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vladohd

PMDG 737 speed brake, aircraft is not slowing down.

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I have a problem with slowing down the 737 during the approach. I can see the FMC message " drag required " when I set the speed brake, I can see in the cockpit that the lever is fully deployed, and on the wings, the speed brakes are up, so everything seems to be ok, but it has absolutely no impact on speed. The aircraft is not slowing down, the descent rate is not increasing, and the engines are not increasing power. Nothing is happening just the animation. I also tried to deploy speed brakes during the cruise, animations are ok, but no impact on speed, or on engines. is it some knowing bug? or am I missing something? Any tips?

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Just a thought do you have another key binding to the speed brake ? might want to check


Rich Sennett

               

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Perhaps some additional information like altitude, speed, FMA readings, N1, etc., might help.

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The speedbrakes on the NG are not effective.  It's been said many times over that you can't rely on them to do much slowing. You could be descending at 2000 feet per minute and actually gain speed with them deployed and engines idle.  I don't know the actual numbers, but I imagine someone could give you better example of what you should expect to see.  I have accidentally left them deployed on approach and didn't even know it.

 

In the real world, accommodations are often made knowing that modern jets are much harder to slow.  The 3:1 glide ratio is more like 4:1.  ATC would typically give you appropriate altitudes and speeds you can actually meet.  Some STARs are not very friendly about helping you slow down and meet the altitudes to get configured on final.  I noticed the other day that the JANNY5 arrival into KBUR was the best one I've seen so far.  It was essentially a 1000 foot per minute descent all the way.

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Orlaam is absolute right.

There are real world pilots that stated this clearly. 737NG is very hard to slow down.

Most effective is to drop gear and increase flaps, but you have to be at low enough airspeed to not overspeed.

Some STARS are tough and you need to really pay attention, maybe even deploy speed brakes before more drag is called for.

The spoilers or brakes are good at spoiling lift once touched down, but not very effective as speed reduction devices.

Keep a close eye on the descent profile, and as soon as you start to deviate high, do something. Like take over from VNAV. Or if really bad do a turn around a holding pattern, some approaches require a turn around a hold as part of the approach. Such as ILS 29 into KPWM with ENE as via.

Edited by 177B
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1 hour ago, vladohd said:

I have a problem with slowing down the 737 during the approach. I can see the FMC message " drag required " when I set the speed brake, I can see in the cockpit that the lever is fully deployed, and on the wings, the speed brakes are up, so everything seems to be ok, but it has absolutely no impact on speed. The aircraft is not slowing down, the descent rate is not increasing, and the engines are not increasing power. Nothing is happening just the animation. I also tried to deploy speed brakes during the cruise, animations are ok, but no impact on speed, or on engines. is it some knowing bug? or am I missing something? Any tips?

It has been said by wise old 737 driver that with a 737 you do not descend and slow down.  You can do one or the other but not both at the same time.

Ditto to what the others said, about the effectiveness of the speed brakes.

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Lower the gear next time. It will introduce a lot more drag than the speed brakes.

The common saying, as Rhett said above, is "You can descend or slow down, but not both." But the gear should help you not gain-speed.

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Another item I've heard mentioned by Boeing drivers: Above 250 knots the speed brake is more affectual than below 250 knots.

Here's another speed brake note: With the Airbus, the speed brake will only deploy 1/2 of full extent with the autopilot on.

Another one: The speed brake on the BEA 146 looks funny.


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Yes to all the above comments, but the speed brakes do actually meet expectations so long as those expectations are reasonable. If you wait for the DRAG REQUIRED message on the CDU, you're likely to bust either a speed or altitude restriction. From my reading of various websites, it appears that the VNAV descent function slowly gained reliability as the FMC versions were updated over the last 15 years or so. RNAV STARs need to be carefully monitored and the aircraft's energy status managed with a combination of throttle, pitch, and spoiler deployment.

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7 hours ago, jrw4 said:

Yes to all the above comments, but the speed brakes do actually meet expectations so long as those expectations are reasonable. If you wait for the DRAG REQUIRED message on the CDU, you're likely to bust either a speed or altitude restriction. From my reading of various websites, it appears that the VNAV descent function slowly gained reliability as the FMC versions were updated over the last 15 years or so. RNAV STARs need to be carefully monitored and the aircraft's energy status managed with a combination of throttle, pitch, and spoiler deployment.

In addition to the comments above

I would highly recommend  doing some  forward planning. If you are expecting a STAR with a lot of "at or above" altitude restrictions. Carefully set the most critical ones to a firm number by removing the A from the altitude restriction so that the aircraft doesn't find itself having to meet drastic descent profiles in critical phases where energy management is important. Got to be ahead of the AC or you will be chasing stuff all the way  down and that's the last thing you want.

With the removal of some ambiguity on the vnav waypoints i find myself not needing to reach for the speedbrakes that much anymore if at all.

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12 hours ago, vladohd said:

I have a problem with slowing down the 737 during the approach. I can see the FMC message " drag required " when I set the speed brake, I can see in the cockpit that the lever is fully deployed, and on the wings, the speed brakes are up, so everything seems to be ok, but it has absolutely no impact on speed. The aircraft is not slowing down, the descent rate is not increasing, and the engines are not increasing power. Nothing is happening just the animation. I also tried to deploy speed brakes during the cruise, animations are ok, but no impact on speed, or on engines. is it some knowing bug? or am I missing something? Any tips?

A RL 737 pilot said that the best way to deal with that is to make a steeper descend than required as to level off in time to loose that speed again. But, as mentioned, prepare the descent and manage your speed prior to the descend.


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10 hours ago, RichieFly said:

Here's another speed brake note: With the Airbus, the speed brake will only deploy 1/2 of full extent with the autopilot on.

Only half true. That goes for the A320. But ONLY the A320. Not for the A319 or A321.

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As others have noted, it has always been the case that the 737, going right back to its 100 and 200 series, is a slippery aeroplane which is difficult to slow down when descending, which is why it's always been the case that 737 pilots occasionally use the landing gear as an unofficial speed brake.

However, if you're still a bit hot and high on approach, there are two things you can try; one is to sideslip it to lose some speed and height, the other is to do what you should always be prepared to do with any aeroplane apart from a glider, and that's go around.

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Be in front of your airplane and you'll be fine.

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49 minutes ago, Chock said:

As others have noted, it has always been the case that the 737, going right back to its 100 and 200 series, is a slippery aeroplane which is difficult to slow down when descending, which is why it's always been the case that 737 pilots occasionally use the landing gear as an unofficial speed brake.

However, if you're still a bit hot and high on approach, there are two things you can try; one is to sideslip it to lose some speed and height, the other is to do what you should always be prepared to do with any aeroplane apart from a glider, and that's go around.

You absolutely do not cross control a jet airliner into a sideslip to lose height/speed, at least not in real life.

Speedbrakes are OK on the 737, but they work much better at high speeds as drag is proportional to the square of the speed. 

You absolutely can 'go down and slow down,' we do it all the time. The reduction in total energy state does not change, but being low and a bit fast is slightly easier to remedy than being high, so we often choose to go down before we slow down. 

I don't own the PMDG 737 so can't comment on the specifics of the sim.

Edited by 2reds2whites
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