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|Δημοσιεύθηκε: Πεμ 15 Απρ, 2010 10:47 pm Θέμα δημοσίευσης: Rules of Thumb
|Παρακάτω ακολουθούν ορισμένοι χρήσιμοι μνημονικοί κανόνες (Rules of Thumbs) που χρησιμοποιούνται κατά κόρον στις IFR διαδικασίες και όχι μόνο.
3 Degree Glide Slope
To maintain a 3 degree glideslope (eg: ILS) multiply the groundspeed you are achieving by 5. The resulting number is the rate of descent to fly.
Ex. Groundspeed = 110 Kts x 5 = 550fpm rate of descent to maintain 3 degree glideslope.
3 degree glide slope (Altitude)
With glideslope out on an ILS approach with DME, multiply the distance to go by 300. That should give you the height in feet you should be above the threshold.
4nms to the threshold. Multiply by 300 = 1200ft
3 times the altitude, plus ten
To estimate the point from the field to begin your descent, multiply your altitude (whole numbers)by three and add ten.
To descend from FL 350: 3 x 35 = 105 + 10 = 115 miles out.
EXACT rate of descent for a certain distance
Altitude in FL divided by Distance (NM) gives Flight Path Angle.
"Leaving FL310 descending FL230 to reach within 40 Miles"
80/40= 2 degrees pitch down
Top of Descend for a 3 degree glide slope
Multiply the Flight Level to loose by 3. Ground Speed / 2 X 10 = the required rate of descend for a 3 degree glide slope. E.g. FL350 -> FL100 = 25. Then 25x3=75NM. So we start descending at 75NM. Say GS=320Knots. 320/2 x 10 = 1600fpm is your desired rate of descend.
Distance to Descend
Take the difference in altitude and multiply times three. This will give you the distance from your crossing restriction to begin descent or "top of descent."
Now multiply your ground speed by six. This will give you your rate of descent in feet per minute.
You are level at FL210. ATC tells you to cross XYZ at 9000 feet. You are 85 NM from XYZ with a ground speed of 300 knots.
21000-9000 = 12000 (drop the zeroes and use 12) X 3 = 36nm
300 X 6 = 1800 or 1800 feet per minute
36 miles from XYZ you must start down at 1800 fpm or greater to meet the restriction.
When to begin your descent?
Divide the difference between Cruise Altitude and Descent Altitude by the Rate of Descent. That value is your Time to descend. Multiply this by your Groundspeed in Cruise and divide the result by 60. The result is the DME prior to which you need to begin your descent
EX: FL360 to 6000' = 30,000' /1500'per minute = 20 minutes.
Now, (20x420 Knots G/S)/60 = 140 nm from the desired point.
Rough estimate of True Airspeed
Take half of your altitude and add it to your indicated airspeed. E.g. 250KIAS @ FL240. 240/2 = 120 --> 250+120=370knots (TAS).