What is the difference?And in which situations do you use LVL Change or SPD INTV

Edited February 25, 201214 yr by patrickbc

Spd Int is a mode of VNAV and will honor altitude crossing restrictions. Lvl Chg only looks at your Alt selector and down it goes. I use Spd Int for STARS or for turbulence speed and it can be used for NADP-2. On STARS, it's convenient to increase the descent speed/rate. Lvl Chg is good for vectors. It's also good for the Emergency Descent. I prefer Lvl Chg for single engine work, relying on it to keep my airspeed stable while I control the rate with the throttle.

Okay thanks. So you are mostly useing the SPD INV function?

Okay thanks. So you are mostly useing the SPD INV function?

I'd say I use SPD INT more en route and in the initial descent. I'm more likely to use LVL CHG when I'm on vectors and need to get down. If it's a vector and I'm low on profile, I'll use V/S.VNAV stays on the entire time if I'm doing RNAV approaches.What has caught some pilots is switching out of VNAV to LVL CHG and missing a crossing restriction. I think those pilots may mistakenly feel LVL CHG will give them better descent performance.

To be honest, Patrick, your best route here is to fully understand what each mode does. At that point, you'll be able to figure out why you'd use each, and from there you'll be able to figure out when you should use them.In brief:VNAV - operates in a pitch for speed mode, unless there are crossing restrictions (where it will operate with thrust for speed, pitch for climb)LVL CHG - purely pitch for speed (sets throttle to commanded Max N1 restriction - TO, CLB - and pitches to maintain the windowed speed)V/S - pitch for vertical speed, throttle for speedHow you apply them is the difference between a regular pilot and a good pilot. Take the plane up in the sim for a test of the modes to see how they behave.As Matt mentioned, LVL CHG is good for quick descents, but VNAV (+INT) will still offer you altitude protection for crossing restrictions.

Edited February 26, 201214 yr by scandinavian13