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140/50, and the TAS 260 kts (4
engines) and 210 kts (3 engines), find
the time and distance to the critical
point, assuming that engine failure
occurs there.
3. On an outbound track of 270°,
with 6 hours' fuel on board, a TAS
of 240 kts and a wind velocity of
290/45, give the time and distance
to the PNR from A. You must land
with 2 hours' fuel reserve.
4. If you plan to fly for an hour and
a half, and your machine uses 10
gals/hr, and you must land with 10
gals on board, what is your
minimum fuel before takeoff?
5. In 5 nm visibility, two aircraft
have a closing speed of 500 kts. How
much time is there for avoiding
action if seen at maximum range?
Some Answers
1. The groundspeed home is 180 kts
(240-60) and the groundspeed out is
300 (240+60), so the formula is:
480 x 180
30O + 180
180 nm at 300 kts is 36 minutes.
As a gross error check, work out the
times forward and back to see if they
are the same. It's 180 nm from the
CP to A, so at 180 kts, it will take an
hour to get there. From the CP to B,
356 Canadian Professional Pilot Studies
it's 300 nm which, at 300 kts, is also
1 hour.
2. The groundspeed home is 260 kts
(210 + 50) and out is 160 (210 – 50),
so the formula is:
345 x 260
260 + 160
The distance is 213.5 nm. At 210 kts
(all engines working) the time to get
there will be 61 minutes.
The worst place to get a reduction in
power is at the critical point itself,
where you are at the furthest point in
time from a suitable airfield, so the
calculations should be done with the
appropriate reduced speeds.
However, before the engine fails,
you are at full power, so using full
speed is appropriate for ETA.
3. Your actual endurance is 4 hours
(240 minutes), since you must land
with 2 hours' worth on board. The
groundspeed out is 196kts and back
is 283 kts, so the formula is:
240 x 282
196 + 282
which works out at 141.5 minutes.
At 196 kts, the distance is 462 nm.
The gross error check confirms that
the flight out and back should take
up the total endurance. 462 nm at
282 kts is 98.5 minutes, which,
added to 141.5 makes 4 hours (240
minutes).
4. 25 gals.
5. About 36 seconds.
Flight Operations
Fuelling
Jet and piston fuels mix differently
with contaminants (particularly
water), which is due to variations in
their specific gravities and
temperature. The specific gravity of
water, for example, is so close to
Avtur that it can take up to 4 hours
for it to settle out, whereas the same
process may take as little as half an
hour with Avgas. As a result, there is
always water suspended in jet fuel,
which must be kept within strict
limits, hence two filtration stages, for
solids and water. The latter doesn’t
burn, of course, and can freeze, but
it’s the fungi that gather round the
interface between it and the fuel that
is the real problem – it turns into a
dark-coloured slime which clings to
tank walls and supporting structures,
which not only alters the fuel
chemically, but will block filters as
well. Not much water is required for
this – trace elements are enough,
although, in reduced temperatures,
dissolved water will escape as free
water, and look like fog. Aviation
fuel is “clean” if a one-quart sample
is clear of sediment when viewed
through a clean, dry, clear glass
container, and looks clear and bright.
Note: It has been found that when
visible water is present in jet fuel
containing anti-icing additive, the
additive will separate from the fuel
and be attracted to the water. After a
certain amount, thought to be about
15%, the density of the new liquid
changes so much that it is not
identified as water, and will therefore
pass through water filters, and will
not be detected by water finding
paste. Where the ratio becomes 50%,
as much as 10% of whatever is going
through the filter could actually be
water, which is very likely to get to
the engine, since the filters on the
airframe itself are not as restrictive.
Turbine aircraft at high altitudes use
fuel heaters (actually heat exchangers
based on bleed air or engine oil) to
melt the ice crystals that form in the
fuel up there.
Aircraft parked overnight should
ideally have tanks completely filled
to stop condensation, but this is
358 Canadian Professional Pilot Studies
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