Quick Formula you use ??

[cloudchaser5]

hi there

Just wondering if you would divulge your tips for quick calculations !!

For example you are 40,000 ft and told to descend to Fl 300 and be level in 40 Miles etc..

Really any formula you use when flying to check or recheck what the Fms computes .

Thanks in advance

[kwachon]

Try this for the descent and distance.

Distance To Descend 1. Take your altitude and multiply it by 3. That equals your distance in miles to begin your descent. 2. Now take half your ground speed. This is your rate of descent in hundreds of feet. Ex. If you are flying at 12000ft at a ground speed of 150kts and you need to descend to 2000ft, the difference is 10000ft. Multiply 10*3=30 miles out you must begin your descent. Half your ground speed is 75, add a zero, and 750 ft per minute is your rate of descent.

The distance to descend at 500 ft per minute. Equals 2 times the ground speed in miles-per-minute times the altitude to lose in thousands of feet. Ex. If ground speed in the descent is 155kts/180mph(3 miles-per-minute) and you must descend 8000ft, you must begin you descent 48 miles from the point at which you must be at the lower altitude. 2 times your 3 miles per minute ground speed equals 6 times 8 (your altitude to be lost in thousands) equals 48 miles.

[jr of dallas]

Basic maths:

10 000ft to lose in 40 miles, gives you 250 ft per NM wich is a 2,5 ° angle.
Now depending on your G/S but let's assume today we have 420 kts Ground Speed...that makes 7 nm per minute (420 kt/ 60 =7 nm/min)....you multiply your G/S per your angle (2,5°) 7 x 2,5 = 1750 ft/mn

You can do the same with the mach, if you descent for example at mach 0.7 :

7 x 2,5° = 1750 ft/mn

That's what I use when I 'm bored...

[usedtofly]

Even easier still........dial up a range ring.........set FLC and follow the banana!

Sorry guys, couldn't resist it!

[Bodie]

I have some basic calculations I use. Some might seem really basic, but here we go.

1. Calculate your true airspeed

I calculate this by taking the altitude in thousands of feet and multiplying it by 2. This is now a percentage value that the IAS will be increased by.

Examples:

180kts at 10,000ft => 10*2 = 20%. 20% of 180 = 36kts. 180 + 36 = 216kts TAS

300kts at 35,000ft => 35*2 = 70%. 70% of 300 = 210kts. 300 + 210 = 510kts TAS

2. Calculate groundspeed if it was unavailable.

I would note the distance travelled by the aircraft in 36 seconds, which is 1% of an hour. Then multiply this value by 100. For example, if the aircraft travelled 3.2nm then the groundspeed is 320kts.

3. Convert climb rate gradient to minimum climb rate

If you multiple the groundspeed by the climb gradient, you will find an approximate value representing climb rate.

For example, your groundspeed is 150kts and the climb gradient published on a SID is 5%. 5 x 150 = 750fpm.

4. Calculating crosswind.

Every one seems to know this, use the clock analogy. If the wind is 30 degrees off the runway, 30 on the clock would be 30 minutes, or half, so take half of the wind as crosswind.

5. Calculating headwind/tailwind.

The same as crosswind, but subtract the wind angle from ninety first. E.g. If the wind was 40 degrees of the runway at 24 knots. Take 90 and subtract 40 to give 50. With the clock analogy this is 50 minutes, or 5/6. Take 5/6 of 24 to give 20 knots head/tail wind.

6. To calculating drift

Always have in mind your max drift for the wind speed at your cruise level and the cruise TAS. Note the wind angle (which will change with time so keep looking at it). Use the same technique as 4 and 5 to calculate the total amount of drift but instead of using the wind speed, use your max drift. So if max drift was 10 degrees and the wind angle 30 degrees, take half of your max drift, or 5 degrees as your wind correction angle.

7. Calculating rate of descent on the glide

Everyone knows 5x groundspeed, or 10x div 2 which is easier.

Bodie

[Chippie Chappie]

As a ROUGH guide, I remember these figures (these figures work exactly for a G/S of 360 kts. Going faster? increase the ROD a bit).

1000'/min = 6 x Alt = distance
1500'/min = 4.5 x Alt = distance
2000'/min = 3 x Alt = distance
3000'/min = 2 x Alt = distance

So for the example of descending 10,000 (Alt = 10):

At 1,500'/min you would start the descent at 45NM
At 2000'/min, you would start the descent at 30NM.

You are between these two to split the distance, say 1700'/min. Now that you've started your descent, you can refine it using the FMS.

This is not as accurate as the other methods mentioned but I find it pretty good if I'm given an unexpected clearance to get me descending at an approximate rate.

If I have time to plan, I use kwachon's method.

Hope this helps,

Chips

[jr of dallas]

Falcon 50 with pro line 4 retrofit will do as well Honeywell Epic on 900 & 2000 Ez!

[Kilo-club SNA]

Well, if they say descend NOW, then you would have to figure out ROD based on speed etc. But if possible wouldn't you want to delay the descent until you are at a distance roughly 3x the altitude loss?

So in you example you need to be level in 40 milen and have 10000 feet to loose:
You need 30 miles to loose 10k, (3miles per 1000') so you can wait until you are within 30 miles of assaigned waypoint, or just start to ease it down and follow up with the math until you are once again in the "slot"