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ETI TO THE ETP

  • jukzizy
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jukzizy created the topic: ETI TO THE ETP

Small piston day VFR charter operation:

Find the ETI to the ETP from alpha, Given the following

Distance from alpha to Bravo- 320 nm
Track 295*M
Tas 140 kts
W/V 250*M/30kts
fuel flow 120 L/hr
Taxi 20L
Etas- 138kts
320×159/280=181.7nm

Time= D/s
= 181÷117kts
= 93 minutes
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Carello replied the topic: ETI TO THE ETP

When doing this type of problem always start with a diagram.



In nil wind conditions, the ETP (CP) will be half-way between A and B. If a wind is blowing the ETP will be displaced upwind from the track mid-point position. Use this to check if you get a sensible answer after the calculations are done.

Track Home = 115 M
TAS = 140 kts
W/V = 250 M/30
GShome = 160 kts

DETP = (Total Dist x GShome)/(2xTAS) = (320 x 160)/(2 x 140) = 182.8 = 183 nm

Note: 183 nm is more than half-way to B - this is to be expected as we are punching into a headwind on route to B.

Track Out = 295 M
TAS = 140 kt
W/V = 250 M/30
GSout = 117 kts

TETP = DETP/GS out = 183/117 = 1.56 hr = 94 min
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bobtait replied the topic: ETI TO THE ETP

If that is one of my questions, could you please let me know where you found it.
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  • jukzizy
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jukzizy replied the topic: ETI TO THE ETP

it is a question from casa exam one of my friend got last time he sat his exam
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  • John.Heddles
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John.Heddles replied the topic: ETI TO THE ETP

A minor comment, if I may.

Some of the processes we use when working the wind triangle depend, for their validity, on the wind speed's being a sensibly small fraction of the TAS. As that fraction increases, things can require a little more care and precision and, in the extreme, the solution doesn't always function well at all.

For this particular case, the wind is 30 kt, a decent proportion of the TAS. The 2 x TAS approximation for (G/S on + G/S home) is starting to unravel a little.

Suggest you rework the calculations to check out the difference. Just for interest ....

Engineering specialist in aircraft performance and weight control.
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