PLT012 Commercial Question
Given: Aircraft weight is 3,700 pounds.
Airport Pressure Altitude is 4,000 feet.
Temperature at 4,000 feet is 21 degrees C.
Using a normal climb under the given conditions, how much fuel would be used from engine start to a pressure altitude of 12,000 feet.
Click here for discussion figure.
The fuel to climb to 4,000 from seal level is 12 pounds and the fuel used to climb to 12,000 feet from sea level is 37 pounds. The difference is 37 minus 12 equals 25 pounds.
In the notes section of the figure you will see that in #2 you need to increase time, fuel, and distance by 10 percent for each 7 degrees C above standard temperature. The standard temperature lapse rate is 2 degrees C per 1,000 feet. And the standard temperature at sea level is 15 degrees C.
Given this info we can get the standard temperature at 4,000 should be 7 degrees C (15 degrees C at sea level and the lapse rate is 2 degrees C per 1,000 feet or 15 degrees C – 8 degrees equals 7 degrees C).
So in the question “Given” section, our temperature of 21 degrees C is 14 degrees above standard. We have to increase the fuel by 10 percent for each 7 degrees above standard, you multiply standard conditions use by 120 percent for 14 degrees C over standard.
The fuel needed to climb is 30 pounds or 25 pounds times 1.20.
You also need to add 16 pounds of fuel for engine start, taxi, and takeoff. So 30 pounds plus 16 pounds equals 46 pounds.
