Pounds per minute method

T-39 FLIGHT PREPARATION

STUDENT GUIDE

DISTANCE TO

TIME TO

IAF

NEXT PT

IAF

NEXT PT

PT #1

140

770

0+20

1+50

PT #2

N/A

630

N/A

1+30

You mark on top of PT #1 at 40+00 with 6100# of fuel. Enroute to PT #2 you

complete a ground speed check: you are traveling 420 kts (7 NM/min). When you "freeze"

the fuel quantity and fuel flow, you have: time (44+00); fuel now (6040 #); fuel flow

(1800 #/hr); distance to PT #2 (112 NM). Compute IAF fuel for wings-level after PT #1

and IAF fuel after ground speed check.

Ground speed check:

112 NM 7 NM/min = 16 min to PT #2

16 min (to PT #2) + 90 min (PT #2 to IAF) = 106 min (to IAF)

(1)

Pounds per minute method:

Divide fuel flow by 60 to determine pounds per minute. Multiply pounds per minute

by minutes remaining to IAF.

1800#/hour 60 min/hour = 30.0 #/min

Wings Level:

106 min x 30.0#/min = 3180# fuel burned to IAF

6040# - 3180# = 2860# at IAF

(2)

Matrix method:

Set up a matrix of fuel used at convenient time intervals, then add available time

intervals to equal the time remaining. For example, at 1800 # per hour, the matrix would

be:

Time (min)

1800#

900#

450 #

300 #

180#

30#

To speed the matrix calculations, note that 30 minutes is half of 60 minutes, 15 minutes

is half of 30 minutes, and 6 minutes is a tenth of an hour.

Wings Level:

106 min

= 60 + 30 + 15 +1 = 1800 + 900 + 450 + 30 = 3180

= (60 x 2) - 15 + 1 = 3600 - 450 + 30 = 3180

then

6040# - 3180# = 2860# at IAF

(3)

Gauge method:

The gauge method is a variation on the matrix method. Instead of setting up a matrix,

we will use the fuel flow gauges. At fuel flow 1800#/hr, each gauge reads 900#/hr.

Time (min) minutes

Fuel (number of gauges)

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