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lucasgozzard created the topic: Answer discrepancy Simple 1 in 60 from the WAC

Hi Bob,

Just completed Question 1 from the Simple 1 in 60 exercises from the WAC on page 113.

My answers seem to be a little different from yours and am worried what tolerances they allow in the exam.

My answers to Scenario 1 are as follows:

FPT = 025 degrees M
TE = 12 degrees
TMG = 013 degrees M
CA = 5 degrees
TTI = 030 degrees M
HDG change req = 17 degrees R
HDG to fly after off track fix = 045 degrees M
GS = 133 kts
ETA at destination = 0304
Drift = 15 degrees L
HDG that would have kept the aircraft on track = 040 degrees M

bobtait replied the topic: Answer discrepancy Simple 1 in 60 from the WAC

There is nothing wrong with your reasoning. Sometimes, a measured distance may not be a whole number and that could give you a slightly different answer, especially when dealing with TE or CA. Remember that the one-in-sixty rule is not mathematically precise in any case. It's a 'rule of thumb'. It doesn't make much sense to argue about a fraction of a mile or a fraction of a degree. How perfectly can you hold a heading in practice?

John.Heddles replied the topic: Answer discrepancy Simple 1 in 60 from the WAC

Some follow up on Bob's comments.

The 1:60 "rule" is an approximation based on some basic relationships for angles measured in radians. For smallish angles (say, less than 12-15 degrees) it is quite accurate to use the angle measure as being equal to trigonometric ratios of interest. So, really, it should be the 1:57.3 (approximately, as pi comes into the reckoning) rule. Being interested in looking for simple ways of doing stuff, 57.3 is pretty close to 60, so we end up with the 1:60 rule.

A bit of sideline, useless information to tuck away, I guess.

Engineering specialist in aircraft performance and weight control.