To Tabs or anyone else that cares to answer, what do the speed and altitude intervene buttons on the MCP do? All I could find was this "ALT & SPD INTV buttons for FMC hard speed and alt restraints". It also said they are an airline option. So what do they allow the pilot to do and when would they be used?Hiram Hunt

To Tabs...Hiram Hunt

His real name is Ryan Maziarz as you can read in his signature. I think it is more personal if you use this name

Speed intervention allows you to override the calculated FMC speed while in VNAV - when you push it the speed window digits become visible and you can adjust it with the knob.Altitude intervention is a bit more complicated - it has different functions depending on the context you push the button in:- While in a VNAV climb, pressing the button is going to remove the next altitude restriction in the flight plan that's lower than the set MCP altitude. This is really useful if ATC gives you a climb clearance that supersedes a restriction on the SID. Instead of mucking around with the LEGS page to delete the restriction, you just press ALT INTV.-If the airplane levels off and goes into VNAV ALT mode, selecting a higher altitude in the MCP and then pressing ALT INTV resumes the climb without any modifications to restrictions.- While in a VNAV cruise, pressing the button with the MCP altitude set higher than cruise altitude automatically sets the selected altitude as the new cruise altitude and initiates a cruise climb to it. If the MCP altitude is set lower than cruise, it initiates an early descent, the equivalent of the DES NOW prompt in the FMC.-While in a VNAV descent, pressing the button will remove the highest altitude restriction above the set MCP altitude - this is the same idea as the climb version, just in reverse for removing altitude restrictions.If you remove all the restrictions in a descent using the button, the plane will fall out of VNAV PTH mode and into SPD mode because it no longer has a valid end of descent (E/D) point with which to calculate a vertical path.

While in a VNAV cruise, pressing the button with the MCP altitude set higher than cruise altitude automatically sets the selected altitude as the new cruise altitude and initiates a cruise climb to it. If the MCP altitude is set lower than cruise, it initiates an early descent, the equivalent of the DES NOW prompt in the FMC.

That is going to be handy when in and out of various RVSM levels in Europe and elsewhere.

Wow! That sounds like a really handy button. So if you're in cruise and you set a new higher altitude and press ALT INV and the plane climbs to the new altitude does that now become the altitude set in the VNAV cruise page of the FMC? Does it recalculate the TOD automatically? And last question does the airplane return to VNAV mode when you reach the new altitude( Did it come out of VNAV mode when you initiated the climb?)? Thanks for the quick answer Tabs!Hiram Hunt

Ryan are you offended if I on occaision I have referred to you as Tabs in a post? I'm pretty sure I know the answer to this but I would like your response to be on record for Goof's benefit :-) LOLHiram Hunt

Wow! That sounds like a really handy button. So if you're in cruise and you set a new higher altitude and press ALT INV and the plane climbs to the new altitude does that now become the altitude set in the VNAV cruise page of the FMC? Does it recalculate the TOD automatically? And last question does the airplane return to VNAV mode when you reach the new altitude( Did it come out of VNAV mode when you initiated the climb?)? Thanks for the quick answer Tabs!Hiram Hunt

Yes, it sets the VNAV cruise page to the new altitude for you and recalculates T/D. The plane goes to VNAV SPD mode during the climb and back to PTH mode when it reaches the new cruise altitude.

Ryan are you offended if I on occaision I have referred to you as Tabs in a post? I'm pretty sure I know the answer to this but I would like your response to be on record for Goof's benefit :-) LOLHiram Hunt

No, I don't particularly care...

Sorry at this point ;DI just thought it sound a bit weird to be called Tabs (a few years ago i stopped playing the guitar so it always reminds me that i should start playing again lol)

I've seen pictures of a bunch of airlines that have the SPD INTV and ALT INTV deleted and blocked with little plates. Why would an airline not want to have this option other than cost? It seems like a convenient tool you could use on almost every leg.Hiram Hunt

Sorry at this point ;DI just thought it sound a bit weird to be called Tabs (a few years ago i stopped playing the guitar so it always reminds me that i should start playing again lol)

It's been my online handle for a long time - I've been making guitar tab books for like 10 years now, which is where it comes from, so not a big deal.

I've seen pictures of a bunch of airlines that have the SPD INTV and ALT INTV deleted and blocked with little plates. Why would an airline not want to have this option other than cost? It seems like a convenient tool you could use on almost every leg.Hiram Hunt

Pretty sure it is a cost thing yeah - you do have two pilots in the real airplane too so if you need to do one of these things you can have the PNF do it. You can also just use the manual MCP modes like LVL CHG or V/S to get the climb/descent started and then reprogram the FMC while the maneuver's already taking place. The manual MCP modes get used in real life a lot more frequently than a lot of simmers probably realize - it's often a lot easier in a busy terminal environment to just give it direct control like that vs. trying to reconfigure the FMC.

Can be confusing having a fmc calculated number on a MCP? My opinion