The correction at 10,000 feet MSL is zilch when you include
the altimeter of the reporting station, it isn't the
altitude above sea level, it is the amount of altitude
between the aircraft and the field elevation, which will be
only 2,000, the errors below that altitude are corrected and
cancelled when they take the altimeter setting.


"S Green" wrote in message
...
|
| "Peter" wrote in message
| ...
|
| "S Green" wrote
|
| Its in the JAR instrument test standards and features
within the learning
| objectives for the ATPL Met exam.
|
| Work it out. The difference is small on approach and
greater at high
| altitude but the examiner would be looking to see
whether you have taken
| account of the fact that temperature does make a
difference.
|
| In JAR land some say they are anal, others would take
the view that they
| do
| it properly.
|
| Is the pilot supposed to get the ATIS to get the surface
temp and work
| it out there and then?
|
| What is the typical correction, for an airport at say
1000ft AMSL
| which is ISA+10?
|
| +40 feet. Being the height in thousands * 4 * ISA
deviation
|
| In this case 1 * 4 * +10
|
| Temperatures - well you could get the temperature from
the ATIS but you
| also having sitting in front of you on the temperature
gauge too. I am sure
| the examiner will be looking at that and doing the mental
calculations.
|
| With a tolerance of +50 - 0 for at the decision height,
it does not take
| too much working out that you could blow the tolerances
when its either much
| warmer or much colder than ISA.
|
| Say you are planning to fly the check ride a bit too close
to the DH. On a
| cold day, you would be below the DH.
|
| On a very warm day, you could well above it and outside
the tolerance
| especially if you decided that you would aim to be about
say 40 ft above the
| DH. A 30 degree C day would have you actually higher than
indicated at say
| 252 ft and busted.
|
| When the temp is less than ISA the aircraft will be lower
than indicated
| height by 4ft /1000 for each degree c different.
|
| So at ISA dev -15 C at 200 ft above touch down, the actual
height will be
| 188.
| ISA -25 C at 200 ft above touch down, the actual height
will be 180.
|
| Its not hard to find places in Europe in winter where the
outside
| temperature is ISA -25 C after all, thats only -10 C.
|
| Hence why tables are produced to help pilots especially in
cold climates to
| make allowance.
|
| Here is a helpful presentation - I have flow into all
three of the field
| used as examples
http://williams.best.vwh.net/smxgigpdf/smxgig2000.pdf
|
| Another one from Transport Canada and I suggest you scroll
down to fig 9
| where there is a correction table laid out. The numbers
differ from mine
| because they round up so my 12 ft, they round up to 20 ft.
|
|