CALCULATING NAUTICAL MILE PER MINUTE

 

To quickly determine nautical miles per minute round your airspeed to the nearest 10.  Drop the zero and divide by 6.

Example:        TAS = 178 knots; round to 180 knots.

                        Drop the zero and divide by 6;

                        18 / 6 = 3 nm per minute

 

CALCULATING PRESSURE ALTITUDE

 

Pressure Altitude is needed to determine Density Altitude. To calculate Pressure Altitude you need the current barometric pressure and the field elevation.

                        Standard Barometric Pressure = 29.92

                        FE = Field Elevation

Example:        29.92

                     - 30.00

                     -     .08

                     x  1000

                     -       80

                     +      14 FE

                     -       66 PA

COMPUTING DENSITY ALTITUDE

 

Density altitude increases or decreases 120 feet for each 1 degree Celsius that the temperature varies from standard temperature.  (Standard temperature decreases 2 degrees C per 1000 feet increase in altitude.)

                                                DA      = PA + 120 (OAT - ISA)

                                                DA      = density altitude

                                                PA       = pressure altitude

                                                OAT    = outside air temperature

                                                ISA      = standard temperature

Example:        PA       = 6000 feet

                                                OAT    =     13 degrees C

                                                ISA      =       3 degrees C

                                                DA      = 6000 feet + 120 feet (13 - 3)

                                                DA      = 6000 feet + 1200 feet

                                                DA      = 7200 feet