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Old 10th February 2006 | 07:12
  #34 (permalink)  
BEagle
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Joined: May 1999
: ATP+Mil
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From: Quite near 'An aerodrome somewhere in England'
I came up with 104.5 knots using a web-based planning tool, and 105 using MDR:

Wind is 40 deg off, so about 3/4 to apply to the headwind, that's 15 knots, G/S is 105.

Which is 7/4 miles per minute and makes ETA estimates very simple.

The point which blagger and I have both made is that use of MDR for pre-flight planning is insufficiently accurate unless you also work out the planned G/S and corresponding fix point ETAs before flight. But it would be just as quick to use the whizz-wheel - particularly for time v distance estimates.

Using still-air IAS for low level high speed flying is one thing, ignoring W/V for pre-flight planning in a plastic puddlejumper at 3000 ft quite another. In the example I quoted, you would start your navigation exercise with an immediate 14% error which is wholly unacceptable. Try that on a PPL Skill Test and you will certainly fail.
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