VS vs LVL CHNG
If you fly 737 CL in LVL CHNG mode, you just adjust MCP speed and the aircraft keeps with thrust closed just changing PITCH.
In VS, you have to watch the speed, because it is not protected by respective "pitch reduction" as it is in LVL CHNG. If you have XX rate of descent and AT closes levers, increasing of the VS will unevitably increase your speed and you will need to produce some drag or reduce VS again to keep speed it under Vmo/Mmo.
I used LVL CHNG often when I was starting my 737 flying, but then I found VS more controlable, more flexible for many situations, so it is my primary descent mode:-). If you choose VS for descent, rate is usually lower than in LVL CHNG - that means you start descent earlier and you have space to INCREASE the rate if requested by ATC. Level change is kind of "on the edge" no thrust, high speed - so significant increase of rate upon ATC request is not always possible without drag devices, which on the other hand reduce the pax comfort.
Last edited by Widewings; 12th Jan 2010 at 08:32.