FLCH
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NJA_Capt
Well-Known Member
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Could anyone explain the "FLCH" (Flight Level Change) Feature of a modern autopilot?
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Sure. It is basically a speed hold function. Ours engages as either IAS or mach. There are a lot of peculiarities with using this function, some like it some don't. The "deck angle" changes a great deal with the different wind speeds and what IAS you are at vs. what climb speed is set.
For example: If you are in cruise at 250 kts, and engage FLCH, which is set for a 200kt climb, the aircraft will pitch into a extreme climb rate which will quickly drop the speed to 200. Now you are out of excess thrust to continue climbing, so it pitches back down to near 0 rate of climb. It works much better to establish a "stabilized" climb and then engage the FLCH mode at the established climb speed.
Personally, I prefer VS down low and VNAV up high. I very rarely use FLCH.
Could anyone explain the "FLCH" (Flight Level Change) Feature of a modern autopilot?
[/ QUOTE ]
Sure. It is basically a speed hold function. Ours engages as either IAS or mach. There are a lot of peculiarities with using this function, some like it some don't. The "deck angle" changes a great deal with the different wind speeds and what IAS you are at vs. what climb speed is set.
For example: If you are in cruise at 250 kts, and engage FLCH, which is set for a 200kt climb, the aircraft will pitch into a extreme climb rate which will quickly drop the speed to 200. Now you are out of excess thrust to continue climbing, so it pitches back down to near 0 rate of climb. It works much better to establish a "stabilized" climb and then engage the FLCH mode at the established climb speed.
Personally, I prefer VS down low and VNAV up high. I very rarely use FLCH.
Looking4Lower
New Member
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Sure. It is basically a speed hold function. Ours engages as either IAS or mach.
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Yeah, it basically climbs/descends the plane according to a certain pre-programmed speed schedule. For example, in ours, using LVL CHG "high speed climb" mode will keep the plane in a 250-KT climb below 10,000...then it will increase the speed to 275 KT above that...then it will climb at .73 mach above 30,000' Of course, you must set the power yourself and that will determine the rate of climb.
Sure. It is basically a speed hold function. Ours engages as either IAS or mach.
[/ QUOTE ]
Yeah, it basically climbs/descends the plane according to a certain pre-programmed speed schedule. For example, in ours, using LVL CHG "high speed climb" mode will keep the plane in a 250-KT climb below 10,000...then it will increase the speed to 275 KT above that...then it will climb at .73 mach above 30,000' Of course, you must set the power yourself and that will determine the rate of climb.
DE727UPS
Well-Known Member
On the 757, FL CH will give you present speed, no matter if you are climbing or descending. Then, it will command the autothrottles/pitch to whatever setting necessary to complete the climb or descent in a 125 second period of time (don't ask me where that came from) and maintain the speed in the speed window.
Alchemy
Well-Known Member
In the ERJ, the FLCH button configures the flight guidance to present a pre-programmed "climb profile" or "descent profile" on the attitude indicator.
In the EMB-135/145/ER/LR, it will hold 240 knots until 10,000, then 270 until mach .56. In the EMB-145XR, it's 240 below 10,000 ft then 290 until mach .60.
Realistically .6 and .56 are too slow for ATC's liking, so we use VS above 10,000 ft to hold 290 knots until Mach .65.
On descent, the FLCH mode holds a 2000 fpm descent above 12,000 ft, then gradually decreases the sink rate to 1,000 fpm until 10,000 ft, at which point it holds 1,000 fpm the rest of the way down.
I find FLCH works best when you're using the flight director without the autopilot on. Otherwise you're better off using vertical speed, since the autopilot will pitch a bit erraticaly in order to maintain a constant speed.
FLCH usually only works well with the autopilot on days when the air is extremely smooth, at least on the climb.
On descents I usually use Vertical speed rather than FLC, just to be able to fine tune the rate of descent.
