before the autothrottle "kicks in" is perfectly normal?

Edited August 25, 2025Aug 25 by Christopher Low

1 hour ago, sloppysmusic said:

I'll have to some research when I have a moment. I know it's rare but I definitely read that at least ONE commercial jet used to do this. Might have been 60s or 70s but it stuck in my head. ATC will allow minor deviation, I'm not talking about flying 35200 when assigned fl350 I'm talking 34850-35150 for instance with slow not abrubt coupling adjusting from autopilot. 

I'll either find the plane or the inaccurate source! 

My former CFI was a line check pilot on the A320. and he told me that the Airbus do this, "soft cruise"- mode. Trade speed for altitude (max deviation of 50ft i think). But only at cruise, not in descents or any other flight regimes. But the effects are so gentle you hardly notice it unless you stare at the PFD like a fresh baked cadet. (his words)

1 hour ago, SAS443 said:

Trade speed for altitude (max deviation of 50ft i think). But only at cruise, not in descents or any other flight regimes. But the effects are so gentle you hardly notice it unless you stare at the PFD like a fresh baked cadet. (his words)

That is 100% correct. But not hundreds of feet, as was mentioned.

Absolutely.  All autopilot systems use an algorithm that fades in things like pitch rate, roll rate, or g... But you won't see more than about 50ft of deviation.

3 hours ago, Christopher Low said:

So, the end result of my question is that the speed dropping 5 knots below that selected on the MCP before the autothrottle "kicks in" is perfectly normal?

The end result is that it depends 😉.  It depends on phase of flight and auto throttle mode.  Basically, it's probably good enough.

10 hours ago, Christopher Low said:

So, the end result of my question is that the speed dropping 5 knots below that selected on the MCP before the autothrottle "kicks in" is perfectly normal?

Yes