Descent Planning
04-02-2012, 11:50 PM
#22
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Joined APC: Jul 2005
Posts: 248
For 3 degree descent, 5 x GS is a good approximation. The formula is derived from Tan (3°) = V/S ÷ GS.
Tan (3°) = .0524
.0524 = V/S ÷ GS ⇒ (.0524)GS = V/S
GS units are nm/hr, need to convert to fpm.
(.0524)GS nm/hr x hr/60min x 6000 ft/nm = (.0524)(100)GS = V/S
5.24 x GS = V/S(fpm) to be precise.
Tan (3°) = .0524
.0524 = V/S ÷ GS ⇒ (.0524)GS = V/S
GS units are nm/hr, need to convert to fpm.
(.0524)GS nm/hr x hr/60min x 6000 ft/nm = (.0524)(100)GS = V/S
5.24 x GS = V/S(fpm) to be precise.
04-04-2012, 04:47 AM
#24
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Joined APC: Jun 2007
Position: Legacy FO
Posts: 4,096
Originally Posted by dojetdriver
And remember everyone, the pu$$y paddles are for your mistakes, NOT the controllers.
04-04-2012, 09:03 AM
#25
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Joined APC: Aug 2011
Posts: 1,134
Originally Posted by KC10 FATboy
Stupid comment. Anyone listening to this comment and not using the brakes because of passenger comfort, large egos, or any other reason shouldn't be PICs.
But it's usually phrased as follows;
Controller: "what do you mean unable on the crossing restriction I just gave you, don't you have speed brakes on those planes"?
Pilot: "don't give us a restriction so late that it's impossible to make it. The speed brakes are for our screw ups, NOT yours".
Google it.
06-17-2012, 04:13 AM
#26
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Joined APC: May 2006
Position: ATP, CFI etc.
Posts: 6,056
angle of descent
I was watching an aviation video where the pilot figured out his descent angle in order to make a fix and tell his autopilot what angle to use. Most people just use a descent rate in feet per minute. I never read of any easy way to do an angle calculation without a calculator, but this guy did it on his kneeboard real quick, and it was supposedly a real enactment, so I thought about it a little while, and came up with this fairly simple formula. Easy enough but still requires pen and paper.
>Divide the altitude to be lost by the distance in ft, and then divide by 1.7, and slide the decimal.
Ex. 5000 ft / 10 miles (61000 ft) = .082 / (1.7) = .0487° --> 4.8°
Anybody know one that does not require pen and paper?
>Divide the altitude to be lost by the distance in ft, and then divide by 1.7, and slide the decimal.
Ex. 5000 ft / 10 miles (61000 ft) = .082 / (1.7) = .0487° --> 4.8°
Anybody know one that does not require pen and paper?
06-18-2012, 07:26 PM
#27
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Joined APC: Sep 2007
Position: CA
Posts: 141
Originally Posted by Cubdriver
I was watching an aviation video where the pilot figured out his descent angle in order to make a fix and tell his autopilot what angle to use. Most people just use a descent rate in feet per minute. I never read of any easy way to do an angle calculation without a calculator, but this guy did it on his kneeboard real quick, and it was supposedly a real enactment, so I thought about it a little while, and came up with this fairly simple formula. Easy enough but still requires pen and paper.
>Divide the altitude to be lost by the distance in ft, and then divide by 1.7, and slide the decimal.
Ex. 5000 ft / 10 miles (61000 ft) = .082 / (1.7) = .0487° --> 4.8°
Anybody know one that does not require pen and paper?
>Divide the altitude to be lost by the distance in ft, and then divide by 1.7, and slide the decimal.
Ex. 5000 ft / 10 miles (61000 ft) = .082 / (1.7) = .0487° --> 4.8°
Anybody know one that does not require pen and paper?
I never bother calculating my flight path angle. What is important to me is the descent rate required to meet the restriction. If i have to descend 5000ft in 10 miles at 200kts, my descent rate is 1667ft/min. That same crossing restriction at 400kts is 3333ft/min. Both of these are a 5 degree flight path angle, but there is a significant difference in the descent rate required.
06-19-2012, 08:14 AM
#29
Banned
Joined APC: Aug 2011
Posts: 1,134
Originally Posted by rustypigeon
It is a whole lot easier to use the 60:1 rule to calculate your flight path angle. Just get rid of the last 2 zeros in your altitude and you end up with 50/10= 5 degrees.
I never bother calculating my flight path angle. What is important to me is the descent rate required to meet the restriction. If i have to descend 5000ft in 10 miles at 200kts, my descent rate is 1667ft/min. That same crossing restriction at 400kts is 3333ft/min. Both of these are a 5 degree flight path angle, but there is a significant difference in the descent rate required.
I never bother calculating my flight path angle. What is important to me is the descent rate required to meet the restriction. If i have to descend 5000ft in 10 miles at 200kts, my descent rate is 1667ft/min. That same crossing restriction at 400kts is 3333ft/min. Both of these are a 5 degree flight path angle, but there is a significant difference in the descent rate required.
Nope, nuthin' wrong with getting down before hitting the fix, but in places like Mexico where youre non- radar combined with terrain or fuel critical it can kind of mtter.
06-19-2012, 12:41 PM
#30
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Joined APC: Apr 2010
Posts: 291
Originally Posted by Cubdriver
I was watching an aviation video where the pilot figured out his descent angle in order to make a fix and tell his autopilot what angle to use. Most people just use a descent rate in feet per minute. I never read of any easy way to do an angle calculation without a calculator, but this guy did it on his kneeboard real quick, and it was supposedly a real enactment, so I thought about it a little while, and came up with this fairly simple formula. Easy enough but still requires pen and paper.
Using the 10 degree pitch ladder on your ADI as 1.0 reference, select the pitch that represents the ratio of thousands of feet to loose over NM.
Example: you have to loose 15k' in 30NM, you would push halfway to 10 degrees, or 5 degrees.
Have to loose 5k' in 25nm, push to 2 degrees, etc.
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