In the EMB-135/145/ER/LR, it will hold 240 knots until 10,000, then 270 until mach .56. In the EMB-145XR, it's 240 below 10,000 ft then 290 until mach .60.
Realistically .6 and .56 are too slow for ATC's liking, so we use VS above 10,000 ft to hold 290 knots until Mach .65.
On descent, the FLCH mode holds a 2000 fpm descent above 12,000 ft, then gradually decreases the sink rate to 1,000 fpm until 10,000 ft, at which point it holds 1,000 fpm the rest of the way down.
I find FLCH works best when you're using the flight director without the autopilot on. Otherwise you're better off using vertical speed, since the autopilot will pitch a bit erraticaly in order to maintain a constant speed.
FLCH usually only works well with the autopilot on days when the air is extremely smooth, at least on the climb.
On descents I usually use Vertical speed rather than FLC, just to be able to fine tune the rate of descent.
NJA_Capt
Well-Known Member
I agree with most everything you said, but have a question about the following quote.
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In the ERJ, the FLCH button configures the flight guidance to present a pre-programmed "climb profile" or "descent profile" on the attitude indicator.
[/ QUOTE ]
Are you sure about this? The CX and the ERJ share the same Primus AP (but could be using a different FMZ)...The VNAV button is the only one (for us) that uses programmed speeds, the FLCH button just locks the present IAS, whether it is IAS or M.
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Realistically .6 and .56 are too slow for ATC's liking
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For crying out loud, .56 is too slow for the traffic pattern!!!!
Sorry, you knew I had to throw that in somewhere. It's the only entertainment I get
[ QUOTE ]
In the ERJ, the FLCH button configures the flight guidance to present a pre-programmed "climb profile" or "descent profile" on the attitude indicator.
[/ QUOTE ]
Are you sure about this? The CX and the ERJ share the same Primus AP (but could be using a different FMZ)...The VNAV button is the only one (for us) that uses programmed speeds, the FLCH button just locks the present IAS, whether it is IAS or M.
[ QUOTE ]
Realistically .6 and .56 are too slow for ATC's liking
[/ QUOTE ]
For crying out loud, .56 is too slow for the traffic pattern!!!!
Sorry, you knew I had to throw that in somewhere. It's the only entertainment I get
B767Driver
New Member
In an FMS airplane VNAV is the most desirable pitch function for climbs and descents as it presents a speed/thrust/pitch profile to maximize economy. From a pilots standpoint, it is less user friendly than V/S or FLCH because many times a pilot will have to make 4 keystroke entries on the FMS just to enter a basic climb or descent.
Outside of VNAV, FLCH is nice because it will maintain a constant airspeed. V/S will not maintain a constant airspeed...for long climbs or descents V/S is a pain in the neck because it requires constant power manipulations to maintain the desired airspeed...and consequently poor fuel economy.
Most professional pilots will fly their airplanes maximizing fuel efficiency. When you fly with a pilot who does not it almost makes you cringe. Some techniques to save on gas are using VNAV, stay high as long as possible at cruise then make a power idle descent (TAS is higher at higher altitudes and fuel burn is less), select flaps at minimum maneuver speed as opposed to max flap placard speed, stay clean on the approach as long as ATC and speed permits.
Outside of VNAV, FLCH is nice because it will maintain a constant airspeed. V/S will not maintain a constant airspeed...for long climbs or descents V/S is a pain in the neck because it requires constant power manipulations to maintain the desired airspeed...and consequently poor fuel economy.
Most professional pilots will fly their airplanes maximizing fuel efficiency. When you fly with a pilot who does not it almost makes you cringe. Some techniques to save on gas are using VNAV, stay high as long as possible at cruise then make a power idle descent (TAS is higher at higher altitudes and fuel burn is less), select flaps at minimum maneuver speed as opposed to max flap placard speed, stay clean on the approach as long as ATC and speed permits.
