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Old 21st November 2018, 22:54   #31
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Default Re: Pre-flight planning & checks for flying single-engine planes

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Originally Posted by AirbusCapt View Post
In a jet aircraft a good descent is idle thrust descent. It means, from the top of descent point, your engines are idling and the airplane is merely gliding down, until you establish on the ils with your landing gear down (say 6 miles to touchdown). A propeller airplane always needs power on descent, with the airspeed fixed.
Gliding down a jet airplane is not as difficult as it sounds, you practically do it everyday, however with no fuel, your options to go around or divert is zero, you are 100% committed to land at your chosen point.
The Flight Management Computer can calculate your idle descent. You need to have some good data on the wind direction and speed and various altitudes. Even then many FMCs still get it wrong. I have done endless simulations on idle descents on the 747-400 simulator, with huge variations in outcome.

When you study FMC bibles such as the FMC Users guide by FMC Guru’s Bill Bulfer and Skeet Gifford they are somewhat skeptical on the FMCs ability in this respect too. Maybe current versions are doing a better job.

More importantly, it is quite rare that ATC (can) allow(s) a continuous idle descent all the way from cruise altitude down to final. Certainly here in Europe and most of the USA it is probably quite rare. It is just an incredible busy airspace.

Whether you pull the throttle down to idle is usually determined by how fast you want or need to descent, or allowed to descent. ATC likes to see predictable behaviour!

I don’t think there is a fundamental difference between a huge by-pass engine idling away on a 777 or a propellor (variable or not) idling away on a Cessna.

In both cases you need to put the nose down to maintain a constant air speed. In both cases, whilst at idle power the fan / propellor actually acts as an air brake and creates additional drag. When you have an engine failure, the drag from either fan or propellor is considerably less! The difference is noticeable in how much more or less you need to push the nose down to maintain constant speed.

So I do believe there is not a difference on both jet or propellor planes between descending at idle power or with no engine power. Two very different things and both the 777 and the Cessna are capable of both.

Let me give you a very simple example when you use idle power setting to descent on a little Cessna.

So my home base was New Century airport which is only about 35 miles south of Kansas City International Airport. Whenever we arrived from the North it meant we had to fly through the B-airspace of Kansas City International. Not a big thing, even VFR you can ask for permission to transition through their airspace. But when it is busy they might not give you permission and divert you around the B-Airspace.

So if we knew it was busy we would just stay at cruising altitude fly straight over their B-Airspace (no permission needed, although we usually gave them a courtesy call so they knew what to expect, or we were on flight following and they already knew). At altitude as you probably know a B-airspace tends to be fairly large. So it extends far across Kansas City, even though the airport is 10 miles north of the centre.

So we just happily barrel along on cruising altitude with a good speed. Once we cleared the B-Airspace we cut the power to idle and spiral down to get ourselves in position for an approach to New Century.

Jeroen

Last edited by Jeroen : 21st November 2018 at 23:24.
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Old 21st November 2018, 23:13   #32
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Default Re: Pre-flight planning & checks for flying single-engine planes

Quote:
Originally Posted by Jeroen View Post
The Flight Management Computer can calculate your idle descent. You need to have some good data on the wind direction and speed and various altitudes. Even then many FMCs still get it wrong. I have done endless simulations on idle descents on the 747-400 simulator, with huge variations in outcome.

When you study FMC bibles such as the FMC Users guide by FMC Guruís Bill Bulfer and Skeet Gifford they are somewhat skeptical on the FMCs ability in this respect too. Maybe current versions are doing a better job.

More importantly, it is quite rare that ATC (can) allow(s) a continuous idle descent all the way from cruise altitude down to final. Certainly here in Europe and most of the USA it is probably quite rare. It is just an incredible busy airspace.

Whether you pull the throttle down to idle is usually determined by how fast you want or need to descent, or allowed to descent. ATC likes to see predictable behaviour!

I donít think there is a fundamental difference between a huge by-pass engine idling away on a 777 or a propellor (variable or not) idling away on a Cessna.

In both cases you need to put the nose down to maintain a constant air speed. In both cases, whilst at idle power the fan / propellor actually acts as an air brake and creates additional drag. When you have an engine failure, the drag from either fan or propellor is considerably less! The difference is noticeable in how much more or less you need to push the nose down to maintain constant speed.

So I do believe there is not a difference on both jet or propellor planes between descending at idle power or with no engine power.

Jeroen
I guess you don't fly for a living. With due respect to your thoughts, your thoughts on jet flying needs work.
In short I can try to clarify on a couple of things
Fmgc is a computer. It is garbage in garbage out. A poorly programmed one gives a poor outcome. Most of us don't rely on fmgc for our descent planning. Rather we plan our descent and program the box to follow our instructions. Descent planning is an important component of efficient flying and we take pride in making a fuel efficient, safe and comfortable descent, approach to landing.

Jet aircraft never fly with a nose down attitude. Even during descent on glidepath the nose is about 5 degree up. So pitching the nose down for descent doesn't happen. Descent is a function of ground speed versus rate of descent. You mantain attitude, adjust thrust for a required speed or rate of descent.

Atc got pretty little to do with efficient flight. You follow what they want, but you decide the best way to follow it. In regular practice, I can still manage long segments of idle thrust and some really low powered flight until descent, even in super busy places like Dubai, Hong Kong, Singapore, Mumbai etc.

