Slowing Down Slowly

[paulyg123 135]

OK (Thanks for the answers on the previous posts. I am getting ready to fly a LevelD NGX full motion simulator in 2 weeks and want to be as prepared as possible).I noticed (long ago) the 737 takes a long time to slow down. PDMG says it is a slippery aircarf - I agree.But I did some testing.At 5000' level with 15,000 lbs fuel 125,000 lbs ZF weight. It took 2 minutes and 2 secs to slow down from 250 kts to 200 kts. Then I started a 1200 fpm decent to 3000 ft and was at 260 kts at 3000 ft. This all was done with no flaps or speed brakes. Does this seem too excessive? I will verify these times on the full motion simulator - but what do you think? Oh one more thing. why is the mimimum N1 I can get 40%? With the throttles at idle I get 40% min, using F2 I can get 33% but it climbs to 40% quickly. Can this be my problem? Whatis the min N1 you get?

[Renzo 0]

The N1 thing you got, is basicly the EEC setting to correct idle setting. During flight, your N1 idle will be higher then on the ground. Also, next time you're on approach, reduce trust to idle (just hit F1, and it'll go down and back up to flight idle) and the lower the gear. You'll notice an increase in idle N1 in order that the aircraft doesn't slow down too much on idle with gear down. this is all done by the EEC in real life. (Electronic Engine Control, much like FADEC)

[Spin737 102]

At 5000' level with 15,000 lbs fuel 125,000 lbs ZF weight. It took 2 minutes and 2 secs to slow down from 250 kts to 200 kts.

RW, you can plan on slowing 10kts per mile. So it should be about 5nm. It took you about 7.5nm. That's 50% more. IMHO, it's becoming more and more clear that:

[MMartinov 48]

I have noticed that after gear down selected the idle trust raises with 5-10% (usually I am confirming that looking at the throttle quadrant in the VC - the throttles advance even though the A/C speed is way higher than the MCP setting).Same applies when descending from cruise flight level - the initial idle trust is actually not idle (all the way to the stoppers). This goes to about FL250 and then the throttles settle to the stops.This condition happens with A/T and manual control.My throttles are perfectly trimmed and 90% of the time I have no problem. Actually I learned to live with this fact and my approach speed is always under control. I've been thinking that the idle trust is varying depending on the flight conditions - e.g. descending from cruise altitude the engines must produce little more trust to keep up with the pressurization requirements.Can't figure why the thrust increases on gear down though... To keep up with the hydraulics?.. hardly...

[Renzo 0]

I have noticed that after gear down selected the idle trust raises with 5-10% (usually I am confirming that looking at the throttle quadrant in the VC - the throttles advance even though the A/C speed is way higher than the MCP setting).Same applies when descending from cruise flight level - the initial idle trust is actually not idle (all the way to the stoppers). This goes to about FL250 and then the throttles settle to the stops.This condition happens with A/T and manual control.My throttles are perfectly trimmed and 90% of the time I have no problem. Actually I learned to live with this fact and my approach speed is always under control. I've been thinking that the idle trust is varying depending on the flight conditions - e.g. descending from cruise altitude the engines must produce little more trust to keep up with the pressurization requirements.Can't figure why the thrust increases on gear down though... To keep up with the hydraulics?.. hardly...

If you would take a look to my reply, you would be much more wiser about this idle stuff.

[MMartinov 48]

Renzo that indeed is absolutely right. Higher Idle on the gauge should be fine on those ocasions.I have been wondering why the throttles move out of the idle detent though, if the A/T is disconnected and I have moved them to the back stop? Does the EEC still have authority over the throttles no matter what is my command? As well why the engine RPM goes up on the gear down?

[Renzo 0]

Renzo that indeed is absolutely right. Higher Idle on the gauge should be fine on those ocasions.I have been wondering why the throttles move out of the idle detent though, if the A/T is disconnected and I have moved them to the back stop? Does the EEC still have authority over the throttles no matter what is my command? As well why the engine RPM goes up on the gear down?

That is correct, the EEC still has authority over the idle position.As for the gear down, that is do compete for the extra drag given, so you don't suddenly get a smack in deceleration from the gears.