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tonymerry

Constant use of speedbrake required

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I mostly fly short haul flights i.e. typical Manchester to Heathrow. On this flight I will fly at 17,000 ft, which is around the real life altitude flown on this route. Starting the descent at the FMC TDC means a descent rate of some 1600 ft/min in order to get down to the landing altitude & this results in a speed that requires full speed brake nearly all the way down. Surely this is not realistic! Am I doing something wrong, or is this aircraft too slippery for it's own good? Any advice gratefully received.  TonyM

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Had you put wind information in the CDU on the DES Forecast page? Did you have a strong tailwind?

 

Dave

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Surely this is not realistic! Am I doing something wrong, or is this aircraft too slippery for it's own good? Any advice gratefully received.

 

Tony,

 

If I'm not mistaken, I'm pretty sure both tutorials reference how slippery the 737 is. If you haven't flown them, you really should. Doesn't matter if you've been flying since FS5.1 or only since yesterday.

 

The 737 in the real world is a very, very slippery aircraft (the 800, in particular). Descent planning - as Dave mentioned - is crucial. Certain STARs will also give you a lot of trouble simply in how they're constructed. In the United States, a lot of the STARs into the LA area are particularly tough.

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Check throttle settings, too.

 

 

Yep I would also check that the thrust levers are fully retarded during the descent as I have got an issue (not yet investigated on my side) with both T7 and NGX.

I have been surprised the first time having to extend the speedbrake all the way up to control the speed because if I don't retard my thrust levers at the beginning of the descent on my throttle quadrant, the thrust levers are only closed to 40% of thrust and not in the closed position in fsx.

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Winds, throttles or CI.  A high CI will set descent speed at or near VMO/MMO, which is at edge of operating envelop and more likely to need speed brakes.

 

I've not had this problem in the NGX since most my CI's are around 35-60 but in the B777 I'll run it around 200 and always change my descent speed from 314 (VMO) to 310 to avoid the problem.

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The 737 in the real world is a very, very slippery aircraft (the 800, in particular).

All modern airliners are very slippery. Airbuses too. The 777 is even more slippery. The difference is this isn't a default FSX 737-800 designed to be easy to use. So the old maxim applies, you can go down or slow down, but not at the same time. Add to that the notoriously ineffective 737 speedbrake. Unlike the default FSX speedbrake which is super-effective.

Starting the descent at the FMC TDC means a descent rate of some 1600 ft/min in order to get down to the landing altitude & this results in a speed that requires full speed brake nearly all the way down.

 

1600 ft/min shouldn't have required speedbrake. I rarely find I need to use it for any descent. It could be something to do with the flight condition you had at the time. What AP mode were you using? What weight and fuel load did you have? Was thrust at idle? Was there a strong tailwind that wasn't entered in the descent forecast?

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The 737 certainly is slippery and in early use I did find myself always having to use the speedbrake during parts of the VNAV descent.     One way I reduced the need for speedbrake was by adopting some 'policy' descent speeds.  Eg,  The FMC will often calculate some pretty high descent speeds (eg... 327 kts initially).    When you then hit a speed constraint, eg. 250kts, the aircraft finds it hard to decellerate (especially while still descending).   So I often manually enter a slower descent speed (280 kts works well), so that the aircraft will slow to this speed at the TOD, before it starts it's descent.

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Two things you can try:

 

1. When you see ARM on FMA press F1. This will make certain the throttles go to idle.

 

2. No matter what the winds actually are, I enter tailwind in the descent forecast for two or three altitudes.  Say the STAR that you are using heads to the northwest at 320 degrees and eventually turns north to 360 degrees. From 17000 ft. I would enter 15000 at 140/xx and 8000 ft. at 180/xx if 8000 is about where it turns to the north. The wind speed to enter comes with experience. Just don't overdue it.

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Thanks to all for your suggestions. I will try putting them into practice & report back. TonyM

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If you are using weather programs like ASN, addon airplanes do not like turbulence settings set too high. Cut back wind turbulence and all the others by 25-50%

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Hi All

Thanks again for all the suggestions. I have a much improved situation now. The main useful ideas are to check that the throttles are totally closing i.e. via F1, now getting N1 down to 33.9% (is that the right sort of figure ?). Also putting tail winds into the FMC helps. Now only occasional use of speed brakes required.

TonyM

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via F1, now getting N1 down to 33.9% (is that the right sort of figure ?).

For me pressing F1 will only work below FL300. So I usually press the key around FL295 and N1 goes to 40-41% decreasing as I lose altitude. 33.9% is in the ballpark with you starting down from 17000 ft.

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