You don't put your thrust levers to idle, you merely command a speed or rate of descent and the autothrust will command idle thrust from the engines.

Lastly, flying a simulation is not flying. A simulator is merely a tool to nail procedures and practice senarios.
Cheers and happy flying
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Old 21st November 2018, 23:43   #33
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Default Re: Pre-flight planning & checks for flying single-engine planes

Just to add to my previous post: The whole concept of an idle descent in an airliner is actually pretty complex. The notion of just closing the throttles and descending from 45.000 feet down to 2000 feet and finding yourself bang on the glide scope is not as easy as it sounds. It is in fact just one particular way of doing a so called VNAV descent. VNAV is a particular vertical flight path automated regime. So it determines how the aircraft descent or climbs by a combination of power settings, speed (restrictions) and control inputs.

Be aware, it gets really nerdy from here on. I just copied a few pages from my FMC user’s guide. FMC stands for Flight Management Computer. On most Boeing aircraft from a 737 to a 787 they will have 3 of these in the cockpit.

Everything to do with automated flying is entered here. As mentioned it can calculate at which point of the route you need to start you idle descent. I have taken a few pages that give some idea on how it does that. But also, what you as pilot need to enter and think through, because this box has certain limitations. Part of understanding and working with automation and computers is to have a very clear understanding how they will execute certain task and what they might not take into consideration.

This particular FMC guide is written and maintained by two pilots, both very experienced pilots. They thought that the manuals provided by Boeing, by Honeywell (the manufacturer) and their own airlines were not good enough. I can concur, I have the original FMC Honeywell manual. It is your typical American style FMC for dummies kind of book. The Boeing explanations aren’t all that much better. I have Cargolux and KLM manuals detailing the FMC. But nothing gets even remotely to this level of detail and understanding on how this box of tricks really works and should be operated!

Enjoy!

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Last edited by Jeroen : 21st November 2018 at 23:48.
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Old 22nd November 2018, 01:18   #34
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Default Re: Pre-flight planning & checks for flying single-engine planes

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Originally Posted by AirbusCapt View Post
I guess you don't fly for a living.
No, never claimed I did. Just a PPL/IFR, some endorsements. All expired by now, I might add. I do have an usual number of hours (for a non commercial pilot that is) on the 747-400 Full Motion SIM of CargoLux and Lufthansa. Used to drive over to Luxembourg and Frankfurt all the time when there was an available slot.

I also have close to about hundred jump seat rides under my belt in mostly various Boeings cockpits. Mostly in Europe, some in the USA. These days a little bit more difficult to get into the cockpit than before of course.

I take it you do fly for a living, good for you. Welcome to the forum. There are quite a few aviation enthusiast here and various thread on aviation. Hope you can share your knowledge, insights and experience with us.

Quote:
Originally Posted by AirbusCapt View Post
Descent planning is an important component of efficient flying and we take pride in making a fuel efficient, safe and comfortable descent, approach to landing.
I am sure you do. What I have seen from the jump seat is that ATC can and often intervenes with the best planning

Quote:
Originally Posted by AirbusCapt View Post
Jet aircraft never fly with a nose down attitude. Even during descent on glidepath the nose is about 5 degree up. So pitching the nose down for descent doesn't happen. Descent is a function of ground speed versus rate of descent. You mantain attitude, adjust thrust for a required speed or rate of descent.
True, did not want to make it any more complex than it already is. Nose down attitude is more relative than absolute in many cases and power settings control control speed/rate of descent on any plane. Large or small. But physically nose down is to some extend more the area of small planes.

Quote:
Originally Posted by AirbusCapt View Post
Atc got pretty little to do with efficient flight. You follow what they want, but you decide the best way to follow it. In regular practice, I can still manage long segments of idle thrust and some really low powered flight until descent, even in super busy places like Dubai, Hong Kong, Singapore, Mumbai etc.
As I mentioned before, from the jump seat I have seen that ATC can spoil the best plan.

Quote:
Originally Posted by AirbusCapt View Post
You don't put your thrust levers to idle, you merely command a speed or rate of descent and the autothrust will command idle thrust from the engines.
True, but for many understanding putting thrust levers to idle is easy to understand, whereas dialling in a speed setting into the MCP might not be so easy to follow. And on a Boeing at least, the throttles will subsequently be moved back by the auto throttle!

Of course, to the best of my knowledge there are no single engine airplanes with auto throttle. There was an article in Flying Magazine not to long ago. But even that article did not make it clear why not. Most glass cockpit in single engine planes do VNAV but with manual throttle control. (which makes for interesting situations if VNAV commands a pitch up or down and you are not following through. ).

Quote:
Originally Posted by AirbusCapt View Post
Lastly, flying a simulation is not flying. A simulator is merely a tool to nail procedures and practice senarios.
To me it is a little more. For me it is also an excellent way to try and understand how these machines are operated and how the technology works. At heart I am still an engineer.

Of course, these days certain simulator hours (on certain simulators) can and do count as flying hours in your logbook as well. Both on single engine plane as well as jets.

I posted my previous post before I noticed your post. I have quite a few manuals, but again, a bit dated, as I am not that active in Flying/Simulation/Aviation anymore. I still follow a few aviation forums, visit some aviation events and maintain to some extend my aviation network. (which gets me some free entrance tickets, the occasional ride etc)

Jeroen

Last edited by Jeroen : 22nd November 2018 at 01:27.
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