NJA_Capt
Well-Known Member
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In an FMS airplane VNAV is ... less user friendly than V/S or FLCH because many times a pilot will have to make 4 keystroke entries
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All of our data is programmed prior to flight (unless you decide to change a speed), all we do is engage VNAV.
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...stay high as long as possible at cruise then make a power idle descent
[/ QUOTE ]This doesn't work so well outside of airline OPS. Everyone else is the redheaded stepchild (Even when we can outperform the daylight out of them). This year heading to AGS for the Masters tourney, we were fat, dumb and happy at FL430, when......"descend and maintain FL290" What is so strange about that?? WE WERE 400+ MILES FROM AGS!
They said it was for traffic management for ATL. We nor dispatch ever saw a NOTAM for an "event procedure" anywhere, and could have presented a serious fuel issue.
We run into these situations daily. ATC wastes more of my fuel than I could ever dream of.
In an FMS airplane VNAV is ... less user friendly than V/S or FLCH because many times a pilot will have to make 4 keystroke entries
[/ QUOTE ]
All of our data is programmed prior to flight (unless you decide to change a speed), all we do is engage VNAV.
[ QUOTE ]
...stay high as long as possible at cruise then make a power idle descent
[/ QUOTE ]This doesn't work so well outside of airline OPS. Everyone else is the redheaded stepchild (Even when we can outperform the daylight out of them). This year heading to AGS for the Masters tourney, we were fat, dumb and happy at FL430, when......"descend and maintain FL290" What is so strange about that?? WE WERE 400+ MILES FROM AGS!
We run into these situations daily. ATC wastes more of my fuel than I could ever dream of.
FlyChicaga
Vintage Restoration
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I agree with most everything you said, but have a question about the following quote.
[ QUOTE ]
In the ERJ, the FLCH button configures the flight guidance to present a pre-programmed "climb profile" or "descent profile" on the attitude indicator.
[/ QUOTE ]
Are you sure about this? The CX and the ERJ share the same Primus AP (but could be using a different FMZ)...The VNAV button is the only one (for us) that uses programmed speeds, the FLCH button just locks the present IAS, whether it is IAS or M.
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That's what it is. We have pre-programmed speeds for our FLC mode. We don't have VNAV. We do have a VNAV guidance for crossing restrictions and what not, just not VNAV AP flight guidance.
I agree with most everything you said, but have a question about the following quote.
[ QUOTE ]
In the ERJ, the FLCH button configures the flight guidance to present a pre-programmed "climb profile" or "descent profile" on the attitude indicator.
[/ QUOTE ]
Are you sure about this? The CX and the ERJ share the same Primus AP (but could be using a different FMZ)...The VNAV button is the only one (for us) that uses programmed speeds, the FLCH button just locks the present IAS, whether it is IAS or M.
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That's what it is. We have pre-programmed speeds for our FLC mode. We don't have VNAV. We do have a VNAV guidance for crossing restrictions and what not, just not VNAV AP flight guidance.
The CRJ doesn't even have a "level change" function. For vertical guidance we have Speed, Pitch, and Vertical Speed.
We also have the same advisory VNA that Matt talked about. It will tell you how fast to get down but not control the autopliot. You just set in the VSI it spits out and you will be where you need to be. Most people only use speed mode below 10,000. It starts to hunt for the correct pitch attitude after that by going through these oscillations....pretty annowing. So most people use vertical speed or pitch and adjust that using the "roller" knob to maintain the airspeed we want.
We climb at 250kts until 10,000. Then 290 kts to .74M (by the book), but realistically .7M works better.
We also have the same advisory VNA that Matt talked about. It will tell you how fast to get down but not control the autopliot. You just set in the VSI it spits out and you will be where you need to be. Most people only use speed mode below 10,000. It starts to hunt for the correct pitch attitude after that by going through these oscillations....pretty annowing. So most people use vertical speed or pitch and adjust that using the "roller" knob to maintain the airspeed we want.
We climb at 250kts until 10,000. Then 290 kts to .74M (by the book), but realistically .7M works better.
