737 EXCESIVE PITCH DOWN DURING DESCENT

[Guest mia]

Hi all!I have a question about the vertical speed on the 737-600/700 during the descent phase.ex: the aircraft is at FL350 and I want to start the descent pressing the FLCH option.the question is: Why the aircraft maintains an excesive pitch down during the initial descent?? (more than 12 degrees nose down) (about 4000 feet x min)How can I solve it?? Thanx in advanceSantiago

[basa 0]

Well, as far as I know, if you do that and you are maintaining the same sppeed you had in the cruise phase (say 320 knots or mach 0.80) when you press FLCH the aircraft will maintain that speed with idle power, so a high pitch down and vertical speed will be adopted.Solution: reduce selected speed for descent rotating the MCP speed knob to 280-270 knots .Jose Luis Basanta

[downscc 1,327]

Exactly, I usually select a mach number 0.02 less than my cruise and a verticle speed of about 3000 until below FL280. You can play with your speed setting to keep engines at or close to idle but maintain a smooth (passenger comfortable) descent.

[basa 0]

I think even 3000 fpm is a bit excessive descent speed.You will have to use too much spoiler to slow the aircraft when reaching 10000 ft.I use a max of 2500 fpm in the upper part of descent and a max of 1200-1500 in the lower part. It gives you a more easy speed control.Jose Luis Basanta

[downscc 1,327]

I (almost) never use spoiler. It (3000) certainly is too much below the mid-20's. Note I said I use 3000 until.... the much thinner air above the hi-20's needs a higher descent rate than lower unless you're in to cruise descents (which is what I do real world in a piston twin, keeps the jugs warm)... so you are right that 1200-1500 works. Most of the STARs that have stepped descents require less than 1000 fpm below 12000 (if they are stepped).