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keeping below 250 kts

crosscheck9 Guest

The other day, I was flying in an a340-311 Lufthansa by Posky, and I was approaching Frankfurt/Main airport. At about 11000ft, and descending, I began trying to slow down to about 245 knots, fot transition below 10,000, but it wouldn't get down quick enough, so I opened spoilers, and it did the job, but all through the approach, I had to keep deploying spoilers to remain below 250 kts. Is there another way around this, besides extending flaps.

Pro Member Chief Captain
Matthew Shope (mypilot) Chief Captain

Bring your throttles down to idle about when you cross FL180. I have the same problem in the 747.

crosscheck9 Guest

In the a340, I had my throttles at idle since about FL240, and descending. I needed that kind of rate of descent in order to get down to my requested altitude fast enough. So I had no room to lower the thrust anymore.

Pro Member First Officer
rob (Habu) First Officer

Start your descent sooner, then bring throttles down while still in level flight to slow down before descent. Air brakes must be used during descent. When you fly for real next time, get a wing seat and watch the air brakes (spoilers). rob

Pro Member Captain
John Hodges (originalgrunge) Captain

It's not necessarily true that the speedbrakes are used on all flights, and if possible it's generally discouraged (bad on fuel performance). However, they are there for a very good reason =), and I too have been on a few flights where they are used very liberally.

Try flying using real world STARs, (www.myairplane.com) those are designed as published to guide you down nearly perfectly from T.O.D. down to final on approach, without needing to do much diving to make the next altitude. The flight sim is really poor at giving good descent information.

I went from descending with speedbrakes full open on descent (usually around 2200-2400fpm minimum descents) with the default ATC to descending at a graceful 1000fpm (+ or - 300 fpm) when I fly the published routes and plan my own descents (or have my FMC do it for me Wink. I usually only need to use the speedbrake when I've got a quick change in speed to make (like for the turn to final) or something of the sort.

Guest

Sounds like your attitude is far too nose-down and you probably need to begin the speed reduction and descent much earlier. You do not have to have the nose pointed towards the ground to descend. The flare for landing proves that point.

Your initial airspeed at the higher altitude needs to be reduced below 250kts to allow for the increase you are going to get when you drop the nose to make the required rate of descent.

For any given configuration of power and attitude an aircraft will return a given performance. For example. If you have power at idle and a 15 degree nose-down attitude, the airspeed and rate of descent will eventually stabilize and will remain at that airspeed and rate of descent until you do something to change the configuration.

What you need to know is how much the airspeed will increase for the configuration you are flying in the descent and reduce your airspeed at the higher altitude by that much before starting the descent.

The other way to look at it is, what configuration of power and attitude do I need to have to descend at a given airspeed and rate of descent? There are top and bottom limits for safety and comfort and these limits determine the minimum distance from the destination that you can start a safe and controlled descent; unless you want to fly a descending spiral but that is not a realistic option from a fuel economy stand point. Probably will upset ATC too.

After you have reduced power to idle, hold the nose up until the airspeed bleeds off. Give the aircraft time to respond. By the very nature of their streamlined design, the jets take a good while to slow down. As the airspeed drops you will begin to descend because the aircraft can't maintain altitude with no power and a level or nose high attitude.

Don't use flaps to control speed. They are deployed after you reach the required airspeed not the other way around.

crosscheck9 Guest

Thank you all for your replies.

You do not have to have the nose pointed towards the ground to descend

Guest - When descending with that a340, the nose wasn't pointed to the ground. I was ranging from 0-2 degrees pitch. I understand that it is improper to descend with a pitch down attitude, and so I never do it. However, many of you also told me to begin my descent earlier. How can I do that? ATC will only give me clearence to descend at a certain distance away from the airport. Also, I don't understand how real world pilots would begin there descent earlier. I mean, they generally say they need about 20 minutes to land from the beginning of the descent, so if you descend farther away, at a rate of about 1000fpm, (as stated by originalgrunge) it'll probably take about 45 minutes to land. Can someone please post a link that describes STARS in detail? Again, thank you all for your help. If I can get a little more clarification, I would be most grateful. Have a good day/evening. 😀

Guest

There's nothing wrong with a nose down attitude but a lot of sim flyers don't always appreciate it is possible to descend with a nose high attitude.

As part of the flight plan you can request a specific cruise altitude for any leg of the flight and request a change because of weather conditions etc. If flying a STAR, the waypoints will have associated height and speed requirements.

Unfortunately, as far as I am aware, the FS Flight Planner doesn't allow altitude and speed to be set for individual waypoints. You need an add on something like FSNav for that.

You can also request an altitude change at any time with ATC. (I think FS allows that). What FS ATC is doing is leaving it to the last minute to bring you down, if you haven't started already, and generally it is too late. If you do the simple calculation and make the request to descend before FS ATC tells you, then it will work with that - use the old 4 x altitude change to convert to distance required to make the descent.

eg: (Let's say ground speed is the same as airspeed to keep it simple) To step down 10,000' with an airspeed of 250kts at 1000' fpm is going to take 10 minutes or approx 42 miles.

Extending that example to make a single, continuous descent (let's say the airport is at sea level) from your 40,000' is going to take at least 40 minutes or approx 168 miles.

Real world will step down through various altitudes on the way to landing, so from 40,000 it is not unususal to have the initial descent start an hour before landing. If you're not looking out the window or watching the flight map if there is one, other than a change in engine sound, you will probably not notice it. What you hear on the PA about 20 minutes from landing is the pilot announcing he is starting his final descent and approach. It's also a clue for the cabin crew to start the final prep for landing.

From the economic point of view, the longer the aircraft stays high the more fuel it requires to keep it at altitude so making a gradual, power off descent (in effect an assisted glide) saves fuel. It also avoids making a steep descent and having the passengers, that have just eaten breakfast, re-decorate the inside of the cabin for free. 😂

crosscheck9 Guest

Thanks alot for that post Guest. It really helped me out. I guess it's not unusual that a pilot begins the descent so far away. Again thank you all.

Pro Member First Officer
Jason (Av8r77) First Officer

Actually, you don't use more fuel at higher altitude.

As an aircraft climbs into the less dense air the parasite drag decreases, but the induced drag increases. For a jet range is significantly affected by altitude. As the aircraft climbs higher the max SR (V/FF) keeps getting better and better. Therefore, the jet aircraft should always be operated at high altitude unless there is a very strong headwind.

The Jet Engine converts fuel to thrust. Since the air is less dense, and usually cooler, the higher you go there is less fuel needed to produce that thrust to attain a desired groundspeed. A headwind will obvisouly affect this fact.

Guest

Of course, that's why jets fly high.

But, I bet it takes more fuel to stay high for longer and have a steep descent than it takes to have a long descent with engines on low output.

Pro Member First Officer
Jason (Av8r77) First Officer

Most aircraft will perform stepdowns. You want to be about 5-7k within 40 miles of the airport (if terrain allows). This way you can still get NAVAIDS and set up for an approach into your field.

ATC will have areas in their control that they put all aircraft through at a gien altitude. STARS are something entirely different, and most times ATC will ammend your arrival with vectors and altitudes of some sort. All STARS really do is set up a route that everyone comes in on for safety and organization.

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