Use of Performance Charts

Question 1

Pressure Altitude

Answer 1

● Before using a performance chart, we almost always have to reduce the Altimeter Setting and either the Field Elevation or the Indicated Altitude to a Pressure Altitude.
➢ By reducing the prevailing conditions to a Pressure Altitude we are allowing our end result to have a common baseline altitude.
● Pressure Altitude is extremely important. It is used to determine Density Altitude, True Altitude, and True Airspeed.

crosswind chart example

atmospheric pressure formula

Question 2

Interpolating Results - Method 1

Answer 2

● If you have a temperature or an elevation that is between the numbers listed on a chart, you will need to interpolate!

Example: Temperature of 17°C at an elevation of 1 000 feet.
1. The ground roll at 10°C is 765 and 20°C is 825

2. Take the difference,
   825 – 765 = 60
3. 17 C is a little more than half the difference between 10 and 20, thus 17 is 70% more than 10°C.
   60 x 0.7 (70%) = 42
4. Add 42 to the takeoff distance at 10°C
   765 + 42 = 807

Question 3

Dry Grass Runway

Answer 3

Example: If your ground roll on pavement is 765 and the distance over 50 foot is 1 420. What is our takeoff distance on grass?
1. Add 15% of the ground roll figure.
765 x 0.15 (15%) = 115
2. Add 765 + 115 = 880
3. To calculate the distance over 50 feet, add 15% of the ground roll to the distance over 50 feet.
765 x .15 = 115
4. Distance over 50 feet is
1 420 + 115 = 1 535

Question 4

● What is your takeoff distance, ground roll and distance over 50 feet obstacle given:
➢ Winds 140° 10KT
➢ Temperature +30°C
➢ Altimeter 28.92 in Hg

Answer 4

Pressure Altitude
29.92
- 28.92
1.00
x 1 000
1 000
+ 3 937 Elevation
4 937 ft PA

At 4 000 ft 30C gnd = 1 190 and over 50 ft = 2 250 ft
At 5 000 ft 30C gnd = 1 315 and over 50 ft = 2525 ft

Differences gnd 125 and 50 ft 275
93.7% of each 117.13 and 257.68
Added to lower PA gives distance for PA 4 937 ft
Ground 1 307.13 ft
50 ft 2 507.68 ft

Using Runway 17 HW = 9 KT XW = 5 KT
Distance reduced by 10% for each 9 kts HW

Headwind reduces distance.
Gnd 1 307.13 – 130.71(10%) = 1 176.42 ft
50 ft 2 507.68 – 250.77(10%) = 2 256.91 ft

Grass adds 15% of the ground roll.
Gnd 1 176.42 + 176.46(15%) = 1 352.88 ft
50ft 2 256.91 + 176.46 = 2 433.37 ft

FINAL GROUND ROLL of 1 352.88 feet
FINAL OVER 50ft of 2 433.37 feet