Originally Posted by
tartare
Forgive my light plane flying ignorance.
If, in any large passenger jet, the power levers are manually advanced to full power - i.e. firewalled, you will get full power regardless of auto-throttle or autopilot settings, right?
In other words, manual advance of the power levers will over-ride all automatics?
To add a bit to 172's answer, on any Boeing or MacDac, commanded thrust is dependent on the thrust lever position. Period. So if you push the throttles forward, you'll get more thrust.
However things are not always that simple - as 172 points out, if the autothrottle is active it may start pulling the throttles back (although on some installations a large manual override of the A/T will cause it to disconnect). Further, with wing mounted engines you're going to get a significant pitch-up moment from the increasing engine thrust (FBW will largely hide that, although it's still there - and if FBW is in a degraded mode for some reason you can get a big surprise)(not an issue with the MD-80 series tall mounted engines).
From an engine guy's perspective, simply firewalling the the levers can create another issue - pre-FADEC (or FADEC operating in degraded mode) - you can get a
big engine overboost. Not only is this really hard on the engines (and has been known to cause engine failure), the pitch-up moment with wing mounted engines will be
much larger - potentially enough to make aircraft control difficult.
If memory serves, the MD-80 engines are pre-FADEC, which may have influenced the crew's actions with regard to manually advancing the throttles.