Is there a mod that allows planes to cruise at a certain altitude?

[Scientia1423]

Title says it all.

It would benefit me not having to keep my eyes on the altimeter incase the plane runs out of oxygen.

[G'th]

Theres Mechjeb, which offers an altitude and heading hold feature, not sure how it works.

Supposedly Persistant Rotation can offer a simpler if less intuitive option for this.

And then of course theres a couple autopilot mods out there, not sure if any of them work though.

[H3LK5]

I got sick of manually flying planes for hours on end, Atmosphere Autopilot works well and although the UI is a bit of a mess it's flexible and you can set it to keep a constant altitude while you continue to steer. 

[kerbiloid]

 

[SpaceMouse]

It isn't a conventional plane but the Heisenburg airship pack holds altitude through buoyancy.